Patent Publication Number: US-10316337-B2

Title: Genetically engineered bacterium for the production of isobutylene

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/658,668 filed Jul. 25, 2017, which is a continuation of U.S. patent application Ser. No. 15/293,191 filed Oct. 13, 2016 (now U.S. Pat. No. 9,738,875), which claims the benefit of U.S. Provisional Patent Application No. 62/240,850 filed Oct. 13, 2015, the entireties of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     With recent advances in fermentation and metabolic engineering, fermentation routes to various products have been identified and developed (Clomburg,  Appl Microbiol Biotechnol,  86: 419-434, 2010; Peralta-Yahya,  Biotechnol J,  5: 147-162, 2010; Cho,  Biotechnol Adv , pii: S0734-9750(14)00181-5, 2014. However, all of these fermentation routes are energy (ATP)-consuming or, at best, energy (ATP)-neutral, which restricts product yield in energy-limited systems and uncouples product production from microorganism growth. The present invention provides energy (ATP)-generating pathways that overcome these limitations by providing novel fermentation routes and pathways to a variety of products, including acids, alkenes, aldehydes, alcohols, and diols. These pathways are directly coupled to microorganism growth and offer high product yields. 
     In particular, the invention relates to fermentation pathways involving Ptb-Buk. Phosphate butyryltransferase (Ptb) (EC 2.3.1.19) natively catalyzes the reaction of butanoyl-CoA and phosphate to form CoA and butanoyl phosphate. Butyrate kinase (Buk) (EC 2.7.2.7) natively catalyzes the reaction of butanoyl phosphate and ADP to form butyrate (butanoate) and ATP. Accordingly, these enzymes together (Ptb-Buk) natively catalyze the conversion of butanoyl-CoA to butyrate and generate one ATP via substrate level phosphorylation (SLP). 
     The inventors have discovered that Ptb is promiscuous and is capable of accepting a variety of acyl-CoAs and enoyl-CoAs as substrates, such that Ptb-Buk may be used to convert a number of acyl-CoAs and enoyl-CoAs to their corresponding acids or alkenates, respectively, while simultaneously generating ATP via substrate level phosphorylation. 
     Furthermore, in combination with an aldehyde ferredoxin oxidoreductase (AOR) and an alcohol dehydrogenase, acids formed via the Ptb-Buk system can be further converted to their respective aldehydes, alcohols, or diols. AOR (EC 1.2.7.5) catalyzes the reaction of an acid and reduced ferredoxin (which can, for example, be generated from oxidation of CO or hydrogen) to form an aldehyde and oxidized ferredoxin. Alcohol dehydrogenase (EC 1.1.1.1 and EC 1.1.1.2) can convert an aldehyde and NAD(P)H to an alcohol and NAD(P). 
     Introduction of Ptb-Buk and/or AOR into a heterologous species, therefore, provides a novel, alternate route to the formation of native and non-native products, such as acids, alkenes, ketones, aldehydes, alcohols, and diols at high yields, thus overcoming limitations of the current state of the art. 
     SUMMARY OF THE INVENTION 
     The invention provides a genetically engineered bacterium comprising exogenous phosphate butyryltransferase (Ptb) and exogenous butyrate kinase (Buk) (Ptb-Buk). Generally, the Ptb-Buk acts on a non-native substrate, e.g., a substrate other than butanoyl-CoA and/or butanoyl phosphate, and produces a non-native product, e.g., a product other than butanoyl phosphate or butyrate. In certain embodiments, the Ptb-Buk converts acetoacetyl-CoA to acetoacetate, 3-hydroxyisovaleryl-CoA to 3-hydroxyisovalerate, 3-hydroxybutyryl-CoA to 3-hydroxybutyrate, or 2-hydroxyisobutyryl-CoA to 2-hydroxyisobutyrate. 
     The bacterium may produce one or more of an acid, an alkene, a ketone, an aldehyde, an alcohol, or a diol. More specifically, the bacterium may produce one or more of acetone or a precursor thereof, isopropanol or a precursor thereof, isobutylene or a precursor thereof, 3-hydroxybutyrate or a precursor thereof, 1,3-butanediol or a precursor thereof, 2-hydroxyisobutyrate or a precursor thereof, adipic acid or a precursor thereof, 1,3-hexanediol or a precursor thereof, 3-methyl-2-butanol or a precursor thereof, 2-buten-1-ol or a precursor thereof, isovalerate or a precursor thereof, or isoamyl alcohol or a precursor thereof. The bacterium does not typically produce butanol. 
     The bacterium may further comprise a disruptive mutation in a phosphotransacetylase (Pta) and an acetate kinase (Ack). The bacterium may further comprise a disruptive mutation in a thioesterase. In another embodiment, the invention provides a genetically engineered bacterium comprising exogenous Ptb-Buk and exogenous or endogenous aldehyde:ferredoxin oxidoreductase. 
     The invention further provides a method of producing a product comprising culturing the bacterium of any of the aforementioned embodiments in the presence of a substrate. The product may be, for example, acetone or a precursor thereof, isopropanol or a precursor thereof, isobutylene or a precursor thereof, 3-hydroxybutyrate or a precursor thereof, 1,3-butanediol or a precursor thereof, 2-hydroxyisobutyrate or a precursor thereof, adipic acid or a precursor thereof, 1,3-hexanediol or a precursor thereof, 3-methyl-2-butanol or a precursor thereof, 2-buten-1-ol or a precursor thereof, isovalerate or a precursor thereof, or isoamyl alcohol or a precursor thereof. Typically, the substrate is a gaseous substrate comprising, for example, one or more of CO, CO 2 , and H 2 . In one embodiment, the gaseous substrate is syngas. In another embodiment, the gaseous substrate is an industrial waste gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of metabolic pathways for the production of various products, including acetone, isopropanol, isobutylene, 3-hydroxybutyrate, 1,3-butanediol, and 2-hydroxyisobutyrate from acetyl-CoA. Acetyl-CoA may be generated from any suitable substrate, such as a carbohydrate (e.g., sugar) substrate or a gaseous substrate. In the present invention, acetyl-CoA is often generated from a gaseous substrate. Bold arrows indicate steps that may be catalyzed by Ptb-Buk. 
         FIG. 2  is a diagram showing the reactions natively catalyzed by Ptb-Buk, namely the conversion of butanoyl-CoA to butyrate and the generation of one ATP. 
         FIG. 3  is a diagram comparing the activities of CoA-transferase, thioesterase, and Ptb-Buk. 
         FIG. 4  is a graph showing average acetone production in  E. coli  BL21 (D3) modified with plasmids comprising exogenous genes. This data demonstrates the ability of Ptb-Buk to convert acetoacetyl-CoA to acetoacetate in  E. coli  in vivo. 
         FIG. 5  is a graph showing the effect of induction of  E. coli  BL21 (DE3) carrying both the pACYC-ptb-buk and pCOLA-thlA-adc plamids (expressing thiolase, Ptb-Buk, and acetoacate decarboxylase). 
         FIG. 6  is a diagram of a pathway designed to use Ptb-Buk for acetone production, while recycling the reducing equivalents produced in the production of (R)-3-hydroxybutyryl-CoA and the ATP generated by Ptb-Buk. 
         FIG. 7  is a diagram showing the role of aldehyde:ferredoxin oxidoreductase (AOR), ferredoxin, and Adh in the production of 1,3-butanediol in  C. autoethanogenum . More generally, AOR may be used to catalyze the conversion of an acid to an aldehyde and Adh may be used to catalyze the conversion of the aldehyde to an alcohol/diol. 
         FIG. 8  is a diagram showing the stereospecificity of Ptb-Buk for the production of (R)-3-hydroxybutyrate and 2-hydroxyisobutyrate. The term “native” in  FIG. 8  refers to native thioesterase. 
         FIG. 9  is a diagram showing the production of isobutene via Ptb-Buk conversion of 3-hydroxyisovaleryl-CoA and 3-hydroxyisovalerate using alternative pathway 1. 
         FIG. 10  is a diagram showing the production of isobutene via Ptb-Buk conversion of 3-hydroxyisovaleryl-CoA and 3-hydroxyisovalerate using alternative pathway 2. 
         FIG. 11  is a diagram showing the production of 1,3-butanediol via 3-butyraldehyde dehydrogenase (Bld). 
         FIG. 12  is a graph showing isopropanol production in  C. autoethanogenum  using the Ptb-Buk system over a control. ◯ pMTL85147-thlA-adc, ● pMTL85147-thlA-ptb-buk-adc. 
         FIGS. 13A-F  are graphs showing production of 3-hydroxybutyrate, acetate, ethanol, and acetone with modular plasmids in  E. coli  with different concentrations of inducer IPTG (0, 50, 100 μM).  FIG. 13A : pACYC-ptb-buk, pCOLA-thlA-adc, pCDF-phaB.  FIG. 13B : pACYC-ptb-buk, pCOLA-thlA-adc, pCDF-phaB-bdh1.  FIG. 13C : pCOLA-thlA-adc, pCDF-phaB-bdh1.  FIG. 13D : pCOLA-thlA-adc.  FIG. 13E : pCDF-phaB-bdh1.  FIG. 13F : pCDF-phaB. 
         FIG. 14  is a plasmid map of plasmid pMTL8225-budA::thlA-phaB. 
         FIG. 15  is a gel image of PCR verification of replacement of acetolactate synthase (budA) genes with thiolase (thlA) and 3-hydroxybutyryl-CoA dehydrogenase (phaB) genes in  C. autoethanogenum  for 4 clones (1, 4, 7, 9) compared to wild-type (W). All clones are positive as seen by a larger PCR fragment size compared to wild-type. 
         FIG. 16  is a graph showing fermentation profile of a batch fermentation  C. autoethanogenum  budA::thlAphaB strain and demonstrating 3-hydroxybutyrate and 1,3-butanediol formation from gas. 
         FIG. 17A  is a graph showing production of 1,3-BDO via thiolase, 3-hydroxybutyryl-CoA dehydrogenase (Bld), and butyraldehyde dehydrogenase.  FIG. 17B  is a graph showing the impact of bld expression on growth. 
         FIG. 18A  is a graph showing the formation of 3-hydroxybutyrate and 1,3-butanediol from gaseous substrate in  C. autoethanogenum  pMTL8315-Pfdx-hbd1-thlA.  FIG. 18B  is a graph showing the reduction of acetate to ethanol in the same culture. 
         FIG. 19  is a graph showing the fermentation profile for strain  C. autoethanogenum  pMTL8315-Pfdx-hbd1-thlA demonstrating formation of 3-hydroxybutyrate and 1,3-butanediol from gaseous substrate in continuous culture (where indicated, media was replenished continuously with given dilution rate D). 
         FIG. 20A  and  FIG. 20B  are graphs showing increased CoA hydrolysis activity on a range of acyl-CoAs (acetoacetyl-CoA, 3-hydroxybutyryl-CoA and 2-hydroxyisobutyryl-CoA) in  C. autoethanogenum  expressing the Ptb-Buk system from plasmid pMTL82256-ptb-buk compared to wild-type (WT). 
         FIG. 21A  and  FIG. 21B  are graphs showing reduced acyl-CoA hydrolysis activity of  C. autoethanogenum  strains with inactivated thioesterases (CT2640=thioesterase 1, CT 1524=thioesterase 2, CT1780=thioesterase 3) compared to activity found in  C. autoethanogenum  LZ1560 or LZ1561. 
         FIG. 22  is a graph showing increased specific isopropanol production in a  C. autoethanogenum  strain with disrupted thioesterase 3 CAETHG_1780 compared to wild-type  C. autoethanogenum.    
         FIGS. 23A-D  are graphs showing growth ( FIG. 23A ) and isopropanol ( FIG. 23B ), acetate ( FIG. 23C ), and ethanol ( FIG. 23D ) production profiles of  C. autoethanogenum  wild-type and strain with disrupted thioesterase 3 (CAETHG_1780) compared to wild-type  C. autoethanogenum.    
         FIG. 24  is a plasmid map of pMTL8225-pta-ack::ptb-buk. 
         FIG. 25  is a gel image indicating the replacement of pta and ack genes replaced with ptb and buk genes and ermB cassette. 
         FIG. 26  is a graph showing increased conversion 3-hydroxybutyrate to 1,3-BDO by overexpression of the aldehyde:ferredoxin oxidoreductase gene aor1. 
         FIG. 27  is a graph showing the activity of thioesterase TesB, Pta-Ack, and Ptb-Buk system on CoA hydrolysis of acetoacetyl-CoA, 3-hydroxybutyryl-CoA and 2-hydroxyisobutyryl-CoA compared to control (BL21 strain). Ptb-Buk shows highest activity, while Pta-Ack shows no activity. 
         FIGS. 28A and 28B  are graphs showing production of 3-hydroxybutyrate via Ptb-Buk in combination with an (S)-specific (Hbd) ( FIG. 28A ) or (R)-specific 3-hydroxybutyrate (PhaB) ( FIG. 28B ) dehydrogenase. 
         FIGS. 29A-D  are graphs showing LC-MS/MS detection of 2-hydroxyisobutyric acid (2-HIB) and 2-hydroxybutyrate (2-HB).  FIG. 29A : 1 mM 2-HIB standard.  FIG. 29B : 1 mM 2-HB standard. 
         FIG. 29C : 0.5 mM 2-HB and 2-HIB standard.  FIG. 29D : duplicate of  C. autoethanogenum  sample showing 2-HIB and 2-HB production from gas. 
         FIG. 30  is a set of graphs showing GC-MS confirmation of 2-hydroxyisobutyric acid (8.91 min) production. First panel:  C. autoethanogenum +pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-tesB. Second panel:  C. autoethanogenum +pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk (spectrum). Third panel:  E. coli +pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-tesB. Fourth panel:  E. coli +pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk. 
         FIG. 31  is a set of graphs of real time PCR showing expression of genes of the 2-HIBA pathway (thlA, hba, meaBhcmA, hcmB from pta-ack promoter and respectively Wood-Ljungdahl operon promoter) in  E. coli, C. autoethanogenum  LZ1561 at 30° C., and  C. autoethanogenum  LZ1561 at 37° C. 
         FIG. 32  is a diagram showing the production of various products in a microorganism comprising Ptb-Buk, AOR, and Adh. 
         FIG. 33  is a diagram showing the coupling firefly luciferase (Luc) to the Ptb-Buk system to characterize Ptb-Buk variants. 
         FIG. 34  is a diagram of metabolic pathways for the production of various products, including adipic acid. Bold arrows indicate steps that may be catalyzed by Ptb-Buk. 
         FIG. 35  is a diagram of metabolic pathways for the production of various products, including 1,3-hexanediol, 2-methyl-2-butanol, and 2-buten-1-ol. Bold arrows indicate steps that may be catalyzed by Ptb-Buk. 
         FIG. 36  is a diagram of metabolic pathways for the production of various products, including isovalerate and isoamyl alcohol. Bold arrows indicate steps that may be catalyzed by Ptb-Buk. 
         FIG. 37  is a graph of 3-HB production in  C. autoethanogenum  containing plasmid pMTL82256-thlA-ctfAB at various points of growth. 
         FIG. 38A  is a graph showing the growth and ethanol and 2,3-butanediol production profile of strain  C. autoethanogenum  pta-ack::ptb-buk+pMTL85147-thlA-ptb-buk-adc.  FIG. 38B  is a graph showing the isopropanol and 3-HB production profile of strain  C. autoethanogenum  pta-ack::ptb-buk+pMTL85147-thlA-ptb-buk-adc. 
         FIG. 39  is a diagram of a pathway scheme for producing a range of C 4 , C 6 , C 8 , C 10 , C 12 , C14 alcohols, ketones, enols or diols via combining known chain elongation pathway (Hbd, Crt, Bcd-EtfAB, Thl) with Ptb-Buk+AOR/Adc-Adh. 
         FIG. 40  is a graph showing production of 3-HB and 1,3-BDO by  C. autoethanogenum  transformed with plasmid pMTL83159-phaB-thlA at various points of growth. 
         FIG. 41  is a graph showing production of 3-HB and 1,3-BDO by  C. autoethanogenum  comprising budA knockout and pMTL-HBD-ThlA at various points of growth. 
         FIG. 42A  is a graph showing production of 3-HB in a  C. autoethanogenum  pMTL83159-phaB-thlA+pMTL82256 fermentation.  FIG. 42B  is a graph showing production of 3-HB in a  C. autoethanogenum  pMTL83159-phaB-thlA+pMTL82256-buk-ptb fermentation. 
         FIG. 43  is a graph showing the production of 3-HB in a  C. autoethanogenum  strain with thioesterase knockout (ACAETHG_1524) expressing plasmid pMTL83156-phaB-thlA with and without Ptb-Buk expression plasmid pMTL82256-buk-ptb. 
         FIG. 44  is a graph showing ethanol and 1,3-BDO production in a  C. autoethanogenum  strain expressing plasmid pMTL82256-hbd-thlA (2pf) with and without AOR overexpression plasmid pMTL83159-aor1 (+aor1). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Metabolic Pathways of  FIGS. 1 and 34-36   
       FIGS. 1 and 34-36  are diagrams of metabolic pathways for the production of various acid, alkene, ketone, aldehyde, alcohol, and diol products, including acetone, isopropanol, isobutylene, 3-hydroxybutyrate (R- and S-isomers), 1,3-butanediol, 2-hydroxyisobutyrate, adipic acid, 1,3-hexanediol, 2-methyl-2-butanol, 2-buten-1-ol, isovalerate, and isoamyl alcohol from a substrate. Bold arrows indicate steps that may be catalyzed by Ptb-Buk. Exemplary enzymes are provided for each of the steps and enzymatic pathways detailed in  FIGS. 1 and 34-36 . However, additional suitable enzymes may be known to a person of ordinary skill in the art. 
     Step 1 shows the conversion of acetyl-CoA to acetoacetyl-CoA. This step may be catalyzed by thiolase (i.e., acetyl-CoA acetyltransferase) (EC 2.3.1.9). The thiolase may be, for example, ThlA from  Clostridium acetobutylicum  (WP_010966157.1) (SEQ ID NO: 1), PhaA from  Cupriavidus  necator (WP_013956452.1) (SEQ ID NO: 2), BktB from  Cupriavidus necator  (WP_011615089.1) (SEQ ID NO: 3), or AtoB from  Escherichia coli  (NP_416728.1) (SEQ ID NO: 4).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  has native activity for this step. 
     Step 2 shows the conversion of acetoacetyl-CoA to acetoacetate. This step may be catalyzed by CoA-transferase (i.e., acetyl-CoA:acetoacetyl-CoA transferase) (EC 2.8.3.9). The CoA-transferase may be, for example, CtfAB, a heterodimer comprising subunits CtfA and CtfB, from  Clostridium beijerinckii  (CtfA, WP_012059996.1) (SEQ ID NO: 5) (CtfB, WP_012059997.1) (SEQ ID NO: 6). This step may also be catalyzed by thioesterase (EC 3.1.2.20). The thioesterase may be, for example, TesB from  Escherichia coli  (NP_414986.1) (SEQ ID NO: 7). This step may also be catalyzed by a putative thioesterase, e.g., from  Clostridium autoethanogenum  or  Clostridium ljungdahlii . In particular, three putative thioesterases have been identified in  Clostridium autoethanogenum : (1) “thioesterase 1” (AGY74947.1; annotated as palmitoyl-CoA hydrolase; SEQ ID NO: 8), (2) “thioesterase 2” (AGY75747.1; annotated as 4-hydroxybenzoyl-CoA thioesterase; SEQ ID NO: 9), and (3) “thioesterase 3” (AGY75999.1; annotated as putative thioesterase; SEQ ID NO: 10). Three putative thioesterases have also been identified in  Clostridium ljungdahlii : (1) “thioesterase 1” (ADK15695.1; annotated as predicted acyl-CoA thioesterase 1; SEQ ID NO: 11), (2) “thioesterase 2” (ADK16655.1; annotated as predicted thioesterase; SEQ ID NO: 12), and (3) “thioesterase 3” (ADK16959.1; annotated as predicted thioesterase; SEQ ID NO: 13). This step may also be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 3 shows the conversion of acetoacetate to acetone. This step may be catalyzed by an acetoacetate decarboxylase (EC 4.1.1.4). The acetoacetate decarboxylase may be, for example, Adc from  Clostridium beijerinckii  (WP_012059998.1) (SEQ ID NO: 14). This step may also be catalyzed by an alpha-ketoisovalerate decarboxylase (EC 4.1.1.74). The alpha-ketoisovalerate decarboxylase may be, for example, KivD from  Lactococcus lactis  (SEQ ID NO: 15).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step. Additionally,  Escherichia coli  does not have known native activity for this step. Rarely, conversion of acetoacetate to acetone may occur spontaneously. However, spontaneous conversion is highly inefficient and unlikely to result in the production of downstream products at desirable levels. 
     Step 4 shows the conversion of acetone to isopropanol. This step may be catalyzed by a primary:secondary alcohol dehydrogenase (EC 1.1.1.2). The primary:secondary alcohol dehydrogenase may be, for example, SecAdh from  Clostridium autoethanogenum  (AGY74782.1) (SEQ ID NO: 16), SecAdh from  Clostridium ljungdahlii  (ADK15544.1) (SEQ ID NO: 17), SecAdh from  Clostridium ragsdalei  (WP_013239134.1) (SEQ ID NO: 18), or SecAdh from  Clostridium beijerinckii  (WP_026889046.1) (SEQ ID NO: 19). This step may also be catalyzed by a primary:secondary alcohol dehydrogenase (EC 1.1.1.80), such as SecAdh from  Thermoanaerobacter brokii  (3FSR_A) (SEQ ID NO: 20).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step (Köpke,  Appl Environ Microbiol,  80: 3394-3403, 2014). However,  Escherichia coli  does not have known native activity for this step. Knocking down or knocking out this enzyme in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  results in the production and accumulation of acetone rather than isopropanol (WO 2015/085015). 
     Step 5 shows the conversion of acetone to 3-hydroxyisovalerate. This step may be catalyzed by a hydroxyisovalerate synthase, such as hydroxymethylglutaryl-CoA synthase (HMG-CoA synthase) (EC 2.3.3.10) from  Mus musculus  (SEQ ID NO: 21) (US 2012/0110001). The hydroxymethylglutaryl-CoA synthase may be engineered to improve activity.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 6 shows the conversion of 3-hydroxyisovalerate to isobutylene (isobutene). This step may be catalyzed by a hydroxyisovalerate phosphorylase/decarboxylase. This step may also be catalyzed by mevalonate diphosphate decarboxylase (hydroxyisovalerate decarboxylase) (EC 4.1.1.33). The mevalonate diphosphate decarboxylase may be, for example, Mdd from  Saccharomyces cerevisiae  (CAA96324.1) (SEQ ID NO: 22) or Mdd from  Picrophilus torridus  (WP_011178157.1) (SEQ ID NO: 23) (US 2011/0165644; van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step 
     Step 7 shows the conversion of acetone to 3-hydroxyisovaleryl-CoA. This step may be catalyzed by a 3-hydroxyisovaleryl-CoA synthase.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step 
     Step 8 shows the conversion of 3-hydroxyisovaleryl-CoA to 3-hydroxyisovalerate. This step may be catalyzed by CoA-transferase (i.e., acetyl-CoA:acetoacetyl-CoA transferase) (EC 2.8.3.9). The CoA-transferase may be, for example, CtfAB, a heterodimer comprising subunits CtfA and CtfB, from  Clostridium beijerinckii  (CtfA, WP_012059996.1) (SEQ ID NO: 5) (CtfB, WP_012059997.1) (SEQ ID NO: 6). This step may also be catalyzed by thioesterase (EC 3.1.2.20). The thioesterase may be, for example, TesB from  Escherichia coli  (NP_414986.1) (SEQ ID NO: 7). This step may also be catalyzed by a putative thioesterase, e.g., from  Clostridium autoethanogenum  or  Clostridium ljungdahlii . In particular, three putative thioesterases have been identified in  Clostridium autoethanogenum : (1) “thioesterase 1” (AGY74947.1; annotated as palmitoyl-CoA hydrolase; SEQ ID NO: 8), (2) “thioesterase 2” (AGY75747.1; annotated as 4-hydroxybenzoyl-CoA thioesterase; SEQ ID NO: 9), and (3) “thioesterase 3” (AGY75999.1; annotated as putative thioesterase; SEQ ID NO: 10). Three putative thioesterases have also been identified in  Clostridium ljungdahlii : (1) “thioesterase 1” (ADK15695.1; annotated as predicted acyl-CoA thioesterase 1; SEQ ID NO: 11), (2) “thioesterase 2” (ADK16655.1; annotated as predicted thioesterase; SEQ ID NO: 12), and (3) “thioesterase 3” (ADK16959.1; annotated as predicted thioesterase; SEQ ID NO: 13). This step may also be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 9 shows the conversion of acetyl-CoA to 3-methyl-2-oxopentanoate. This step encompasses a number of enzymatic reactions involved in the isoleucine biosynthesis pathway, which is natively present in many bacteria, including  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (and  Escherichia coli ). Enzymes involved in the conversion of acetyl-CoA to 3-methyl-2-oxopentanoate may include citramalate synthase (EC 2.3.1.182), 3-isopropylmalate dehydratase (EC 4.2.1.35), 3-isopropylmalate dehydrogenase (EC 1.1.1.85), acetolactate synthase (EC 2.2.1.6), ketol-acid reductoisomerase (EC 1.1.1.86), and/or dihydroxyacid dehydratase (EC 4.2.1.9). The citramalate synthase may be, for example, CimA from  Clostridium autoethanogenum  (AGY76958.1) (SEQ ID NO: 24) or CimA from  Methanocaldococcus jannaschii  (NP_248395.1) (SEQ ID NO: 25). The 3-isopropylmalate dehydratase may be, for example, LeuCD from  Clostridium autoethanogenum  (WP_023162955.1, LeuC; AGY77204.1, LeuD) (SEQ ID NOs: 26 and 27, respectively) or LeuCD from  Escherichia coli  (NP_414614.1, LeuC; NP_414613.1, LeuD) (SEQ ID NOs: 28 and 29, respectively). The 3-isopropylmalate dehydrogenase may be, for example, LeuB from  Clostridium autoethanogenum  (WP_023162957.1) (SEQ ID NO: 30) or LeuB from  Escherichia coli  (NP_414615.4) (SEQ ID NO: 31). The acetolactate synthase may be, for example, IlvBN from  Clostridium autoethanogenum  (AGY74359.1, IlvB; AGY74635.1, IlvB; AGY74360.1, IlvN) (SEQ ID NOs: 32, 33, and 34, respectively) or IlvBN from  Escherichia coli  (NP_418127.1, IlvB; NP_418126.1, IlvN) (SEQ ID NOs: 35 and 36, respectively). The ketol-acid reductoisomerase may be, for example, IlvC from  Clostridium autoethanogenum  (WP_013238693.1) (SEQ ID NO: 37) or IlvC from  Escherichia coli  (NP_418222.1) (SEQ ID NO: 38). The dihydroxyacid dehydratase may be, for example, IlvD from  Clostridium autoethanogenum  (WP_013238694.1) (SEQ ID NO: 39) or IlvD from  Escherichia coli  (YP_026248.1) (SEQ ID NO: 40).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. 
     Step 10 shows the conversion of 3-methyl-2-oxopentoate to 2-methylbutanoyl-CoA. This step may be catalyzed by ketoisovalerate oxidoreductase (EC 1.2.7.7). The ketoisovalerate oxidoreductase may be, for example, the VorABCD from  Methanothermobacter thermautotrophicus  (WP_010876344.1, VorA; WP_010876343.1, VorB; WP_010876342.1, VorC; WP_010876341.1, VorD) (SEQ ID NOs: 41-44, respectively) or VorABCD from  Pyococcus furiosus  (WP_011012106.1, VorA; WP_011012105.1, VorB; WP_011012108.1, VorC; WP_011012107.1, VorD) (SEQ ID NOs: 45-48, respectively). VorABCD is a 4-subunit enzyme.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 11 shows the conversion of 2-methylbutanoyl-CoA to 2-methylcrotonyl-CoA. This step may be catalyzed by 2-methylbutanoyl-CoA dehydrogenase (EC 1.3.99.12). The 2-methylbutanoyl-CoA dehydrogenase may be, for example, AcdH from  Streptomyces avermitilis  (AAD44196.1 or BAB69160.1) (SEQ ID NO: 49) or AcdH from  Streptomyces coelicolor  (AAD44195.1) (SEQ ID NO: 50).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 12 shows the conversion of 2-methylcrotonyl-CoA to 3-hydroxyisovaleryl-CoA. This step may be catalyzed by crotonase/3-hydroxybutyryl-CoA dehydratase (EC 4.2.1.55). The crotonase/3-hydroxybutyryl-CoA dehydratase may be, for example, Crt from  Clostridium beijerinckii  (ABR34202.1) (SEQ ID NO: 51), Crt from  Clostridium acetobutylicum  (NP_349318.1) (SEQ ID NO: 52), or LiuC from  Myxococcus xanthus  (WP_011553770.1). This step may also be catalyzed by crotonyl-CoA carboxylase-reductase (EC 1.3.1.86). The crotonyl-CoA carboxylase-reductase may be, for example, Ccr from  Treponema denticola  (NP_971211.1) (SEQ ID NO: 53). This step may also be catalyzed by crotonyl-CoA reductase (EC 1.3.1.44). The crotonyl-CoA reductase may be, for example, Ter from  Euglena gracilis  (AAW66853.1) (SEQ ID NO: 54). This step may also be catalyzed by a 3-hydroxypropionyl-CoA dehydratase (EC 4.2.1.116). This 3-hydroxypropionyl-CoA dehydratase may be, for example, Msed_2001 from  Metallosphaera sedula  (WP_012021928.1). This step may also be catalyzed by a enoyl-CoA hydratase. This enoyl-CoA hydratase (4.2.1.17) may be, for example, YngF from  Bacillus anthracis  (WP_000787371.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 13 shows the conversion of acetoacetyl-CoA to 3-hydroxybutyryl-CoA. This step may be catalyzed by 3-hydroxybutyryl-CoA dehydrogenase (EC 1.1.1.157). The 3-hydroxybutyryl-CoA dehydrogenase may be, for example, Hbd from  Clostridium beijerinckii  (WP_011967675.1) (SEQ ID NO: 55), Hbd from  Clostridium acetobutylicum  (NP_349314.1) (SEQ ID NO: 56), or Hbd1 from  Clostridium kluyveri  (WP_011989027.1) (SEQ ID NO: 57). This step may also be catalyzed by acetoacetyl-CoA reductase (EC 4.2.1.36). The acetoacetyl-CoA reductase may be, for example, PhaB from  Cupriavidus necator  (WP_010810131.1) (SEQ ID NO: 58). This step may also be catalyzed by acetoacetyl-CoA hydratase (EC 4.2.1.119). Of note, PhaB is R-specific and Hbd is S-specific. Additionally, Hbd1 from  Clostridium kluyveri  is NADPH-dependent and Hbd from  Clostridium acetobutylicum  and  Clostridium beijerinckii  are NADH-dependent.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 14 shows the conversion of 3-hydroxybutyryl-CoA to 3-hydroxybutyrate. This step may be catalyzed by thioesterase (EC 3.1.2.20). The thioesterase may be, for example, TesB from  Escherichia coli  (NP_414986.1) (SEQ ID NO: 7). This step may also be catalyzed by a putative thioesterase, e.g., from  Clostridium autoethanogenum  or  Clostridium ljungdahlii . In particular, three putative thioesterases have been identified in  Clostridium autoethanogenum : (1) “thioesterase 1” (AGY74947.1; annotated as palmitoyl-CoA hydrolase; SEQ ID NO: 8), (2) “thioesterase 2” (AGY75747.1; annotated as 4-hydroxybenzoyl-CoA thioesterase; SEQ ID NO: 9), and (3) “thioesterase 3” (AGY75999.1; annotated as putative thioesterase; SEQ ID NO: 10). Three putative thioesterases have also been identified in  Clostridium ljungdahlii : (1) “thioesterase 1” (ADK15695.1; annotated as predicted acyl-CoA thioesterase 1; SEQ ID NO: 11), (2) “thioesterase 2” (ADK16655.1; annotated as predicted thioesterase; SEQ ID NO: 12), and (3) “thioesterase 3” (ADK16959.1; annotated as predicted thioesterase; SEQ ID NO: 13). This step may also be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 15 shows the conversion of 3-hydroxybutyrate to acetoacetate. This step may be catalyzed by 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30). The 3-hydroxybutyrate dehydrogenase may be, for example, Bdh1 from  Ralstonia pickettii  (BAE72684.1) (SEQ ID NO: 60) or Bdh2 from  Ralstonia pickettii  (BAE72685.1) (SEQ ID NO: 61). The reverse reaction, the conversion of acetoacetate to 3-hydroxybutyrate, may be catalyzed by different 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) enzymes. For example, the conversion of acetoacetate to 3-hydroxybutyrate may be catalyzed by Bdh from  Clostridium autoethanogenum  (AGY75962) (SEQ ID NO: 62).  Clostridium ljungdahlii  and  Clostridium ragsdalei  likely have enzymes with similar activity.  Escherichia coli  does not have known native activity for this step. 
     Step 16 shows the conversion of 3-hydroxybutyrate to 3-hydroxybutyrylaldehyde. This step may be catalyzed by aldehyde:ferredoxin oxidoreductase (EC 1.2.7.5). The aldehyde:ferredoxin oxidoreductase (AOR) may be, for example, AOR from  Clostridium autoethanogenum  (WP_013238665.1; WP_013238675.1) (SEQ ID NOs: 63 and 64, respectively) or AOR from  Clostridium ljungdahlii  (ADK15073.1; ADK15083.1) (SEQ ID NOs: 65 and 66, respectively). In further embodiments, the aldehyde:ferredoxin oxidoreductase may be or may be derived, for example, from any of the following sources, the sequences of which are publically available: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Description 
                 Microrganism 
                 Accession 
                 GeneID 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 aldehyde:ferredoxin oxidoreductase 
                   Acidilobus saccharovorans  345-15 
                 NC_014374.1 
                 9498931 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Acidilobus saccharovorans  345-15 
                 NC_014374.1 
                 9499504 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Acidilobus saccharovorans  345-15 
                 NC_014374.1 
                 9499550 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Acidilobus saccharovorans  345-15 
                 NC_014374.1 
                 9498997 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum boonei  T469 
                 NC_013926.1 
                 8828075 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum boonei  T469 
                 NC_013926.1 
                 8828511 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum boonei  T469 
                 NC_013926.1 
                 8828305 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum boonei  T469 
                 NC_013926.1 
                 8827762 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum boonei  T469 
                 NC_013926.1 
                 8827370 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum  sp. MAR08-339 
                 NC_019942.1 
                 14306579 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum  sp. MAR08-339 
                 NC_019942.1 
                 14306982 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum  sp. MAR08-339 
                 NC_019942.1 
                 14306639 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aciduliprofundum  sp. MAR08-339 
                 NC_019942.1 
                 14307339 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Aeropyrum pernix  K1 
                 NC_000854.2 
                 1444491 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus fulgidus  DSM 4304 
                 NC_000917.1 
                 1483287 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus fulgidus  DSM 4304 
                 NC_000917.1 
                 1483233 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus fulgidus  DSM 4304 
                 NC_000917.1 
                 1483554 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus fulgidus  DSM 4304 
                 NC_000917.1 
                 1485513 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus profundus  DSM 
                 NC_013741.1 
                 8738726 
               
               
                   
                 5631 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus profundus  DSM 
                 NC_013741.1 
                 8740019 
               
               
                   
                 5631 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Archaeoglobus sulfaticallidus 
                 
                 NC_021169.1 
                 15392228 
               
               
                   
                 PM70-1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Archaeoglobus sulfaticallidus 
                 
                 NC_021169.1 
                 15393814 
               
               
                   
                 PM70-1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Archaeoglobus sulfaticallidus 
                 
                 NC_021169.1 
                 15391826 
               
               
                   
                 PM70-1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Archaeoglobus sulfaticallidus 
                 
                 NC_021169.1 
                 15393763 
               
               
                   
                 PM70-1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Archaeoglobus sulfaticallidus 
                 
                 NC_021169.1 
                 15393491 
               
               
                   
                 PM70-1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus veneficus  SNP6 
                 NC_015320.1 
                 10393142 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Archaeoglobus veneficus  SNP6 
                 NC_015320.1 
                 10395048 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldisphaera lagunensis  DSM 
                 NC_019791.1 
                 14212403 
               
               
                   
                 15908 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldisphaera lagunensis  DSM 
                 NC_019791.1 
                 14211524 
               
               
                   
                 15908 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldisphaera lagunensis  DSM 
                 NC_019791.1 
                 14212092 
               
               
                   
                 15908 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldisphaera lagunensis  DSM 
                 NC_019791.1 
                 14212561 
               
               
                   
                 15908 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5710116 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5710117 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5709088 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5708891 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5710478 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5710457 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Caldivirga maquilingensis  IC-167 
                 NC_009954.1 
                 5709696 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Caldiarchaeum 
                 
                 NC_022786.1 
                 17602865 
               
               
                   
                 subterraneum 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6094361 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6094198 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6093546 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6093319 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6094057 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Candidatus Korarchaeum 
                 
                 NC_010482.1 
                 6093563 
               
               
                   
                 cryptofilum OPF8 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Chloroflexus aurantiacus  J-10-fl 
                 NC_010175.1 
                 5828639 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Clostridium acetobutylicum  ATCC 
                 NC_003030.1 
                 1118201 
               
               
                   
                 824 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Clostridium botulinum  A sfr. ATCC 
                 NC_009495.1 
                 5187636 
               
               
                   
                 3502 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Clostridium botulinum  A str. Hall 
                 NC_009698.1 
                 5400593 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfovibrio vulgaris  str. 
                 NC_002937.3 
                 2796664 
               
               
                   
                 Hildenborough 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfovibrio vulgaris  str. 
                 NC_002937.3 
                 2795337 
               
               
                   
                 Hildenborough 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfurococcus fermentans  DSM 
                 NC_018001.1 
                 13061477 
               
               
                   
                 16532 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfurococcus fermentans  DSM 
                 NC_018001.1 
                 13061068 
               
               
                   
                 16532 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfurococcus fermentans  DSM 
                 NC_018001.1 
                 13062247 
               
               
                   
                 16532 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Desulfurococcus kamchatkensis 
                 
                 NC_011766.1 
                 7171099 
               
               
                   
                 1221n 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Desulfurococcus kamchatkensis 
                 
                 NC_011766.1 
                 7171759 
               
               
                   
                 1221n 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Desulfurococcus kamchatkensis 
                 
                 NC_011766.1 
                 7170725 
               
               
                   
                 1221n 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Desulfurococcus mucosus  DSM 
                 NC_014961.1 
                 10152801 
               
               
                   
                 2162 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8778536 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8779007 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8778940 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8779639 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8778820 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8778745 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ferroglobus placidus  DSM 10642 
                 NC_013849.1 
                 8779874 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Fervidicoccus fontis  Kam940 
                 NC_017461.1 
                 12449263 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Fervidicoccus fontis  Kam940 
                 NC_017461.1 
                 12449994 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Fervidicoccus fontis  Kam940 
                 NC_017461.1 
                 12449294 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Fervidicoccus fontis  Kam940 
                 NC_017461.1 
                 12449682 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Geobacter sulfurreducens  PCA 
                 NC_002939.5 
                 2685730 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Geobacter sulfurreducens  PCA 
                 NC_002939.5 
                 2687039 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halalkalicoccus jeotgali  B3 
                 NC_014297.1 
                 9418623 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halalkalicoccus jeotgali  B3 
                 NC_014297.1 
                 9418760 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halalkalicoccus jeotgali  B3 
                 NC_014297.1 
                 9420819 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halalkalicoccus jeotgali  B3 
                 NC_014297.1 
                 9418748 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  ATCC 33960 
                 NC_015948.1 
                 11051410 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  ATCC 33960 
                 NC_015948.1 
                 11050783 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  ATCC 33960 
                 NC_015948.1 
                 11051433 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  N601 
                 NC_023013.1 
                 23805333 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  N601 
                 NC_023013.1 
                 23805138 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula hispanica  N601 
                 NC_023013.1 
                 23804665 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula marismortui  ATCC 
                 NC_006396.1 
                 3127969 
               
               
                   
                 43049 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloarcula marismortui  ATCC 
                 NC_006396.1 
                 3129232 
               
               
                   
                 43049 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloferax mediterranei  ATCC 
                 NC_017941.2 
                 13028168 
               
               
                   
                 33500 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloferax mediterranei  ATCC 
                 NC_017941.2 
                 13028399 
               
               
                   
                 33500 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloferax volcanii  DS2 
                 NC_013964.1 
                 8919329 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloferax volcanii  DS2 
                 NC_013964.1 
                 8919033 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloferax volcanii  DS2 
                 NC_013967.1 
                 8926544 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halogeometricum borinquense  DSM 
                 NC_014735.1 
                 9989054 
               
               
                   
                 11551 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halogeometricum borinquense  DSM 
                 NC_014729.1 
                 9994424 
               
               
                   
                 11551 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halogeometricum borinquense  DSM 
                 NC_014729.1 
                 9992444 
               
               
                   
                 11551 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11095016 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11095541 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11094595 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11096497 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11094563 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   halophilic archaeon  DL31 
                 NC_015954.1 
                 11095602 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halopiger xanaduensis  SH-6 
                 NC_015666.1 
                 10799161 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halopiger xanaduensis  SH-6 
                 NC_015658.1 
                 10795465 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halopiger xanaduensis  SH-6 
                 NC_015666.1 
                 10798686 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halopiger xanaduensis  SH-6 
                 NC_015666.1 
                 10796679 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halorubrum lacusprofundi  ATCC 
                 NC_012029.1 
                 7400122 
               
               
                   
                 49239 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halorubrum lacusprofundi  ATCC 
                 NC_012029.1 
                 7400291 
               
               
                   
                 49239 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Halorubrum lacusprofundi  ATCC 
                 NC_012029.1 
                 7400689 
               
               
                   
                 49239 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013744.1 
                 8744461 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013744.1 
                 8744695 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013743.1 
                 8740954 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013745.1 
                 8745418 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013743.1 
                 8742968 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013743.1 
                 8741246 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013743.1 
                 8741269 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Haloterrigena turkmenica  DSM 
                 NC_013745.1 
                 8745313 
               
               
                   
                 5511 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Hyperthermus butylicus  DSM 5456 
                 NC_008818.1 
                 4781896 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Hyperthermus butylicus  DSM 5456 
                 NC_008818.1 
                 4782266 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Hyperthermus butylicus  DSM 5456 
                 NC_008818.1 
                 4782804 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Hyperthermus butylicus  DSM 5456 
                 NC_008818.1 
                 4781774 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ignicoccus hospitalis  KIN4/I 
                 NC_009776.1 
                 5562477 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ignicoccus hospitalis  KIN4/I 
                 NC_009776.1 
                 5562774 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Ignisphaera aggregans  DSM 17230 
                 NC_014471.1 
                 9716798 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Methanocaldococcus jannaschii 
                 
                 NC_000909.1 
                 1452083 
               
               
                   
                 DSM 2661 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella arvoryzae  MRE50 
                 NC_009464.1 
                 5142690 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella arvoryzae  MRE50 
                 NC_009464.1 
                 5143773 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella conradii  HZ254 
                 NC_017034.1 
                 11972399 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella conradii  HZ254 
                 NC_017034.1 
                 11971349 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella paludicola  SANAE 
                 NC_013665.1 
                 8680711 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocella paludicola  SANAE 
                 NC_013665.1 
                 8680676 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanocorpusculum labreanum  Z 
                 NC_008942.1 
                 4795790 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanoculleus marisnigri  JR1 
                 NC_009051.1 
                 4847673 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanohalobium evestigatum  Z- 
                 NC_014253.1 
                 9347460 
               
               
                   
                 7303 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanohalobium evestigatum  Z- 
                 NC_014253.1 
                 9347022 
               
               
                   
                 7303 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanolobus psychrophilus  R15 
                 NC_018876.1 
                 13845119 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Methanomethylovorans hollandica 
                 
                 NC_019977.1 
                 14408029 
               
               
                   
                 DSM 15978 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosaeta harundinacea  6Ac 
                 NC_017527.1 
                 12511443 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosaeta thermophila  PT 
                 NC_008553.1 
                 4462364 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosalsum zhilinae  DSM 4017 
                 NC_015676.1 
                 10822365 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina acetivorans  C2A 
                 NC_003552.1 
                 1475882 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina acetivorans  C2A 
                 NC_003552.1 
                 1474856 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina acetivorans  C2A 
                 NC_003552.1 
                 1473602 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina barkeri  str. Fusaro 
                 NC_007355.1 
                 3625763 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Go1 
                 NC_003901.1 
                 1479263 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Go1 
                 NC_003901.1 
                 1481668 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Go1 
                 NC_003901.1 
                 1480987 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Tuc01 
                 NC_020389.1 
                 14656065 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Tuc01 
                 NC_020389.1 
                 14656771 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosarcina mazei  Tuc01 
                 NC_020389.1 
                 14654304 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanosphaerula palustris  E1-9c 
                 NC_011832.1 
                 7271108 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methanospirillum hungatei  JF-1 
                 NC_007796.1 
                 3924565 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Methylomicrobium alcaliphilum  20Z 
                 NC_016112.1 
                 11361147 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Moorella thermoacetica  ATCC 
                 NC_007644.1 
                 3831332 
               
               
                   
                 39073 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Moorella thermoacetica  ATCC 
                 NC_007644.1 
                 3830998 
               
               
                   
                 39073 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Moorella thermoacetica  ATCC 
                 NC_007644.1 
                 3831866 
               
               
                   
                 39073 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrialba magadii  ATCC 43099 
                 NC_013922.1 
                 8824961 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrialba magadii  ATCC 43099 
                 NC_013922.1 
                 8823392 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrialba magadii  ATCC 43099 
                 NC_013923.1 
                 8826737 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrialba magadii  ATCC 43099 
                 NC_013922.1 
                 8825516 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrinema pellirubrum  DSM 15624 
                 NC_019962.1 
                 14335278 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrinema pellirubrum  DSM 15624 
                 NC_019962.1 
                 14333050 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrinema pellirubrum  DSM 15624 
                 NC_019962.1 
                 14333754 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natrinema  sp. J7-2 
                 NC_018224.1 
                 13349954 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14210296 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14207133 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14209682 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14207576 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14206941 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronobacterium gregoryi  SP2 
                 NC_019792.1 
                 14206532 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronococcus occultus  SP4 
                 NC_019974.1 
                 14403316 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronococcus occultus  SP4 
                 NC_019974.1 
                 14405255 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronococcus occultus  SP4 
                 NC_019974.1 
                 14403781 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronococcus occultus  SP4 
                 NC_019974.1 
                 14402014 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas moolapensis  8.8.11 
                 NC_020388.1 
                 14651997 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas moolapensis  8.8.11 
                 NC_020388.1 
                 14652892 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas moolapensis  8.8.11 
                 NC_020388.1 
                 14651999 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas pharaonis  DSM 2160 
                 NC_007427.1 
                 3694680 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas pharaonis  DSM 2160 
                 NC_007426.1 
                 3702508 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas pharaonis  DSM 2160 
                 NC_007426.1 
                 3702507 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Natronomonas pharaonis  DSM 2160 
                 NC_007426.1 
                 3702509 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum aerophilum  str. IM2 
                 NC_003364.1 
                 1464236 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum aerophilum  str. IM2 
                 NC_003364.1 
                 1464102 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum aerophilum  str. IM2 
                 NC_003364.1 
                 1465126 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum aerophilum  str. IM2 
                 NC_003364.1 
                 1465445 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum arsenaticum  DSM 
                 NC_009376.1 
                 5055904 
               
               
                   
                 13514 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum arsenaticum  DSM 
                 NC_009376.1 
                 5055700 
               
               
                   
                 13514 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum arsenaticum  DSM 
                 NC_009376.1 
                 5054881 
               
               
                   
                 13514 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum arsenaticum  DSM 
                 NC_009376.1 
                 5054644 
               
               
                   
                 13514 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum arsenaticum  DSM 
                 NC_009376.1 
                 5054547 
               
               
                   
                 13514 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum calidifontis  JCM 
                 NC_009073.1 
                 4910224 
               
               
                   
                 11548 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum calidifontis  JCM 
                 NC_009073.1 
                 4908822 
               
               
                   
                 11548 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum calidifontis  JCM 
                 NC_009073.1 
                 4909927 
               
               
                   
                 11548 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum calidifontis  JCM 
                 NC_009073.1 
                 4910099 
               
               
                   
                 11548 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum islandicum  DSM 4184 
                 NC_008701.1 
                 4617364 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum islandicum  DSM 4184 
                 NC_008701.1 
                 4616724 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum islandicum  DSM 4184 
                 NC_008701.1 
                 4617494 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum neutrophilum  V24Sta 
                 NC_010525.1 
                 6165427 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum neutrophilum  V24Sta 
                 NC_010525.1 
                 6164958 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum neutrophilum  V24Sta 
                 NC_010525.1 
                 6164976 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum oguniense  TE7 
                 NC_016885.1 
                 11853778 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum oguniense  TE7 
                 NC_016885.1 
                 11854024 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum oguniense  TE7 
                 NC_016885.1 
                 11856490 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum oguniense  TE7 
                 NC_016885.1 
                 11856176 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum oguniense  TE7 
                 NC_016885.1 
                 11854908 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum  sp. 1860 
                 NC_016645.1 
                 11594868 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum  sp. 1860 
                 NC_016645.1 
                 11596631 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrobaculum  sp. 1860 
                 NC_016645.1 
                 11594049 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus abyssi  GE5 
                 NC_000868.1 
                 1496313 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus abyssi  GE5 
                 NC_000868.1 
                 1495669 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus abyssi  GE5 
                 NC_000868.1 
                 1496580 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus abyssi  GE5 
                 NC_000868.1 
                 1495287 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  COM1 
                 NC_018092.1 
                 13302148 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  COM1 
                 NC_018092.1 
                 13301806 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  COM1 
                 NC_018092.1 
                 13301219 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  COM1 
                 NC_018092.1 
                 13300785 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  DSM 3638 
                 NC_003413.1 
                 1468181 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  DSM 3638 
                 NC_003413.1 
                 1469073 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus furiosus  DSM 3638 
                 NC_003413.1 
                 1469843 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus horikoshii  OT3 
                 NC_000961.1 
                 1443218 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus horikoshii  OT3 
                 NC_000961.1 
                 1443341 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus horikoshii  OT3 
                 NC_000961.1 
                 1443932 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus horikoshii  OT3 
                 NC_000961.1 
                 1443598 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. NA2 
                 NC_015474.1 
                 10555029 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. NA2 
                 NC_015474.1 
                 10554020 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. NA2 
                 NC_015474.1 
                 10555341 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. ST04 
                 NC_017946.1 
                 13022107 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. ST04 
                 NC_017946.1 
                 13022436 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus  sp. ST04 
                 NC_017946.1 
                 13021314 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus yayanosii  CH1 
                 NC_015680.1 
                 10837518 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus yayanosii  CH1 
                 NC_015680.1 
                 10837112 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrococcus yayanosii  CH1 
                 NC_015680.1 
                 10837264 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrolobus fumarii  1A 
                 NC_015931.1 
                 11138144 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrolobus fumarii  1A 
                 NC_015931.1 
                 11138776 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Pyrolobus fumarii  1A 
                 NC_015931.1 
                 11139127 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Rhodospirillum rubrum  ATCC 
                 NC_007643.1 
                 3833668 
               
               
                   
                 11170 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus hellenicus  DSM 
                 NC_014205.1 
                 9234557 
               
               
                   
                 12710 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus hellenicus  DSM 
                 NC_014205.1 
                 9233414 
               
               
                   
                 12710 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus hellenicus  DSM 
                 NC_014205.1 
                 9234134 
               
               
                   
                 12710 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus hellenicus  DSM 
                 NC_014205.1 
                 9234110 
               
               
                   
                 12710 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus marinus  F1 
                 NC_009033.1 
                 4907444 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Staphylothermus marinus  F1 
                 NC_009033.1 
                 4907343 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermanaerovibrio 
                 
                 NC_013522.1 
                 8630284 
               
               
                   
                   acidaminovorans  DSM 6589 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermanaerovibrio 
                 
                 NC_013522.1 
                 8630027 
               
               
                   
                   acidaminovorans  DSM 6589 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermanaerovibrio 
                 
                 NC_013522.1 
                 8630623 
               
               
                   
                   acidaminovorans  DSM 6589 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermoanaerobacter wiegelii 
                 
                 NC_015958.1 
                 11082596 
               
               
                   
                 Rt8.B1 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus barophilus  MP 
                 NC_014804.1 
                 10041639 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus barophilus  MP 
                 NC_014804.1 
                 10041106 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus barophilus  MP 
                 NC_014804.1 
                 10042460 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermococcus cleftensis 
                 
                 NC_018015.1 
                 13037745 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermococcus cleftensis 
                 
                 NC_018015.1 
                 13038896 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermococcus cleftensis 
                 
                 NC_018015.1 
                 13037242 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus gammatolerans  EJ3 
                 NC_012804.1 
                 7988317 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus gammatolerans  EJ3 
                 NC_012804.1 
                 7987451 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus kodakarensis  KOD1 
                 NC_006624.1 
                 3233851 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus kodakarensis  KOD1 
                 NC_006624.1 
                 3233735 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus litoralis  DSM 5473 
                 NC_022084.1 
                 16550741 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus litoralis  DSM 5473 
                 NC_022084.1 
                 16548761 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus litoralis  DSM 5473 
                 NC_022084.1 
                 16550885 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus onnurineus  NA1 
                 NC_011529.1 
                 7018383 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus onnurineus  NA1 
                 NC_011529.1 
                 7016739 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus onnurineus  NA1 
                 NC_011529.1 
                 7017051 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus onnurineus  NA1 
                 NC_011529.1 
                 7017476 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8096638 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8096005 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8096629 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8095463 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8096131 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus sibiricus  MM 739 
                 NC_012883.1 
                 8096636 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. 4557 
                 NC_015865.1 
                 11015504 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. 4557 
                 NC_015865.1 
                 11015249 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. 4557 
                 NC_015865.1 
                 11015571 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. AM4 
                 NC_016051.1 
                 7419050 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. AM4 
                 NC_016051.1 
                 7418514 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermococcus  sp. AM4 
                 NC_016051.1 
                 7420292 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermodesulfovibrio yellowstonii 
                 
                 NC_011296.1 
                 6941429 
               
               
                   
                 DSM 11347 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermodesulfovibrio yellowstonii 
                 
                 NC_011296.1 
                 6943174 
               
               
                   
                 DSM 11347 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                 
                   Thermodesulfovibrio yellowstonii 
                 
                 NC_011296.1 
                 6941905 
               
               
                   
                 DSM 11347 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum pendens  Hrk 5 
                 NC_008698.1 
                 4602054 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum pendens  Hrk 5 
                 NC_008698.1 
                 4601386 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum pendens  Hrk 5 
                 NC_008698.1 
                 4600878 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum pendens  Hrk 5 
                 NC_008698.1 
                 4600730 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum  sp. 1910b 
                 NC_022093.1 
                 16572780 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum  sp. 1910b 
                 NC_022093.1 
                 16572926 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum  sp. 1910b 
                 NC_022093.1 
                 16573009 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermofilum  sp. 1910b 
                 NC_022093.1 
                 16574342 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermogladius cellulolyticus  1633 
                 NC_017954.1 
                 13012904 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoplasma acidophilum  DSM 
                 NC_002578.1 
                 1456355 
               
               
                   
                 1728 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoplasma acidophilum  DSM 
                 NC_002578.1 
                 1456646 
               
               
                   
                 1728 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoplasma volcanium  GSS1 
                 NC_002689.2 
                 1441901 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoplasma volcanium  GSS1 
                 NC_002689.2 
                 1441379 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus tenax  Kra 1 
                 NC_016070.1 
                 11262174 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus tenax  Kra 1 
                 NC_016070.1 
                 11262275 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus tenax  Kra 1 
                 NC_016070.1 
                 11262652 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus tenax  Kra 1 
                 NC_016070.1 
                 11262926 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus uzoniensis  768-20 
                 NC_015315.1 
                 10361668 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus uzoniensis  768-20 
                 NC_015315.1 
                 10361250 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermoproteus uzoniensis  768-20 
                 NC_015315.1 
                 10360972 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermosphaera aggregans  DSM 
                 NC_014160.1 
                 9165115 
               
               
                   
                 11486 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermosphaera aggregans  DSM 
                 NC_014160.1 
                 9165462 
               
               
                   
                 11486 
                   
                   
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermus thermophilus  HB8 
                 NC_006461.1 
                 3168554 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Thermus thermophilus  HB8 
                 NC_006461.1 
                 3168612 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta distributa  DSM 14429 
                 NC_014537.1 
                 9753145 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta distributa  DSM 14429 
                 NC_014537.1 
                 9750947 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta distributa  DSM 14429 
                 NC_014537.1 
                 9750989 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta distributa  DSM 14429 
                 NC_014537.1 
                 9753486 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta distributa  DSM 14429 
                 NC_014537.1 
                 9751414 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288238 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288894 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288574 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288827 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288607 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288523 
               
               
                 aldehyde:ferredoxin oxidoreductase 
                   Vulcanisaeta moutnovskia  768-28 
                 NC_015151.1 
                 10288815 
               
               
                   
               
            
           
         
       
     
     AOR catalyzes the reaction of an acid and reduced ferredoxin to form an aldehyde and oxidized ferredoxin. In acetogens, this reaction can be coupled to oxidation CO (via CO dehydrogenase, EC 1.2.7.4) or hydrogen (via ferredoxin-dependent hydrogenase, EC 1.12.7.2 or 1.12.1.4) that both yield reduced ferredoxin (Köpke,  Curr Opin Biotechnol  22: 320-325, 2011; Köpke,  PNAS  USA, 107: 13087-13092, 2010).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous AOR or introduction of an exogenous AOR in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields. Alternatively, exogenous AOR may be introduced into a microorganism that does not natively comprise AOR, e.g.,  E. coli . In particular, the co-expression of Ptb-Buk and AOR (and, optionally, Adh) may enable such a microorganism to produce new non-native products. 
     Step 17 shows the conversion of 3-hydroxybutyrylaldehyde to 1,3-butanediol. This step may be catalyzed by alcohol dehydrogenase (EC 1.1.1.1. or 1.1.1.2.). Alcohol dehydrogenase can convert an aldehyde and NAD(P)H to an alcohol and NAD(P). The alcohol dehydrogenase may be, for example, Adh from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 67),  Clostridium ljungdahlii  (ADK17019.1) (SEQ ID NO: 68), or  Clostridium ragsdalei , BdhB from  Clostridium acetobutylicum  (NP_349891.1) (SEQ ID NO: 69), Bdh from  Clostridium beijerinckii  (WP_041897187.1) (SEQ ID NO: 70), Bdh1 from  Clostridium ljungdahlii  (YP_003780648.1) (SEQ ID NO: 71), Bdh1 from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 72), Bdh2 from  Clostridium ljungdahlii  (YP_003782121.1) (SEQ ID NO: 73), Bdh2 from  Clostridium autoethanogenum  (AGY74784.1) (SEQ ID NO: 74), AdhE1 from  Clostridium acetobutylicum  (NP_149325.1) (SEQ ID NO: 75), AdhE2 from  Clostridium acetobutylicum  (NP_149199.1) (SEQ ID NO: 76), AdhE from  Clostridium beijerinckii  (WP_041893626.1) (SEQ ID NO: 77), AdhE1 from  Clostridium autoethanogenum  (WP_023163372.1) (SEQ ID NO: 78), or AdhE2 from  Clostridium autoethanogenum  (WP_023163373.1) (SEQ ID NO: 79).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous alcohol dehydrogenase or introduction of an exogenous alcohol dehydrogenase in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields.  Escherichia coli  likely does not have native activity for this step. 
     Step 18 shows the conversion of 3-hydroxybutyryl-CoA to 3-hydroxybutyrylaldehyde. This step may be catalyzed by butyraldehyde dehydrogenase (EC 1.2.1.57). The butyraldehyde dehydrogenase may be, for example, Bld from  Clostridium saccharoperbutylacetonicum  (AAP42563.1) (SEQ ID NO: 80).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 19 shows the conversion of 3-hydroxybutyryl-CoA to 2-hydroxyisobutyryl-CoA. This step may be catalyzed by 2-hydroxyisobutyryl-CoA mutase (EC 5.4.99.-). The 2-hydroxyisobutyryl-CoA mutase may be, for example, HcmAB from  Aquincola tertiaricarbonis  (AFK77668.1, large subunit; AFK77665.1, small subunit) (SEQ ID NOs: 81 and 82, respectively) or HcmAB from  Kyrpidia tusciae  (WP_013074530.1, large subunit; WP_013074531.1, small subunit) (SEQ ID NOs: 83 and 84, respectively). Chaperone MeaB (AFK77667.1 , Aquincola tertiaricarbonis ; WP_013074529.1 , Kyrpidia tusciae ) (SEQ ID NOs: 85 and 86, respectively) has been described to improve activity of HcmAB by reactivating HcmAB, although MeaB is not required for HcmAB function (Yaneva,  J Biol Chem,  287: 15502-15511, 2012).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 20 shows the conversion of 2-hydroxyisobutyryl-CoA to 2-hydroxyisobutyrate. This step may be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 21 shows the conversion of acetyl-CoA to succinyl-CoA. This step encompasses a number of enzymatic reactions involved in the reductive TCA pathway, which is natively present in many bacteria, including  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (and  Escherichia coli ) (Brown,  Biotechnol Biofuels,  7: 40, 2014; U.S. Pat. No. 9,297,026). Enzymes involved in the conversion of acetyl-CoA to succinyl-CoA may include pyruvate:ferredoxin oxidoreductase (PFOR) (EC 1.2.7.1), pyruvate carboxylase (PYC) (EC 6.4.1.1), malic enzyme/malate dehydrogenase (EC 1.1.1.38, EC 1.1.1.40), pyruvate phosphate dikinase (PPDK) (EC:2.7.9.1), PEP carboxykinase (PCK) (EC 4.1.1.49), fumarate hydratase/fumerase (EC 4.2.1.2), fumarate reductase (EC 1.3.5.1)/succinate dehydrogenase (EC 1.3.5.4), and succinyl-CoA synthetase (EC 6.2.1.5). The pyruvate:ferredoxin oxidoreductase may be, for example, from  Clostridium autoethanogenum  (AGY75153, AGY77232) or  Escherichia coli  (NP_415896). The pyruvate carboxylase may be, for example, from  Clostridium autoethanogenum  (AGY75817). The malic enzyme/malate dehydrogenase may be, for example, from  Clostridium autoethanogenum  (AGY76687) or  Escherichia coli  (NP_416714, NP_417703). The pyruvate phosphate dikinase (PPDK) may be, for example, from  Clostridium autoethanogenum  (AGY76274, AGY77114). The PEP carboxykinase (PCK) may be, for example, from  Clostridium autoethanogenum  (AGY76928) or  Escherichia coli  (NP_417862). The fumarate hydratase/fumerase may be, for example, from  Clostridium autoethanogenum  (AGY76121, AGY76122) or  Escherichia coli  (NP_416128, NP_416129, NP_418546). The fumarate reductase/succinate dehydrogenase may be, for example, from  Clostridium autoethanogenum  (AGY74573, AGY74575, AGY75257, AGY77166) or  Escherichia coli  (NP_415249, NP_415250, NP_415251, NP_415252, NP_418575, NP_418576, NP_418577, NP_418578). The succinyl-CoA synthetase may be, for example, from  Escherichia coli  (NP_415256, NP_415257). 
     Step 22 shows the conversion of acetyl-CoA and succinyl-CoA to 3-oxo-adipyl-CoA. This step may be catalyzed by β-ketoadipyl-CoA thiolase (EC 2.3.1.16). The ketoisovalerate oxidoreductase may be, for example, PaaJ from  Escherichia coli  (WP_001206190.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 23 shows the conversion of 3-oxo-adipyl-CoA to 3-hydroxyadipyl-CoA. This step may be catalyzed by 3-hydroxybutyryl-CoA dehydrogenase (EC 1.1.1.157) or acetoacetyl-CoA hydratase (EC 4.2.1.119). The 3-hydroxybutyryl-CoA dehydrogenase or acetoacetyl-CoA hydratase may be, for example, Hbd from  Clostridium beijerinckii  (WP_011967675.1) (SEQ ID NO: 55), Hbd from  Clostridium acetobutylicum  (NP_349314.1) (SEQ ID NO: 56), Hbd1 from  Clostridium kluyveri  (WP_011989027.1) (SEQ ID NO: 57), or PaaH1 from  Cupriavidus necator  (WP_010814882.1). Of note, PhaB is R-specific and Hbd is S-specific. Additionally, Hbd1 from  Clostridium kluyveri  is NADPH-dependent and Hbd from  Clostridium acetobutylicum  and  Clostridium beijerinckii  are NADH-dependent.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 24 shows the conversion of 3-hydroxyadipyl-CoA to 2,3-dehydroadipyl-CoA. This step may be catalyzed by an enoyl-CoA hydratase (EC: 4.2.1.17) or enoyl-CoA reductase (EC: 1.3.1.38). The enoyl-CoA hydratase or enoyl-CoA reductase may be, for example, Crt from  C. acetobutylicum  (NP_349318.1) or PhaJ from  Aeromonas caviae  (032472) (Seq. ID No. 52).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 25 shows the conversion of 2,3-dehydroadipyl-CoA to adipyl-CoA. This step may be catalyzed by trans-2-enoyl-CoA reductase (EC 1.3.8.1, EC 1.3.1.86, EC 1.3.1.85, EC 1.3.1.44). The trans-2-enoyl-CoA reductase may be, for example, Bcd from  C. acetobutylicum  (NP_349317.1) that forms a complex with electron flavoproteins EtfAB (NP_349315, NP_349316), Ccr from  Streptomyces collinus  (AAA92890), Ccr from  Rhodobacter sphaeroides  (YP_354044.1), Ter from  Treponema denticola  (NP_971211.1), or Ter from  Euglena gracilis  (AY741582.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 26 shows the conversion of adipyl-CoA to adipic acid. This step may be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 27 shows the conversion of shows the conversion of 3-hydroxbutyryl-CoA to crotonyl-CoA. This step may be catalyzed by a crotonyl-CoA hydratase (crotonase) (EC 4.2.1.17) or crotonyl-CoA reductase (EC 1.3.1.38). The crotonyl-CoA hydratase (crotonase) or crotonyl-CoA reductase may be, for example, Crt from  C. acetobutylicum  (NP_349318.1) (SEQ ID NO: 52) or PhaJ from  Aeromonas caviae  (032472).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 28 shows the conversion of crotonyl-CoA to crotonate. This step may be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 29 shows the conversion of crotonate to crotonaldehyde. This step may be catalyzed by aldehyde:ferredoxin oxidoreductase (EC 1.2.7.5). Exemplary sources for aldehyde:ferredoxin oxidoreductases are described elsewhere in this application. AOR catalyzes the reaction of an acid and reduced ferredoxin to form an aldehyde and oxidized ferredoxin. In acetogens, this reaction can be coupled to oxidation CO (via CO dehydrogenase, EC 1.2.7.4) or hydrogen (via ferredoxin-dependent hydrogenase, EC 1.12.7.2 or 1.12.1.4) that both yield reduced ferredoxin (Köpke,  Curr Opin Biotechnol  22: 320-325, 2011; Köpke,  PNAS USA,  107: 13087-13092, 2010).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous AOR or introduction of an exogenous AOR in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields. AOR of  Pyrococcus furiosus  has been demonstrated activity converting crotonaldehyde and crotonate (Loes,  J Bacteriol,  187: 7056-7061, 2005). Alternatively, exogenous AOR may be introduced into a microorganism that does not natively comprise AOR, e.g.,  E. coli . In particular, the co-expression of Ptb-Buk and AOR (and, optionally, Adh) may enable such a microorganism to produce new non-native products. 
     Step 30 shows the conversion of crotonaldehyde to 2-buten-1-ol. This step may be catalyzed by alcohol dehydrogenase (EC 1.1.1.1. or 1.1.1.2.). Alcohol dehydrogenase can convert an aldehyde and NAD(P)H to an alcohol and NAD(P). The alcohol dehydrogenase may be, for example, Adh from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 67),  Clostridium ljungdahlii  (ADK17019.1) (SEQ ID NO: 68), or  Clostridium ragsdalei , BdhB from  Clostridium acetobutylicum  (NP_349891.1) (SEQ ID NO: 69), Bdh from  Clostridium beijerinckii  (WP_041897187.1) (SEQ ID NO: 70), Bdh1 from  Clostridium ljungdahlii  (YP_003780648.1) (SEQ ID NO: 71), Bdh1 from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 72), Bdh2 from  Clostridium ljungdahlii  (YP_003782121.1) (SEQ ID NO: 73), Bdh2 from  Clostridium autoethanogenum  (AGY74784.1) (SEQ ID NO: 74), AdhE1 from  Clostridium acetobutylicum  (NP_149325.1) (SEQ ID NO: 75), AdhE2 from  Clostridium acetobutylicum  (NP_149199.1) (SEQ ID NO: 76), AdhE from  Clostridium beijerinckii  (WP_041893626.1) (SEQ ID NO: 77), AdhE1 from  Clostridium autoethanogenum  (WP_023163372.1) (SEQ ID NO: 78), or AdhE2 from  Clostridium autoethanogenum  (WP_023163373.1) (SEQ ID NO: 79).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous alcohol dehydrogenase or introduction of an exogenous alcohol dehydrogenase in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields.  Escherichia coli  likely does not have native activity for this step. 
     Step 31 shows the conversion of crotonyl-CoA to butyryl-CoA. This step may be catalyzed by butyryl-CoA dehydrogenase or trans-2-enoyl-CoA reductase (EC 1.3.8.1, EC 1.3.1.86, EC 1.3.1.85, EC 1.3.1.44). The butyryl-CoA dehydrogenase or trans-2-enoyl-CoA reductase may be, for example, Bcd from  C. acetobutylicum  (NP_349317.1) that forms a complex with electron flavoproteins EtfAB (NP_349315, NP_349316), Ccr from  Streptomyces collinus  (AAA92890), Ccr from  Rhodobacter sphaeroides  (YP_354044.1), Ter from  Treponema denticola  (NP_971211.1), or Ter from  Euglena gracilis  (AY741582.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 32 shows the conversion of butyryl-CoA to acetobutyryl-CoA. This step may be catalyzed by thiolase or acyl-CoA acetyltransferase (EC 2.3.1.9). The thiolase may be, for example, ThlA from  Clostridium acetobutylicum  (WP_010966157.1) (SEQ ID NO: 1), ThlA1 from  Clostridium kluyveri  (EDK35681), ThlA2 from  Clostridium kluyveri  (EDK35682), ThlA3 from  Clostridium kluyveri  (EDK35683), PhaA from  Cupriavidus necator  (WP_013956452.1) (SEQ ID NO: 2), BktB from  Cupriavidus necator  (WP_011615089.1) (SEQ ID NO: 3), or AtoB from  Escherichia coli  (NP_416728.1) (SEQ ID NO: 4).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  has native activity for this step. 
     Step 33 shows the conversion of acetobutyryl-CoA to acetobutyrate. This step may be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 34 shows the conversion of acetobutyrate to acetylacetone. This step may be catalyzed by an acetoacetate decarboxylase (EC 4.1.1.4). The acetoacetate decarboxylase may be, for example, Adc from  Clostridium beijerinckii  (WP_012059998.1) (SEQ ID NO: 14). This step may also be catalyzed by an alpha-ketoisovalerate decarboxylase (EC 4.1.1.74). The alpha-ketoisovalerate decarboxylase may be, for example, KivD from  Lactococcus lactis  (SEQ ID NO: 15).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step. Additionally,  Escherichia coli  does not have known native activity for this step. Rarely, conversion of acetoacetate to acetone may occur spontaneously. However, spontaneous conversion is highly inefficient and unlikely to result in the production of downstream products at desirable levels. 
     Step 35 shows the conversion of acetylacetone to 3-methyl-2-butanol. This step may be catalyzed by a primary:secondary alcohol dehydrogenase (EC 1.1.1.2). The primary:secondary alcohol dehydrogenase may be, for example, SecAdh from  Clostridium autoethanogenum  (AGY74782.1) (SEQ ID NO: 16), SecAdh from  Clostridium ljungdahlii  (ADK15544.1) (SEQ ID NO: 17), SecAdh from  Clostridium ragsdalei  (WP_013239134.1) (SEQ ID NO: 18), or SecAdh from  Clostridium beijerinckii  (WP_026889046.1) (SEQ ID NO: 19). This step may also be catalyzed by a primary:secondary alcohol dehydrogenase (EC 1.1.1.80), such as SecAdh from  Thermoanaerobacter brokii  (3FSR_A) (SEQ ID NO: 20).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step (Köpke,  Appl Environ Microbiol,  80: 3394-3403, 2014). However,  Escherichia coli  does not have known native activity for this step. Knocking down or knocking out this enzyme in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  results in the production and accumulation of acetylacetone rather than 3-methyl-2-butanol (WO 2015/085015). 
     Step 36 shows the conversion of acetobutyryl-CoA to 3-hydroxyhexanoyl-CoA. This step may be catalyzed by 3-hydroxybutyryl-CoA dehydrogenase (EC 1.1.1.157) or acetoacetyl-CoA hydratase (EC 4.2.1.119). The 3-hydroxybutyryl-CoA dehydrogenase or acetoacetyl-CoA hydratase may be, for example, Hbd from  Clostridium beijerinckii  (WP_011967675.1) (SEQ ID NO: 55), Hbd from  Clostridium acetobutylicum  (NP_349314.1) (SEQ ID NO: 56), Hbd1 from  Clostridium kluyveri  (WP_011989027.1) (SEQ ID NO: 57), Hbd2 from  Clostridium kluyveri  (EDK34807), or PaaH1 from  Cupriavidus necator  (WP_010814882.1). Of note, PhaB is R-specific and Hbd is S-specific. Additionally, Hbd1 from  Clostridium kluyveri  is NADPH-dependent and Hbd from  Clostridium acetobutylicum  and  Clostridium beijerinckii  are NADH-dependent.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 37 shows the conversion of 3-hydroxyhexanoyl-CoA to 3-hydroxyhexanoate. This step may be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 38 shows the conversion of 3-hydroxyhexanoate to 1,3-hexaldehyde. This step may be catalyzed by aldehyde:ferredoxin oxidoreductase (EC 1.2.7.5). Exemplary sources for aldehyde:ferredoxin oxidoreductases are described elsewhere in this application. AOR catalyzes the reaction of an acid and reduced ferredoxin to form an aldehyde and oxidized ferredoxin. In acetogens, this reaction can be coupled to oxidation CO (via CO dehydrogenase, EC 1.2.7.4) or hydrogen (via ferredoxin-dependent hydrogenase, EC 1.12.7.2 or 1.12.1.4) that both yield reduced ferredoxin (Köpke, Curr Opin Biotechnol 22: 320-325, 2011; Köpke,  PNAS  USA, 107: 13087-13092, 2010).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous AOR or introduction of an exogenous AOR in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields. Alternatively, exogenous AOR may be introduced into a microorganism that does not natively comprise AOR, e.g.,  E. coli . In particular, the co-expression of Ptb-Buk and AOR (and, optionally, Adh) may enable such a microorganism to produce new non-native products. 
     Step 39 shows the conversion of 1,3-hexaldehyde to 1,3-hexanediol. This step may be catalyzed by alcohol dehydrogenase (EC 1.1.1.1. or 1.1.1.2.). Alcohol dehydrogenase can convert an aldehyde and NAD(P)H to an alcohol and NAD(P). The alcohol dehydrogenase may be, for example, Adh from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 67),  Clostridium ljungdahlii  (ADK17019.1) (SEQ ID NO: 68), or  Clostridium ragsdalei , BdhB from  Clostridium acetobutylicum  (NP_349891.1) (SEQ ID NO: 69), Bdh from  Clostridium beijerinckii  (WP_041897187.1) (SEQ ID NO: 70), Bdh1 from  Clostridium ljungdahlii  (YP_003780648.1) (SEQ ID NO: 71), Bdh1 from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 72), Bdh2 from  Clostridium ljungdahlii  (YP_003782121.1) (SEQ ID NO: 73), Bdh2 from  Clostridium autoethanogenum  (AGY74784.1) (SEQ ID NO: 74), AdhE1 from  Clostridium acetobutylicum  (NP_149325.1) (SEQ ID NO: 75), AdhE2 from  Clostridium acetobutylicum  (NP_149199.1) (SEQ ID NO: 76), AdhE from  Clostridium beijerinckii  (WP_041893626.1) (SEQ ID NO: 77), AdhE1 from  Clostridium autoethanogenum  (WP_023163372.1) (SEQ ID NO: 78), or AdhE2 from  Clostridium autoethanogenum  (WP_023163373.1) (SEQ ID NO: 79).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous alcohol dehydrogenase or introduction of an exogenous alcohol dehydrogenase in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields.  Escherichia coli  likely does not have native activity for this step. 
     Step 40 shows the conversion of acetoacetyl-CoA to 3-hydroxy-3-methylglutaryl-CoA. This step may be catalyzed by a hydroxymethylglutaryl-CoA synthase (HMG-CoA synthase) (EC 2.3.3.10). HMG-CoA synthases are widespread across many genera and kingdoms of life and include, e.g., MvaS from  Staphylococcus aureus  (WP_053014863.1), ERG13 from  Saccharomyces cerevisiae  (NP_013580.1), HMGCS2 from  Mus musculus  (NP_032282.2), and many other members of the EC 2.3.3.10 group of enzymes.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 41 shows the conversion of 3-hydroxy-3-methylglutanoyl-CoA to 3-methylgluconyl-CoA. This step may be catalyzed by a 3-hydroxybutyryl-CoA dehydratase (EC 4.2.1.55). The 3-hydroxybutyryl-CoA dehydratase may be, for example, LiuC from  Myxococcus xanthus  (WP_011553770.1). This step may also be catalyzed by a short-chain-enoyl-CoA hydratase (EC 4.2.1.150) or an enoyl-CoA hydratase (EC 4.2.1.17).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 42 shows the conversion of 3-methylgluconyl-CoA to 2-methylcrotonyl-CoA. This step may be catalyzed by a methylcrotonyl-CoA decarboxylase (with high structural similarity to glutaconate-CoA transferase (EC 2.8.3.12)), e.g., aibAB from  Myxococcus xanthus  (WP_011554267.1 and WP_011554268.1). This step may also be catalyzed by a methylcrotonoyl-CoA carboxylase (EC 6.4.1.4), e.g., LiuDB from  Pseudomonas aeruginosa  (NP_250702.1 and NP_250704.1) or MCCA and MCCB from  Arabidopsis thaliana  (NP_563674.1 and NP_567950.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 43 shows the conversion of methylcrotonyl-CoA to isovaleryl-CoA. This step may be catalyzed by an oxidoreductase, zinc-binding dehydrogenase. This oxidoreductase, zinc-binding dehydrogenase may be, for example, AibC from  Myxococcus xanthus  (WP_011554269.1).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not have known native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Step 44 shows the conversion of isovaleryl-CoA to isovalerate. This step may be catalyzed by CoA-transferase (i.e., acetyl-CoA:acetoacetyl-CoA transferase) (EC 2.8.3.9). The CoA-transferase may be, for example, CtfAB, a heterodimer comprising subunits CtfA and CtfB, from  Clostridium beijerinckii  (CtfA, WP_012059996.1) (SEQ ID NO: 5) (CtfB, WP_012059997.1) (SEQ ID NO: 6). This step may also be catalyzed by thioesterase (EC 3.1.2.20). The thioesterase may be, for example, TesB from  Escherichia coli  (NP_414986.1) (SEQ ID NO: 7). This step may also be catalyzed by a putative thioesterase, e.g., from  Clostridium autoethanogenum  or  Clostridium ljungdahlii . In particular, three putative thioesterases have been identified in  Clostridium autoethanogenum : (1) “thioesterase 1” (AGY74947.1; annotated as palmitoyl-CoA hydrolase; SEQ ID NO: 8), (2) “thioesterase 2” (AGY75747.1; annotated as 4-hydroxybenzoyl-CoA thioesterase; SEQ ID NO: 9), and (3) “thioesterase 3” (AGY75999.1; annotated as putative thioesterase; SEQ ID NO: 10). Three putative thioesterases have also been identified in  Clostridium ljungdahlii : (1) “thioesterase 1” (ADK15695.1; annotated as predicted acyl-CoA thioesterase 1; SEQ ID NO: 11), (2) “thioesterase 2” (ADK16655.1; annotated as predicted thioesterase; SEQ ID NO: 12), and (3) “thioesterase 3” (ADK16959.1; annotated as predicted thioesterase; SEQ ID NO: 13). This step may also be catalyzed by phosphate butyryltransferase (EC 2.3.1.19)+butyrate kinase (EC 2.7.2.7). Exemplary sources for phosphate butyryltransferase and butyrate kinase are described elsewhere in this application. Native enzymes in  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (or  Escherichia coli ), such as thioesterases from  Clostridium autoethanogenum , may catalyze this step and result in the production of some amount of downstream products. However, introduction of an exogenous enzyme or overexpression of an endogenous enzyme may be required to produce downstream products at desirable levels. Additionally, in certain embodiments, a disruptive mutation may be introduced to an endogenous enzyme, such as an endogenous thioesterase, to reduce or eliminate competition with introduced Ptb-Buk. 
     Step 45 shows the conversion of isovalerate to isovaleraldehyde. This step may be catalyzed by aldehyde:ferredoxin oxidoreductase (EC 1.2.7.5). The aldehyde:ferredoxin oxidoreductase (AOR) may be, for example, AOR from  Clostridium autoethanogenum  (WP_013238665.1; WP 013238675.1) (SEQ ID NOs: 63 and 64, respectively) or AOR from  Clostridium ljungdahlii  (ADK15073.1; ADK15083.1) (SEQ ID NOs: 65 and 66, respectively). Further exemplary sources for aldehyde:ferredoxin oxidoreductases are described elsewhere in this application.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous AOR or introduction of an exogenous AOR in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields. Alternatively, exogenous AOR may be introduced into a microorganism that does not natively comprise AOR, e.g.,  E. coli . In particular, the co-expression of Ptb-Buk and AOR (and, optionally, Adh) may enable such a microorganism to produce new non-native products. 
     Step 46 shows the conversion of isovaleraldehyde to isoamyl alcohol. This step may be catalyzed by alcohol dehydrogenase (EC 1.1.1.1. or 1.1.1.2.). Alcohol dehydrogenase can convert an aldehyde and NAD(P)H to an alcohol and NAD(P). The alcohol dehydrogenase may be, for example, Adh from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 67),  Clostridium ljungdahlii  (ADK17019.1) (SEQ ID NO: 68), or  Clostridium ragsdalei , BdhB from  Clostridium acetobutylicum  (NP_349891.1) (SEQ ID NO: 69), Bdh from  Clostridium beijerinckii  (WP_041897187.1) (SEQ ID NO: 70), Bdh1 from  Clostridium ljungdahlii  (YP_003780648.1) (SEQ ID NO: 71), Bdh1 from  Clostridium autoethanogenum  (AGY76060.1) (SEQ ID NO: 72), Bdh2 from  Clostridium ljungdahlii  (YP_003782121.1) (SEQ ID NO: 73), Bdh2 from  Clostridium autoethanogenum  (AGY74784.1) (SEQ ID NO: 74), AdhE1 from  Clostridium acetobutylicum  (NP_149325.1) (SEQ ID NO: 75), AdhE2 from  Clostridium acetobutylicum  (NP_149199.1) (SEQ ID NO: 76), AdhE from  Clostridium beijerinckii  (WP_041893626.1) (SEQ ID NO: 77), AdhE1 from  Clostridium autoethanogenum  (WP_023163372.1) (SEQ ID NO: 78), or AdhE2 from  Clostridium autoethanogenum  (WP_023163373.1) (SEQ ID NO: 79).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  have native activity for this step. However, overexpression of endogenous alcohol dehydrogenase or introduction of an exogenous alcohol dehydrogenase in  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  may be desirable to enhance product yields.  Escherichia coli  likely does not have native activity for this step. 
     Step 47 shows the conversion of isovaleryl-CoA to isovaleraldehyde. This step may be catalyzed by butyraldehyde dehydrogenase (EC 1.2.1.57). The butyraldehyde dehydrogenase may be, for example, Bld from  Clostridium saccharoperbutylacetonicum  (AAP42563.1) (SEQ ID NO: 80).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  likely do not have native activity for this step.  Escherichia coli  does not have known native activity for this step. 
     Overview of Ptb-Buk 
     The invention provides new pathways utilizing the Ptb-Buk enzyme system. In nature, this enzyme system is found in a range of butyrate producing microorganisms, such as butyrate-producing  Clostridia  or  Butyrivibrio . In particular, phosphate butyryltransferase (Ptb) (EC 2.3.1.19) natively catalyzes the reaction of butanoyl-CoA+phosphate to form CoA+butanoyl phosphate and butyrate kinase (Buk) (EC 2.7.2.7) natively catalyzes the reaction of butanoyl phosphate and ADP to form butyrate (butanoate) and ATP. Accordingly, these enzymes together (Ptb-Buk) natively catalyze the conversion of butanoyl-CoA to butyrate and generate one ATP via substrate level-phosphorylation ( FIG. 2 ). However, the inventors have discovered that Ptb is promiscuous and is capable of accepting a variety of acyl-CoAs and enoyl-CoAs as substrates, such that Ptb-Buk may be used to convert a number of acyl-CoAs and enoyl-CoAs to their corresponding acids or alkenates, respectively, while simultaneously generating ATP. It has been reported Ptb is active on a range of acyl-CoAs including acetoacetyl-CoA, in vitro (Thompson,  Appl Environ Microbiol,  56: 607-613, 1990). It has not previously been shown that acetoacetyl-phosphate could be a substrate for Buk. Although Buk is known to accept a broad substrate range (Liu,  Appl Microbiol Biotechnol,  53: 545-552, 2000), no activity has been shown in vivo. 
     Additionally, the inventors have discovered that the introduction of exogenous Ptb-Buk enables certain microorganisms to produce useful products, including acetone, isopropanol, isobutylene, 3-hydroxybutyrate, 1,3-butanediol, and 2-hydroxyisobutyrate, as well as other products such as propionate, caproate, and octonate. 
     New pathways that rely on Ptb-Buk offer several major advantages over other known and existing pathway routes for production of products that rely on a CoA-transferase—as in the classic  Clostridial  acetone-butanol-ethanol (ABE) fermentation pathway—or a thioesterase (Jones,  Microbiol Rev,  50: 484-524, 1986; Matsumoto,  Appl Microbiol Biotechnol,  97: 205-210, 2013; May,  Metabol Eng,  15: 218-225, 2013) ( FIG. 3 ). In particular, these new pathways (1) are not dependent on the presence or production of particular molecules, such as organic acids, e.g., butyrate or acetate, required for the CoA-transferase reaction and (2) allow for generation of ATP via substrate level phosphorylation that would not be conserved in a thioesterase or CoA-transferase reaction. The same advantages also apply when using the Ptb-Buk system for other reactions, such as the conversion of 3-hydroxybutyryl-CoA to 3-hydroxybutyrate. Thus, these new pathways have the potential to yield much higher production titers and rates by generating additional energy and producing target products without co-production of undesired byproducts, such as acetate. 
     Particularly on a commercial scale, it is not desirable for microorganisms to produce acetate (or other organic acids required for the CoA transferase reaction) as byproduct, since acetate diverts carbon away from target products and thus affects the efficiency and yield of target products. Additionally, acetate may be toxic to microorganisms and/or may serve as a substrate for the growth of contaminating microorganisms. Furthermore, the presence of acetate makes it more difficult to recover and separate target products and to control fermentation conditions to favor the production of target products. 
     ATP generation through substrate level phosphorylation can be used as a driving force for product synthesis, especially in ATP-limited systems. In particular, acetogenic bacteria are known to live on the thermodynamic edge of life (Schuchmann,  Nat Rev Microbiol,  12: 809-821, 2014). As such, all acetogenic microorganisms isolated to date have been described to produce acetate (Drake, Acetogenic Prokaryotes, In:  The Prokaryotes,  3 rd  edition, pages 354-420, New York, N.Y., Springer, 2006) since the production of acetate provides the microorganism with an option to directly generate ATP from substrate level phosphorylation via Pta (phosphotransacetylase) (EC 2.3.1.8) and Ack (acetate kinase) (EC 2.7.2.1). Although mechanisms such as membrane gradients and electro bifurcation enzymes coupled to ion or proton translocating systems, e.g., the Rnf complex (Schuchmann,  Nat Rev Microbiol,  12: 809-821, 2014), conserve ATP in these microorganisms, direct ATP generation remains critical for their survival. As a result, when introducing heterologous pathways that do not allow for ATP generation, acetate is produced as a byproduct (Schiel-Bengelsdorf,  FEBS Lett,  586: 2191-2198, 2012). The Ptb-Buk pathways described herein, however, provide an alternative mechanism for the microorganism to generate ATP via substrate level phosphorylation and, therefore, avoid acetate production. In particular, acetate-forming enzymes, such as Pta-Ack, that would otherwise be essential (Nagarajan,  Microb Cell Factories,  12: 118, 2013) can be replaced with Ptb-Buk as an alternative means of ATP generation. Since the microorganism can then rely on ATP generation via Ptb-Buk, this system provides a driving force that ensures maximum flux through the new pathways that use Ptb-Buk. The generation of ATP may also be crucial for downstream pathways that require ATP. For example, fermentative production of isobutylene from acetone requires ATP. While the complete pathway from acetyl-CoA to isobutylene is ATP-consuming when using a CoA-transferase or a thioesterase, the pathway is energy neutral when using Ptb-Buk. 
     Exemplary sources for Ptb and Buk are provided. However, it should be appreciated that other suitable sources for Ptb and Buk may be available. Additionally, Ptb and Buk may be engineered to improve activity and/or genes encoding Ptb-Buk may be codon-optimized for expression in particular host microorganisms. 
     The phosphate butyryltransferase may be or may be derived, for example, from any of the following sources, the sequences of which are publically available: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Description 
                 Microorganism 
                 Accession 
               
               
                   
               
             
            
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 EKQ52186 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_009167896 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium saccharoperbutylacetonicum 
                 
                 WP_015390396 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium saccharobutylicum 
                 
                 WP_022743598 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium beijerinckii 
                 
                 WP_026886639 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium beijerinckii 
                 
                 WP_041893500 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium butyricum 
                 
                 WP_003410761 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CDB14331 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_049180512 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CDB74819 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium paraputrificum 
                 
                 WP_027098882 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_024615655 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium celatum 
                 
                 WP_005211129 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium baratii 
                 
                 WP_039312969 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium intestinale 
                 
                 WP_021800215 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_042402499 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_032117069 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium perfringens 
                 
                 ABG85761 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_003374233 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium perfringens 
                 
                 WP_004460499 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium perfringens 
                 
                 WP_003454254 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium perfringens 
                 
                 WP_041707926 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium perfringens 
                 
                 BAB82054 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_008681116 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium chauvoei 
                 
                 WP_021876993 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium colicanis 
                 
                 WP_002598839 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium cadaveris 
                 
                 WP_027637778 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium acetobutylicum 
                 
                 WP_010966357 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium pasteurianum 
                 
                 WP_015617430 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium arbusti 
                 
                 WP_010238988 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium pasteurianum 
                 
                 WP_003445696 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium scatologenes 
                 
                 WP_029160341 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_032120461 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium drakei 
                 
                 WP_032078800 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_021281241 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium argentinense 
                 
                 WP_039635970 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium akagii 
                 
                 WP_026883231 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_053242611 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium carboxidivorans 
                 
                 WP_007063154 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_035292411 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium sulfidigenes 
                 
                 WP_035133394 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium tetanomorphum 
                 
                 WP_035147564 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium hydrogeniformans 
                 
                 WP_027633206 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_040212965 
               
               
                 phosphate butyryltransferase 
                 
                   Candidatus Clostridium 
                 
                 WP_040327613 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_040192242 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_050606427 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium lundense 
                 
                 WP_027625137 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium algidicarnis 
                 
                 WP_029451333 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_035306567 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium acetobutylicum 
                 
                 AAA75486 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_025775938 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_045541062 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_003357252 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_030037192 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium bornimense 
                 
                 WP_044039341 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_041346554 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_053468896 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridiales bacterium 
                 
                 WP_034572261 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium tetani 
                 
                 WP_023439553 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridiales bacterium 
                 
                 ERI95297 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium botulinum 
                 
                 WP_047403027 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium tetani 
                 
                 WP_011100667 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium tetani 
                 
                 WP_035111554 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium senegalense 
                 
                 WP_010295062 
               
               
                 phosphate butyryltransferase 
                   Caloramator  sp. 
                 WP_027307587 
               
               
                 phosphate butyryltransferase 
                 
                   Thermobrachium celere 
                 
                 WP_018661036 
               
               
                 phosphate butyryltransferase 
                 
                   Clostridium cellulovorans 
                 
                 WP_010073683 
               
               
                 phosphate butyryltransferase 
                 
                   Coprococcus comes 
                 
                 CDB84786 
               
               
                 phosphate butyryltransferase 
                 
                   Coprococcus comes 
                 
                 WP_008371924 
               
               
                 phosphate butyryltransferase 
                   Eubacterium  sp. 
                 CCZ03827 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CCZ05442 
               
               
                 phosphate butyryltransferase 
                 
                   Caloramator australicus 
                 
                 WP_008907395 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CCY59505 
               
               
                 phosphate butyryltransferase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_035626368 
               
               
                 phosphate butyryltransferase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_027440767 
               
               
                 phosphate butyryltransferase 
                 
                   Fervidicella metallireducens 
                 
                 WP_035381340 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CCX89274 
               
               
                 phosphate butyryltransferase 
                 
                   Eubacterium xylanophilum 
                 
                 WP_026834525 
               
               
                 phosphate butyryltransferase 
                   Roseburia  sp. 
                 CDF44203 
               
               
                 phosphate butyryltransferase 
                 
                   Butyrivibrio crossotus 
                 
                 WP_005600912 
               
               
                 phosphate butyryltransferase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_027117626 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CDA68345 
               
               
                 phosphate butyryltransferase 
                 
                   Peptostreptococcaceae bacterium 
                 
                 WP_026899905 
               
               
                 phosphate butyryltransferase 
                 
                   Butyrivibrio crossotus 
                 
                 CCY77124 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 CDE44914 
               
               
                 phosphate butyryltransferase 
                 
                   Coprococcus eutactus 
                 
                 WP_004853197 
               
               
                 phosphate butyryltransferase 
                 
                   Firmicutes bacterium 
                 
                 CCY23248 
               
               
                 phosphate butyryltransferase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_027111007 
               
               
                 phosphate butyryltransferase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_016293387 
               
               
                 phosphate butyryltransferase 
                   Clostridium  sp. 
                 WP_046822491 
               
               
                   
               
            
           
         
       
     
     In a preferred embodiment, the phosphate butyryltransferase is Ptb from  Clostridium acetobutylicum  (WP_010966357; SEQ ID NO: 87) or  Clostridium beijerinckii  (WP_026886639; SEQ ID NO: 88) (WP_041893500; SEQ ID NO: 89).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not natively contain phosphate butyryltransferase. 
     The butyrate kinase may be or may be derived, for example, from any of the following sources, the sequences of which are publically available: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Description 
                 Microorganism 
                 Accession 
               
               
                   
               
             
            
               
                 butyrate kinase 
                 
                   Clostridium pasteurianum 
                 
                 ALB48406 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 CDB14330 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 CDB74820 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 EKQ52187 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 Q0SQK0 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_002582660 
               
               
                 butyrate kinase 
                 
                   Clostridium colicanis 
                 
                 WP_002598838 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_003371719 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 WP_003454444 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 WP_004459180 
               
               
                 butyrate kinase 
                 
                   Clostridium celatum 
                 
                 WP_005211128 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_008681112 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_008681114 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_009167897 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 WP_011010889 
               
               
                 butyrate kinase 
                 
                   Clostridium beijerinckii 
                 
                 WP_011967556 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_012422882 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_012450845 
               
               
                 butyrate kinase 
                 
                   Clostridium saccharoper- 
                 
                 WP_015390397 
               
               
                   
                 
                   butylacetonicum 
                 
                   
               
               
                 butyrate kinase 
                 
                   Clostridium beijerinckii 
                 
                 WP_017209677 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_017825911 
               
               
                 butyrate kinase 
                 
                   Clostridium chauvoei 
                 
                 WP_021876994 
               
               
                 butyrate kinase 
                 
                   Clostridium saccharobutylicum 
                 
                 WP_022743599 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_024615656 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 WP_025648345 
               
               
                 butyrate kinase 
                 
                   Clostridium beijerinckii 
                 
                 WP_026886638 
               
               
                 butyrate kinase 
                 
                   Clostridium paraputrificum 
                 
                 WP_027098883 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_032117070 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_035786166 
               
               
                 butyrate kinase 
                 
                   Clostridium baratii 
                 
                 WP_039312972 
               
               
                 butyrate kinase 
                 
                   Clostridium diolis 
                 
                 WP_039772701 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_041082388 
               
               
                 butyrate kinase 
                 
                   Clostridium beijerinckii 
                 
                 WP_041893502 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_042402497 
               
               
                 butyrate kinase 
                 
                   Clostridium baratii 
                 
                 WP_045725505 
               
               
                 butyrate kinase 
                 
                   Clostridium perfringens 
                 
                 WP_049039634 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_049180514 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_053341511 
               
               
                 butyrate kinase 
                 
                   Clostridium butyricum 
                 
                 ABU40948 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 CDE44915 
               
               
                 butyrate kinase 
                 
                   Clostridium senegalense 
                 
                 WP_010295059 
               
               
                 butyrate kinase 
                 
                   Clostridium intestinale 
                 
                 WP_021800216 
               
               
                 butyrate kinase 
                 
                   Eubacterium ventriosum 
                 
                 WP_005363839 
               
               
                 butyrate kinase 
                 
                   Clostridiales bacterium 
                 
                 WP_021657038 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_021281242 
               
               
                 butyrate kinase 
                 
                   Clostridium sporogenes 
                 
                 WP_045520059 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_050606428 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_012048334 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_012343352 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_003401518 
               
               
                 butyrate kinase 
                 
                   Clostridium argentinense 
                 
                 WP_039635972 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_003357547 
               
               
                 butyrate kinase 
                 
                   Clostridium hydrogeniformans 
                 
                 WP_027633205 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_033066487 
               
               
                 butyrate kinase 
                   Roseburia  sp. 
                 CDF44202 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_027111008 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 CDA68344 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_022782491 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_012101111 
               
               
                 butyrate kinase 
                 
                   Clostridium carboxidivorans 
                 
                 WP_007063155 
               
               
                 butyrate kinase 
                 
                   Clostridium botulinum 
                 
                 WP_041346556 
               
               
                 butyrate kinase 
                 
                   Clostridium drakei 
                 
                 WP_032078801 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_032120462 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_053468897 
               
               
                 butyrate kinase 
                 
                   Firmicutes bacterium 
                 
                 CCZ27888 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_035306569 
               
               
                 butyrate kinase 
                 
                   Coprococcus comes 
                 
                 CDB84787 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_035292410 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 CCX89275 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_040212963 
               
               
                 butyrate kinase 
                 
                   Clostridium pasteurianum 
                 
                 WP_003445697 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_053242610 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_016299320 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_022785085 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_016281561 
               
               
                 butyrate kinase 
                   Eubacterium  sp. 
                 CDA28786 
               
               
                 butyrate kinase 
                 
                   Clostridium scatologenes 
                 
                 WP_029160342 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_016228168 
               
               
                 butyrate kinase 
                 
                   Clostridium pasteurianum 
                 
                 WP_015617429 
               
               
                 butyrate kinase 
                 
                   Clostridium algidicarnis 
                 
                 WP_029451332 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_016293388 
               
               
                 butyrate kinase 
                 
                   Clostridium sulfidigenes 
                 
                 WP_035133396 
               
               
                 butyrate kinase 
                 
                   Clostridium tetani 
                 
                 WP_011100666 
               
               
                 butyrate kinase 
                 
                   Clostridium tetanomorphum 
                 
                 WP_035147567 
               
               
                 butyrate kinase 
                 
                   Subdoligranulum variabile 
                 
                 WP_007045828 
               
               
                 butyrate kinase 
                   Eubacterium  sp. 
                 CCZ03826 
               
               
                 butyrate kinase 
                 
                   Firmicutes bacterium 
                 
                 CDF07483 
               
               
                 butyrate kinase 
                   Eubacterium  sp. 
                 CDB13677 
               
               
                 butyrate kinase 
                   Clostridium  sp. 
                 WP_008400594 
               
               
                 butyrate kinase 
                 
                   Clostridium tetani 
                 
                 WP_023439552 
               
               
                 butyrate kinase 
                 
                   Clostridiales bacterium 
                 
                 WP_022787536 
               
               
                 butyrate kinase 
                 
                   Lachnospiraceae bacterium 
                 
                 WP_027434709 
               
               
                 butyrate kinase 
                 
                   Firmicutes bacterium 
                 
                 CCY23249 
               
               
                 butyrate kinase 
                 
                   Clostridium acetobutylicum 
                 
                 WP_010966356 
               
               
                   
               
            
           
         
       
     
     In a preferred embodiment, the butyrate kinase is Buk from  Clostridium acetobutylicum  (WP_010966356; SEQ ID NO: 90) or  Clostridium beijerinckii  (WP_011967556; SEQ ID NO: 91) (WP_017209677; SEQ ID NO: 92) (WP_026886638; SEQ ID NO: 93) (WP_041893502; SEQ ID NO: 94).  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  do not natively contain butyrate kinase. 
     Since Ptb-Buk has been shown to function on a broad range of substrates it is reasonable to assume that if Ptb-Buk does not exhibit any activity and a desired substrate it can be engineered to achieve activity on the substrate in question. A strategy could be (but would not be limited to) rational design based on available crystal structures of Ptb and Buk with and without a bound substrate where the binding pocket would be changed to accommodate the new substrate or through saturation mutagenesis. When activity is obtained, it can be further improved through iterative cycles of enzyme engineering. These engineering efforts would be combined with assays to test enzyme activity. These types of strategies have previously proven effective (see, e.g., Huang,  Nature,  537: 320-327, 2016; Khoury,  Trends Biotechnol,  32: 99-109, 2014; Packer,  Nature Rev Genetics,  16: 379-394, 2015; Privett,  PNAS  USA, 109: 3790-3795, 2012). 
     To improve substrate specificity of Ptb-Buk towards a specific acyl-CoA substrate, Ptb-Buk variants from public databases or generated Ptb-Buk mutants (for example, from directed evolution) can be screened using a high throughput assay, namely overexpressing Ptb-Buk enzyme pairs in  E. coli , adding a test substrate, and screening for ATP production with a bioluminescence assay. The assay can use the well-established practice of correlating ATP concentration with firefly luciferase enzyme bioluminescence. The amenability of this assay to multi-well plate formats would facilitate efficient screening of substrate preference across new Ptb-Buk combinations ( FIG. 33 ). 
     By screening for ATP production rather than depletion of substrate or accumulation of product, the assay avoids measuring spontaneous hydrolysis of the CoA group. However, an alternative approach described in literature, is to use free CoA can be measured using the established assay using Ellman&#39;s reagent (5,5′-dithiobis-(2-nitrobenzoic acid) or DTNB) (Thompson, Appl Environ Microbiol, 56: 607-613, 1990.) in order to estimate the coupling efficiency of the Ptb-Buk reactions ( FIG. 33 ). Acyl-CoAs and corresponding free acids and phospho-intermediates can also be measured during the validation phase using LC-MS/MS. 
     In a high-throughput screening approach, it is difficult gather kinetic data due to the labor involved in protein quantification. Instead, for each preparation of  E. coli  lysate containing Ptb-Buk enzymes, the activity against each substrate of interest (measured as luminescence per unit time) can be compared to the activity against the positive control substrate (butyryl-CoA) and against acetyl-CoA (the physiological substrate that will likely provide the greatest competition for enzyme active sites against target acyl-CoA). 
     In order to ensure that the assay is not biased due to native phosphotransacetylase (Pta) and/or acetate kinase (Ack) activity, the assay can also be evaluated in an  E. coli  strain where pta and/or ack genes have been knocked out. 
     Production of Acetone and Isopropanol 
     Acetone and isopropanol are important industrial solvents with a combined market size of 8 million tons and a global market value of $8.5-11 billion. In addition, acetone and isopropanol are precursors to valuable downstream products, including polymethyl methacrylate (PMMA), which has a global market value of $7 billion, isobutylene, which has a global market value of $25-29 billion, and propylene, which has a global market value of $125 billion. Additionally, a route from acetone to jet fuel has recently been reported. Currently, industrial acetone production is directly linked to petrochemical phenol production, as it is a by-product of the cumene process. Around 92% of acetone output by volume is a co-product of phenol production from cumene. This has significant implications on both environment and market. In the cumene process, per mol phenol produced one mol of sodium sulfite accumulates posing a serious waste management problem and a challenge to natural environments and human health. The world market demand for phenol is expected to stagnate or decline, while the demand for acetone is predicted to rise. Alternative phenol production routes from direct oxidation of benzene are in development and expected to commercialize soon; this could result in a complete elimination of acetone production. 
     Acetone has been produced at industrial scale for almost 100 years, as a by-product of butanol in ABE fermentation. While industrial ABE fermentation declined in the second half of the 20 th  century due to low oil prices and high sugar costs, it has recently revived, with several commercial plants built during the last few years. Multiple groups have also demonstrated acetone production from sugar in heterologous hosts that express the corresponding enzymes from ABE fermentation organisms, in particular  E. coli  and yeast through metabolic engineering and synthetic biology approaches by several academic groups. However, low yields and high costs associated the pre-treatment needed to release the polysaccharide-component of biomass make the production of acetone via standard fermentation uneconomic as current biochemical conversion technologies do not utilize the lignin component of biomass, which can constitute up to 40% of this material. 
     The invention provides a microorganism capable of producing acetone or precursors thereof from a substrate. The invention further provides a method of producing acetone or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of acetone may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     Acetone via steps 1, 2, and 3: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, and 3, whereby the microorganism is capable of producing acetone or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, and 3 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary:secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), the microorganism may be modified to knock down or knock out the expression of primary:secondary alcohol dehydrogenase (e.g., by disrupting the gene encoding the primary:secondary alcohol dehydrogenase), such that the microorganism produces acetone without converting it to isopropanol (WO 2015/085015). 
     Acetone via steps 1, 13, 14, 15, and 3: In one embodiment, the invention provides a microorganism comprising exogenous enzymes for steps 1, 13, 14, 15, and 3, whereby the microorganism is capable of producing acetone or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 14 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 14, 15, and 3 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary:secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), the microorganism may be modified to knock down or knock out the expression of primary: secondary alcohol dehydrogenase (e.g., by disrupting the gene encoding the primary:secondary alcohol dehydrogenase), such that the microorganism produces acetone without converting it to isopropanol (WO 2015/085015). 
     In one embodiment, the microorganism may comprise more than one pathway for the production of acetone. 
     The invention provides a microorganism capable of producing isopropanol or precursors thereof from a substrate. The invention further provides a method of producing isopropanol or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of isopropanol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     Isopropanol via steps 1, 2, 3, and 4: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, 3, and 4, whereby the microorganism is capable of producing isopropanol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, 3, and 4 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary:secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), introduction of an exogenous enzyme for step 4 is not required to produce isopropanol. However, modification of the microorganism, for example, to overexpress a native primary:secondary alcohol dehydrogenase may result in enhanced production of isopropanol. 
     Isopropanol via steps 1, 13, 14, 15, 3, and 4: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 14, 15, 3, and 4, whereby the microorganism is capable of producing isopropanol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 14 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 14, 15, 3, and 4 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary:secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), introduction of an exogenous enzyme for step 4 is not required to produce isopropanol. However, modification of the microorganism, for example, to overexpress a native primary:secondary alcohol dehydrogenase may result in enhanced production of isopropanol. 
     In one embodiment, the microorganism may comprise more than one pathway for the production of isopropanol. 
     Production of Isobutylene 
     Isobutylene is a major chemical building block with a market size of over 15 million tons and a global market value of $25-29 billion. Beyond its use in chemistry and as a fuel additive (15 Mt/yr), isobutylene may be converted to isooctane, a high performance, drop-in fuel for gasoline cars. Global Bioenergies has filed patent applications on the fermentative production of isobutene (i.e., isobutylene) from acetone, but none of the disclosed routes involve Ptb-Buk (WO 2010/001078; EP 2295593; WO 2011/076691; van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012). 
     The invention provides a microorganism capable of producing isobutylene or precursors thereof from a substrate. The invention further provides a method of producing isobutylene or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of isobutylene may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
       FIG. 1  shows two alternative routes to isobutylene. The first involves the production of isobutylene via steps 1, 2, 3, 5, and 6. The second involves the production of isobutylene via steps 1, 2, 3, 7, 8, and 6. Steps 2 and 8 may be catalyzed by Ptb-Buk. Accordingly, each route may involve Ptb-Buk. 
     Isobutylene via steps 1, 2, 3, 5, and 6: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, 3, 5, and 6, whereby the microorganism is capable of producing isobutylene or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, 3, 5, and 6 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary: secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), the microorganism may be modified to knock down or knock out the expression of primary:secondary alcohol dehydrogenase (e.g., by disrupting the gene encoding the primary:secondary alcohol dehydrogenase) to prevent the conversion of acetone to isopropanol and maximize the conversion of acetone to isobutylene. 
     Isobutylene via steps 1, 2, 3, 7, 8, and 6: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, 3, 7, 8, and 6, whereby the microorganism is capable of producing isobutylene or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 and/or step 8 are catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, 3, 7, 8, and 6 are described elsewhere in this application. If the microorganism is derived from a parental microorganism that natively contains a primary:secondary alcohol dehydrogenase capable of converting acetone to isopropanol (step 4) (e.g.,  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei ), the microorganism may be modified to knock down or knock out the expression of primary: secondary alcohol dehydrogenase (e.g., by disrupting the gene encoding the primary:secondary alcohol dehydrogenase) to prevent the conversion of acetone to isopropanol and maximize the conversion of acetone to isobutylene. 
     Production of 3-Hydroxybutyrate 
     3-Hydroxybutyrate (3-HB) is a four carbon carboxylic acid in the family of betahydroxy acids. 3-hydroxybutyrate is a cosmetic ingredient for oily skin clarification, an intermediate for anti-aging cream formulations, an intermediate for polyhydroxybutyrate (PHB), a biodegradable polymer resin, and co-monomer with other polyhydroxy acids for novel bioplastics. Additionally, 3-hydroxybutyrate has specialty applications in biocompatible and biodegradable nanocomposites, particularly for medical implants, intermediate for C3/C4 chemicals, chiral building blocks, and fine chemicals. Although the production of (R)- and (S)-3-hydroxybutyrate by recombinant  E. coli  grown on glucose, the production of 3-hydroxybutyrate has not been demonstrated from microorganisms grown on gaseous substrates (Tseng,  Appl Environ Microbiol,  75: 3137-3145, 2009). Notably, the system previously demonstrated in  E. coli  was not directly transferrable to acetogens, including  C. autoethanogenum , due to the presence of native thioesterases in acetogens. Although  E. coli  also has a thioesterase TesB that can act on 3-HB-CoA, Tseng showed that background activity is minimal (&lt;0.1 g/L). While in  E. coli  production of stereopure isomers were reported, the inventors surprisingly found that a mix of isomers were produced in  C. autoethanogenum . Without being bound to this theory, this is likely a result of native isomerase activity. This enables the combination of an (S)-specific 3-hydroxybutyryl-CoA dehydrogenase (Hbd) to be combined with the (R)-specific Ptb-Buk for optimized production. To produce stereopure isomers, this activity can be knocked-out. Taken together, it this invention enables to produce several g/L of 3-HB compared to low production in  E. coli  and using Ptb-Buk any combination of (R)- or (S)-specific 3-hydroxybutyryl-CoA dehydrogenase and native  Clostridium autoethanogenum  thioesterase. 
     The invention provides a microorganism capable of producing 3-hydroxybutyrate or precursors thereof from a substrate. The invention further provides a method of producing 3-hydroxybutyrate or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 3-hydroxybutyrate may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
       FIG. 1  shows two alternative routes to 3-hydroxybutyrate. The first involves the production of 3-hydroxybutyrate via steps 1, 2, and 15. The second involves the production of 3-hydroxybutyrate via steps 1, 13, and 14. Steps 2 and 14 may be catalyzed by Ptb-Buk. Accordingly, each route may involve Ptb-Buk. In one embodiment, the microorganism may comprise more than one pathway for the production of 3-hydroxybutyrate, wherein Ptb-Buk may catalyze more than one step (e.g., steps 2 and 14). 
     3-Hydroxybutyrate via steps 1, 2, and 15: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, and 15, whereby the microorganism is capable of producing 3-hydroxybutyrate or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, and 15 are described elsewhere in this application. 
     3-Hydroxybutyrate via steps 1, 13, and 14: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, and 14, whereby the microorganism is capable of producing 3-hydroxybutyrate or precursors thereof from substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 14 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, and 14 are described elsewhere in this application. 
     Production of 1,3-Butanediol 
     1,3-Butanediol (1,3-BDO) is commonly used as a solvent for food flavoring agents and is a co-monomer used in certain polyurethane and polyester resins. More importantly, 1,3-butanediol may be catalytically converted to 1,3-butadiene (Makshina,  Chem Soc Rev,  43: 7917-7953, 2014). Butadiene is used to produce rubber, plastics, lubricants, latex, and other products. While much of the butadiene produced today is used for the rubber in automobile tires, it can also be used to produce adiponitrile, which can be used in the manufacture of nylon 6,6. Global demand for butadiene is on the rise. In 2011, there was an estimated 10.5 million tons of demand, valued at $40 billion. 
     The invention provides a microorganism capable of producing 1,3-butanediol or precursors thereof from a substrate. The invention further provides a method of producing 1,3-butanediol or precursors thereof by culturing such a microorganism in the presence of substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 1,3-butanediol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     In certain embodiments, the microorganism may produce 1,3-butanediol without co-production of ethanol (or with production of only a small amount of ethanol, e.g., less than 0.1-1.0 g/L ethanol or less than 1-10 g/L ethanol). 
       FIG. 1  shows three alternative routes to 1,3-butanediol. The first involves the production of 1,3-butanediol via steps 1, 2, 15, 16, and 17. The second involves the production of 1,3-butanediol via steps 1, 13, 14, 16, and 17. The third involves the production of 1,3-butanediol via steps 1, 13, 18, and 17. Steps 2 and 14 may be catalyzed by Ptb-Buk. Accordingly, at least the first and second routes may involve Ptb-Buk. In one embodiment, the microorganism may comprise more than one pathway for the production of 1,3-butanediol. In a related embodiment, the Ptb-Buk may catalyze more than one step (e.g., steps 2 and 14). 
     1,3-Butanediol via steps 1, 2, 15, 16, and 17: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 2, 15, 16, and 17, whereby the microorganism is capable of producing 1,3-butanediol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 2 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 2, 15, 16, and 17 are described elsewhere in this application. 
     1,3-Butanediol via steps 1, 13, 14, 16, and 17: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 14, 16, and 17, whereby the microorganism is capable of producing 1,3-butanediol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 14 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 14, 16, and 17 are described elsewhere in this application. 
     1,3-Butanediol via steps 1, 13, 18, and 17: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 18, and 17, whereby the microorganism is capable of producing 1,3-butanediol or precursors thereof from a substrate, such as a gaseous substrate ( FIG. 11 ). Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. Exemplary types and sources of enzymes for steps 1, 13, 18, and 17 are described elsewhere in this application. A similar route has been demonstrated in  E. coli , but not in acetogens such as  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  (Kataoka,  J Biosci Bioeng,  115: 475-480, 2013). Although the use of Ptb-Buk results in the production of (R)-1,3-butanediol, this route, which does not require the use of Ptb-Buk, may result in the production of (5)-1,3-butanediol. 
     Production of 2-Hydroxyisobutyrate 
     2-Hydroxyisobutyrate (2-HIB) is a four carbon carboxylic acid that may serve as a building block for many types of polymers. The methyl ester of methacrylic acid, which can be synthesized by dehydration of 2-hydroxyisobutyrate or via the corresponding amide, is polymerized to polymethylmethacrylate (PMMA) for the production of acrylic glass, durable coatings, and inks. For this compound alone, the global market exceeds 3 million tons. Other branched C4 carboxylic acids, e.g., chloro- and amino-derivatives of 2-hydroxyisobutyrate, as well as isobutylene glycol and its oxide, are also used in polymers and for many other applications. 
     The stereospecificity of the Ptb-Buk system is particularly useful in overcoming the limitations of the current state of art with respect to the production of 2-hydroxyisobutyrate. Both Ptb-Buk and thioesterases are promiscuous, such that side activity with 3-hydroxybutyryl-CoA may divert resources away from target pathways for the production of 2-hydroxyisobutyryl-CoA (see, e.g.,  FIG. 1  and  FIG. 8 ). However, Ptb-Buk is able to distinguish between stereoisomers and will act on (R)-3-hydroxybutyryl-CoA, but not on (S)-3-hydroxybutyryl-CoA. In contrast, thioesterases are not able to distinguish between 3-hydroxybutyryl-CoA stereoisomers. In a preferred embodiment, an (S)-specific acetoacetyl-CoA hydratase (EC 4.2.1.119) (step 13) is chosen in combination with the Ptb-Buk (step 20) to avoid losses to 3-hydroxybutyrate and maximize 2-hydroxyisobutyrate yield ( FIG. 8 ). The (S)-specific form of 3-hydroxybutyryl-CoA is also the preferred substrate for the 2-hydroxyisobutyryl-CoA mutase (EC 5.4.99.-) (step 19) (Yaneva,  J Biol Chem,  287: 15502-15511, 2012). 
     The invention provides a microorganism capable of producing 2-hydroxyisobutyrate or precursors thereof from a substrate. The invention further provides a method of producing 2-hydroxyisobutyrate or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 2-hydroxyisobutyrate may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     2-Hydroxyisobutyrate via steps 1, 13, 19, and 20: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 19, and 20, whereby the microorganism is capable of producing 2-hydroxyisobutyrate or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 20 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 19, and 20 are described elsewhere in this application. 
     In certain embodiments, the invention also provides a microorganism capable of producing 2-hydroxybutyrate (2-HB) or precursors thereof from a substrate. The invention further provides a method of producing 2-hydroxybutyrate or precursors thereof by culturing such a microorganism in the presence of a substrate. Without wishing to be bound by any particular theory, the inventors believe the observed production of 2-hydroxybutyrate is attributable to nonspecific mutase activity in microorganisms such as  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei.    
     Production of Adipic Acid 
     Adipic acid is the most important dicarboxylic acid with an estimated market of greater US $4.5 billion with about 2.5 billion kgs produced annually. Over 60% of produced adipic acid is being used as monomer precursor for the production of nylon and the global market for adipic acid is expected to reach US $7.5 billion by 2019. Currently, adipic acid is almost excusively produced petrochemically, e.g. by carbonylation of butadiene. 
     The invention provides a microorganism capable of producing adipic acid or precursors thereof from a substrate ( FIG. 34 ). The invention further provides a method of producing adipic acid or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of adipic acid may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     Adipic acid via steps 22, 23, 24, 25, and 26: In one embodiment, the invention provides a microorganism comprising enzymes for steps 22, 23, 24, 25, and 26, whereby the microorganism is capable of producing adipic acid or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 26 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 22, 23, 24, 25, and 26 are described elsewhere in this application. 
     Adipic acid via steps 21, 22, 23, 24, 25, and 26: In one embodiment, the invention provides a microorganism comprising enzymes for steps 21, 22, 23, 24, 25, and 26, whereby the microorganism is capable of producing adipic acid or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 26 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 21, 22, 23, 24, 25, and 26 are described elsewhere in this application. 
     In one embodiment, the microorganism may comprise more than one pathway for the production of adipic acid. 
     Production of 1,3-Hexanediol 
     The invention provides a microorganism capable of producing 1,3-hexanediol or precursors thereof from a substrate ( FIG. 35 ). The invention further provides a method of producing 1,3-hexanediol or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 1,3-hexanediol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     The pathways depicted in  FIG. 35  begin with 3-hydroxybutyryl-CoA, which may be produced via steps 1 and 13, as depicted in  FIG. 1 . 
     1,3-Hexanediol via steps 1, 13, 27, 31, 32, 36, 37, 38, and 39: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 27, 31, 32, 36, 37, 38, and 39, whereby the microorganism is capable of producing 1,3-hexanediol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 37 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 27, 31, 32, 36, 37, 38, and 39 are described elsewhere in this application. 
     Production of 3-Methyl-2-butanol 
     The invention provides a microorganism capable of producing 3-methyl-2-butanol or precursors thereof from a substrate ( FIG. 35 ). The invention further provides a method of producing 3-methyl-2-butanol or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 3-methyl-2-butanol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     The pathways depicted in  FIG. 35  begin with 3-hydroxybutyryl-CoA, which may be produced via steps 1 and 13, as depicted in  FIG. 1 . 
     3-Methyl-2-butanol via steps 1, 13, 27, 31, 32, 33, 34, and 35: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 27, 31, 32, 33, 34, and 35, whereby the microorganism is capable of producing 3-methyl-2-butanol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 33 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 27, 31, 32, 33, 34, and 35 are described elsewhere in this application. 
     Production of 2-Buten-1-ol 
     The invention provides a microorganism capable of producing 2-buten-1-ol or precursors thereof from a substrate ( FIG. 35 ). The invention further provides a method of producing 2-buten-1-ol or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of 2-buten-1-ol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     The pathways depicted in  FIG. 35  begin with 3-hydroxybutyryl-CoA, which may be produced via steps 1 and 13, as depicted in  FIG. 1 . 
     2-Buten-1-ol via steps 1, 13, 27, 28, 29, and 30: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 13, 27, 28, 29, and 30, whereby the microorganism is capable of producing 2-buten-1-ol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 28 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 13, 27, 28, 29, and 30 are described elsewhere in this application. 
     Production of Isovalerate 
     The invention provides a microorganism capable of producing isovalerate or precursors thereof from a substrate ( FIG. 36 ). The invention further provides a method of producing isovalerate or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of isovalerate may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     Isovalerate via steps 1, 40, 41, 42, 43, and 44: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 40, 41, 42, 43, and 44, whereby the microorganism is capable of producing isovalerate or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 44 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 40, 41, 42, 43, and 44 are described elsewhere in this application. 
     Production of Isoamyl Alcohol 
     The invention provides a microorganism capable of producing isoamyl alcohol or precursors thereof from a substrate ( FIG. 36 ). The invention further provides a method of producing isoamyl alcohol or precursors thereof by culturing such a microorganism in the presence of a substrate. In preferred embodiments, the microorganism is derived from a parental microorganism selected from the group consisting of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . However, the microorganism may also be derived from an entirely different microorganism, e.g.,  Eschericia coli . The enzymatic pathways described for the production of isoamyl alcohol may comprise endogenous enzymes and, where endogenous enzyme activity is absent or low, exogenous enzymes. 
     Isoamyl alcohol via steps 1, 40, 41, 42, 43, 44, 45, and 46: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 40, 41, 42, 43, 44, 45, and 46, whereby the microorganism is capable of producing isoamyl alcohol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. In a preferred embodiment, step 44 is catalyzed by Ptb-Buk. Exemplary types and sources of enzymes for steps 1, 40, 41, 42, 43, 44, 45, and 46 are described elsewhere in this application. 
     Isoamyl alcohol via steps 1, 40, 41, 42, 43, 47 and 46: In one embodiment, the invention provides a microorganism comprising enzymes for steps 1, 40, 41, 42, 43, 47 and 46, whereby the microorganism is capable of producing isoamyl alcohol or precursors thereof from a substrate, such as a gaseous substrate. Typically, at least one of the enzymes in this pathway is exogenous to the microorganism. Exemplary types and sources of enzymes for steps 1, 40, 41, 42, 43, 47 and 46 are described elsewhere in this application. 
     In one embodiment, the microorganism may comprise more than one pathway for the production of isoamyl alcohol. 
     Production of Additional Products 
     The invention provides a microorganism comprising exogenous Ptb-Buk and exogenous or endogenous aldehyde:ferredoxin oxidoreductase (AOR). Such a microorganism may produce, for example, 1-propanol, 1-butanol, 1-hexanol, and 1-octanol or precursors thereof from acetyl-CoA generated, for example, from a gaseous substrate ( FIG. 32 ). The invention further provides a method of producing 1-propanol, 1-butanol, 1-hexanol, and 1-octanol or precursors thereof by culturing such a microorganism in the presence of a gaseous substrate.  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei  natively comprise AOR. However, AOR may be overexpressed in such microorganisms in combination with expression of exogenous Ptb-Buk. Alternatively, exogenous AOR and exogenous Ptb-Buk may be expressed in a microorganism other than  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei , such as  Escherichia coli.    
     Production of Precursors and Intermediates 
     The pathways depicted in  FIGS. 1, 34, 35, and 36  may be modified to produce precursors or intermediates of the aforementioned products. In particular, partial enzymatic pathways for any of the pathways described herein may be inserted in a host microorganism to obtain production of precursors or intermediates. 
     Definitions and Background 
     The term “genetic modification” or “genetic engineering” broadly refers to manipulation of the genome or nucleic acids of a microorganism. Likewise, the term “genetically engineered” refers to a microorganism comprising a manipulated genome or nucleic acids. Methods of genetic modification of include, for example, heterologous gene expression, gene or promoter insertion or deletion, nucleic acid mutation, altered gene expression or inactivation, enzyme engineering, directed evolution, knowledge-based design, random mutagenesis methods, gene shuffling, and codon optimization. 
     “Recombinant” indicates that a nucleic acid, protein, or microorganism is the product of genetic modification, engineering, or recombination. Generally, the term “recombinant” refers to a nucleic acid, protein, or microorganism that contains or is encoded by genetic material derived from multiple sources, such as two or more different strains or species of microorganisms. As used herein, the term “recombinant” may also be used to describe a microorganism that comprises a mutated nucleic acid or protein, including a mutated form of an endogenous nucleic acid or protein. 
     “Endogenous” refers to a nucleic acid or protein that is present or expressed in the wild-type or parental microorganism from which the microorganism of the invention is derived. For example, an endogenous gene is a gene that is natively present in the wild-type or parental microorganism from which the microorganism of the invention is derived. In one embodiment, the expression of an endogenous gene may be controlled by an exogenous regulatory element, such as an exogenous promoter. 
     “Exogenous” refers to a nucleic acid or protein that is not present in the wild-type or parental microorganism from which the microorganism of the invention is derived. In one embodiment, an exogenous gene or enzyme may be derived from a heterologous (i.e., different) strain or species and introduced to or expressed in the microorganism of the invention. In another embodiment, an exogenous gene or enzyme may be artificially or recombinantly created and introduced to or expressed in the microorganism of the invention. Exogenous nucleic acids may be adapted to integrate into the genome of the microorganism of the invention or to remain in an extra-chromosomal state in the microorganism of the invention, for example, in a plasmid. 
     “Enzyme activity,” or simply “activity,” refers broadly to enzymatic activity, including, but not limited, to the activity of an enzyme, the amount of an enzyme, or the availability of an enzyme to catalyze a reaction. Accordingly, “increasing” enzyme activity includes increasing the activity of an enzyme, increasing the amount of an enzyme, or increasing the availability of an enzyme to catalyze a reaction. Similarly, “decreasing” enzyme activity includes decreasing the activity of an enzyme, decreasing the amount of an enzyme, or decreasing the availability of an enzyme to catalyze a reaction. 
     With respect to enzyme activity, a “substrate” is a molecule upon which an enzyme acts and a “product” is a molecule produced by the action of an enzyme. A “native substrate,” therefore, is a molecule upon which an enzyme natively acts in a wild-type microorganism and a “native product” is a molecule natively produced by the action of the enzyme in the wild-type microorganism. For example, butanoyl-CoA is the native substrate of Ptb and butanoyl phosphate and is the native substrate of Buk. Additionally, butanoyl phosphate is the native product of Ptb and butyrate (butanoate) is the native product of Buk. Likewise, a “non-native substrate” is a molecule upon which an enzyme does not natively act in a wild-type microorganism and a “non-native product” is a molecule not natively produced by the action of the enzyme in the wild-type microorganism. An enzyme that is capable of acting on multiple different substrates, whether native or non-native, is typically referred to as a “promiscuous” enzyme. The inventors have discovered that Ptb is promiscuous and is capable of accepting a variety of acyl-CoAs and enoyl-CoAs as substrates, such that Ptb-Buk may be used to convert a number of acyl-CoAs and enoyl-CoAs to their corresponding acids or alkenates, respectively, while simultaneously generating ATP. Thus, in preferred embodiments, the Ptb-Buk of the invention acts on non-native substrates (i.e., substrates other than butanoyl-CoA and/or butanoyl phosphate) to produce non-native products (i.e., products other than butanoyl phosphate and/or butyrate (butanoate)). 
     The term “butyryl-CoA” may be used interchangeably herein with “butanoyl-CoA.” 
     The term “energy-generating” or the like may be used interchangeably herein with “energy-conserving” or the like. Both of these terms are commonly used in the literature. 
     “Mutated” refers to a nucleic acid or protein that has been modified in the microorganism of the invention compared to the wild-type or parental microorganism from which the microorganism of the invention is derived. In one embodiment, the mutation may be a deletion, insertion, or substitution in a gene encoding an enzyme. In another embodiment, the mutation may be a deletion, insertion, or substitution of one or more amino acids in an enzyme. 
     In particular, a “disruptive mutation” is a mutation that reduces or eliminates (i.e., “disrupts”) the expression or activity of a gene or enzyme. The disruptive mutation may partially inactivate, fully inactivate, or delete the gene or enzyme. The disruptive mutation may be a knockout (KO) mutation. The disruptive mutation may be any mutation that reduces, prevents, or blocks the biosynthesis of a product produced by an enzyme. The disruptive mutation may include, for example, a mutation in a gene encoding an enzyme, a mutation in a genetic regulatory element involved in the expression of a gene encoding an enzyme, the introduction of a nucleic acid which produces a protein that reduces or inhibits the activity of an enzyme, or the introduction of a nucleic acid (e.g., antisense RNA, siRNA, CRISPR) or protein which inhibits the expression of an enzyme. The disruptive mutation may be introduced using any method known in the art. 
     Introduction of a disruptive mutation results in a microorganism of the invention that produces no target product or substantially no target product or a reduced amount of target product compared to the parental microorganism from which the microorganism of the invention is derived. For example, the microorganism of the invention may produce no target product or at least about 1%, 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% less target product than the parental microorganism. For example, the microorganism of the invention may produce less than about 0.001, 0.01, 0.10, 0.30, 0.50, or 1.0 g/L target product. 
     “Codon optimization” refers to the mutation of a nucleic acid, such as a gene, for optimized or improved translation of the nucleic acid in a particular strain or species. Codon optimization may result in faster translation rates or higher translation accuracy. In a preferred embodiment, the genes of the invention are codon optimized for expression in  Clostridium , particularly  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . In a further preferred embodiment, the genes of the invention are codon optimized for expression in  Clostridium autoethanogenum  LZ1561, which is deposited under DSMZ accession number DSM23693. 
     “Overexpressed” refers to an increase in expression of a nucleic acid or protein in the microorganism of the invention compared to the wild-type or parental microorganism from which the microorganism of the invention is derived. Overexpression may be achieved by any means known in the art, including modifying gene copy number, gene transcription rate, gene translation rate, or enzyme degradation rate. 
     The term “variants” includes nucleic acids and proteins whose sequence varies from the sequence of a reference nucleic acid and protein, such as a sequence of a reference nucleic acid and protein disclosed in the prior art or exemplified herein. The invention may be practiced using variant nucleic acids or proteins that perform substantially the same function as the reference nucleic acid or protein. For example, a variant protein may perform substantially the same function or catalyze substantially the same reaction as a reference protein. A variant gene may encode the same or substantially the same protein as a reference gene. A variant promoter may have substantially the same ability to promote the expression of one or more genes as a reference promoter. 
     Such nucleic acids or proteins may be referred to herein as “functionally equivalent variants.” By way of example, functionally equivalent variants of a nucleic acid may include allelic variants, fragments of a gene, mutated genes, polymorphisms, and the like. Homologous genes from other microorganisms are also examples of functionally equivalent variants. These include homologous genes in species such as  Clostridium acetobutylicum, Clostridium beijerinckii , or  Clostridium ljungdahlii , the details of which are publicly available on websites such as Genbank or NCBI. Functionally equivalent variants also include nucleic acids whose sequence varies as a result of codon optimization for a particular microorganism. A functionally equivalent variant of a nucleic acid will preferably have at least approximately 70%, approximately 80%, approximately 85%, approximately 90%, approximately 95%, approximately 98%, or greater nucleic acid sequence identity (percent homology) with the referenced nucleic acid. A functionally equivalent variant of a protein will preferably have at least approximately 70%, approximately 80%, approximately 85%, approximately 90%, approximately 95%, approximately 98%, or greater amino acid identity (percent homology) with the referenced protein. The functional equivalence of a variant nucleic acid or protein may be evaluated using any method known in the art. 
     Nucleic acids may be delivered to a microorganism of the invention using any method known in the art. For example, nucleic acids may be delivered as naked nucleic acids or may be formulated with one or more agents, such as liposomes. The nucleic acids may be DNA, RNA, cDNA, or combinations thereof, as is appropriate. Restriction inhibitors may be used in certain embodiments. Additional vectors may include plasmids, viruses, bacteriophages, cosmids, and artificial chromosomes. In a preferred embodiment, nucleic acids are delivered to the microorganism of the invention using a plasmid. By way of example, transformation (including transduction or transfection) may be achieved by electroporation, ultrasonication, polyethylene glycol-mediated transformation, chemical or natural competence, protoplast transformation, prophage induction, or conjugation. In certain embodiments having active restriction enzyme systems, it may be necessary to methylate a nucleic acid before introduction of the nucleic acid into a microorganism. 
     Furthermore, nucleic acids may be designed to comprise a regulatory element, such as a promoter, to increase or otherwise control expression of a particular nucleic acid. The promoter may be a constitutive promoter or an inducible promoter. Ideally, the promoter is a Wood-Ljungdahl pathway promoter, a ferredoxin promoter, a pyruvate:ferredoxin oxidoreductase promoter, an Rnf complex operon promoter, an ATP synthase operon promoter, or a phosphotransacetylase/acetate kinase operon promoter. 
     A “microorganism” is a microscopic organism, especially a bacterium, archaeon, virus, or fungus. The microorganism of the invention is typically a bacterium. As used herein, recitation of “microorganism” should be taken to encompass “bacterium.” 
     A “parental microorganism” is a microorganism used to generate a microorganism of the invention. The parental microorganism may be a naturally-occurring microorganism (i.e., a wild-type microorganism) or a microorganism that has been previously modified (i.e., a mutant or recombinant microorganism). The microorganism of the invention may be modified to express or overexpress one or more enzymes that were not expressed or overexpressed in the parental microorganism. Similarly, the microorganism of the invention may be modified to contain one or more genes that were not contained by the parental microorganism. The microorganism of the invention may also be modified to not express or to express lower amounts of one or more enzymes that were expressed in the parental microorganism. In one embodiment, the parental microorganism is  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . In a preferred embodiment, the parental microorganism is  Clostridium autoethanogenum  LZ1561, which is deposited under DSMZ accession number DSM23693. 
     The term “derived from” indicates that a nucleic acid, protein, or microorganism is modified or adapted from a different (e.g., a parental or wild-type) nucleic acid, protein, or microorganism, so as to produce a new nucleic acid, protein, or microorganism. Such modifications or adaptations typically include insertion, deletion, mutation, or substitution of nucleic acids or genes. Generally, the microorganism of the invention is derived from a parental microorganism. In one embodiment, the microorganism of the invention is derived from  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . In a preferred embodiment, the microorganism of the invention is derived from  Clostridium autoethanogenum  LZ1561, which is deposited under DSMZ accession number DSM23693. 
     The microorganism of the invention may be further classified based on functional characteristics. For example, the microorganism of the invention may be or may be derived from a C1-fixing microorganism, an anaerobe, an acetogen, an ethanologen, a carboxydotroph, and/or a methanotroph. Table 1 provides a representative list of microorganisms and identifies their functional characteristics. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 C1-fixing 
                 Anaerobe 
                 Acetogen 
                 Ethanologen 
                 Autotroph 
                 Carboxydotroph 
                 Methanotroph 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 
                   Acetobacterium woodii 
                 
                 + 
                 + 
                 + 
                 +/− 1   
                 − 
                 − 
                 − 
               
               
                 
                   Alkalibaculum bacchii 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Blautia producta 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Butyribacterium methylotrophicum 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium aceticum 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium autoethanogenum 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium carboxidivorans 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium coskatii 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium drakei 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium formicoaceticum 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium ljungdahlii 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium magnum 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 +/− 2   
                 − 
               
               
                 
                   Clostridium ragsdalei 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium scatologenes 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Eubacterium limosum 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Moorella thermautotrophica 
                 
                 + 
                 + 
                 + 
                 + 
                 + 
                 + 
                 − 
               
               
                   Moorella thermoacetica  (formerly 
                 + 
                 + 
                 + 
                 − 3   
                 + 
                 + 
                 − 
               
               
                 
                   Clostridium thermoaceticum) 
                 
               
               
                 
                   Oxobacter pfennigii 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 + 
                 − 
               
               
                 
                   Sporomusa ovata 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 +/− 4   
                 − 
               
               
                 
                   Sporomusa silvacetica 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 +/− 5   
                 − 
               
               
                 
                   Sporomusa sphaeroides 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 +/− 6   
                 − 
               
               
                 
                   Thermoanaerobacter kiuvi 
                 
                 + 
                 + 
                 + 
                 − 
                 + 
                 − 
                 − 
               
               
                   
               
               
                   1   Acetobacterium woodi  can produce ethanol from fructose, but not from gas. 
               
               
                   2 It has not been investigated whether  Clostridium magnum  can grow on CO. 
               
               
                   3 One strain of  Moorella thermoacetica ,  Moorella  sp. HUC22-1, has been reported to produce ethanol from gas. 
               
               
                   4 It has not been investigated whether  Sporomusa ovata  can grow on CO. 
               
               
                   5 It has not been investigated whether  Sporomusa silvacetica  can grow on CO. 
               
               
                   6 It has not been investigated whether  Sporomusa sphaeroides  can grow on CO. 
               
            
           
         
       
     
     “C1” refers to a one-carbon molecule, for example, CO, CO 2 , CH 4 , or CH 3 OH. “C1-oxygenate” refers to a one-carbon molecule that also comprises at least one oxygen atom, for example, CO, CO 2 , or CH 3 OH. “C1-carbon source” refers a one carbon-molecule that serves as a partial or sole carbon source for the microorganism of the invention. For example, a C1-carbon source may comprise one or more of CO, CO 2 , CH 4 , CH 3 OH, or CH 2 O 2 . Preferably, the C1-carbon source comprises one or both of CO and CO 2 . A “C1-fixing microorganism” is a microorganism that has the ability to produce one or more products from a C1-carbon source. Typically, the microorganism of the invention is a C1-fixing bacterium. In a preferred embodiment, the microorganism of the invention is derived from a C1-fixing microorganism identified in Table 1. 
     An “anaerobe” is a microorganism that does not require oxygen for growth. An anaerobe may react negatively or even die if oxygen is present above a certain threshold. Typically, the microorganism of the invention is an anaerobe. In a preferred embodiment, the microorganism of the invention is derived from an anaerobe identified in Table 1. 
     An “acetogen” is a microorganism that produces or is capable of producing acetate (or acetic acid) as a product of anaerobic respiration. Typically, acetogens are obligately anaerobic bacteria that use the Wood-Ljungdahl pathway as their main mechanism for energy conservation and for synthesis of acetyl-CoA and acetyl-CoA-derived products, such as acetate (Ragsdale,  Biochim Biophys Acta,  1784: 1873-1898, 2008). Acetogens use the acetyl-CoA pathway as a (1) mechanism for the reductive synthesis of acetyl-CoA from CO 2 , (2) terminal electron-accepting, energy conserving process, (3) mechanism for the fixation (assimilation) of CO 2  in the synthesis of cell carbon (Drake, Acetogenic Prokaryotes, In: The Prokaryotes, 3 rd  edition, p. 354, New York, N.Y., 2006). All naturally occurring acetogens are C1-fixing, anaerobic, autotrophic, and non-methanotrophic. Typically, the microorganism of the invention is an acetogen. In a preferred embodiment, the microorganism of the invention is derived from an acetogen identified in Table 1. 
     An “ethanologen” is a microorganism that produces or is capable of producing ethanol. Typically, the microorganism of the invention is an ethanologen. In a preferred embodiment, the microorganism of the invention is derived from an ethanologen identified in Table 1. 
     An “autotroph” is a microorganism capable of growing in the absence of organic carbon. Instead, autotrophs use inorganic carbon sources, such as CO and/or CO 2 . Typically, the microorganism of the invention is an autotroph. In a preferred embodiment, the microorganism of the invention is derived from an autotroph identified in Table 1. 
     A “carboxydotroph” is a microorganism capable of utilizing CO as a sole source of carbon. Typically, the microorganism of the invention is a carboxydotroph. In a preferred embodiment, the microorganism of the invention is derived from a carboxydotroph identified in Table 1. 
     A “methanotroph” is a microorganism capable of utilizing methane as a sole source of carbon and energy. In certain embodiments, the microorganism of the invention is derived from a methanotroph. 
     More broadly, the microorganism of the invention may be derived from any genus or species identified in Table 1. 
     In a preferred embodiment, the microorganism of the invention is derived from the cluster of  Clostridia  comprising the species  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei . These species were first reported and characterized by Abrini,  Arch Microbiol,  161: 345-351, 1994 ( Clostridium autoethanogenum ), Tanner,  Int J System Bacteriol,  43: 232-236, 1993 ( Clostridium ljungdahlii ), and Huhnke, WO 2008/028055 ( Clostridium ragsdalei ). 
     These three species have many similarities. In particular, these species are all C1-fixing, anaerobic, acetogenic, ethanologenic, and carboxydotrophic members of the genus  Clostridium . These species have similar genotypes and phenotypes and modes of energy conservation and fermentative metabolism. Moreover, these species are clustered in clostridial rRNA homology group I with 16S rRNA DNA that is more than 99% identical, have a DNA G+C content of about 22-30 mol %, are gram-positive, have similar morphology and size (logarithmic growing cells between 0.5-0.7×3-5 μm), are mesophilic (grow optimally at 30-37° C.), have similar pH ranges of about 4-7.5 (with an optimal pH of about 5.5-6), lack cytochromes, and conserve energy via an Rnf complex. Also, reduction of carboxylic acids into their corresponding alcohols has been shown in these species (Perez,  Biotechnol Bioeng,  110:1066-1077, 2012). Importantly, these species also all show strong autotrophic growth on CO-containing gases, produce ethanol and acetate (or acetic acid) as main fermentation products, and produce small amounts of 2,3-butanediol and lactic acid under certain conditions. 
     However, these three species also have a number of differences. These species were isolated from different sources:  Clostridium autoethanogenum  from rabbit gut,  Clostridium ljungdahlii  from chicken yard waste, and  Clostridium ragsdalei  from freshwater sediment. These species differ in utilization of various sugars (e.g., rhamnose, arabinose), acids (e.g., gluconate, citrate), amino acids (e.g., arginine, histidine), and other substrates (e.g., betaine, butanol). Moreover, these species differ in auxotrophy to certain vitamins (e.g., thiamine, biotin). These species have differences in nucleic and amino acid sequences of Wood-Ljungdahl pathway genes and proteins, although the general organization and number of these genes and proteins has been found to be the same in all species (Köpke,  Curr Opin Biotechnol,  22: 320-325, 2011). 
     Thus, in summary, many of the characteristics of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei  are not specific to that species, but are rather general characteristics for this cluster of C1-fixing, anaerobic, acetogenic, ethanologenic, and carboxydotrophic members of the genus  Clostridium . However, since these species are, in fact, distinct, the genetic modification or manipulation of one of these species may not have an identical effect in another of these species. For instance, differences in growth, performance, or product production may be observed. 
     The microorganism of the invention may also be derived from an isolate or mutant of  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . Isolates and mutants of  Clostridium autoethanogenum  include JA1-1 (DSM10061) (Abrini,  Arch Microbiol,  161: 345-351, 1994), LBS1560 (DSM19630) (WO 2009/064200), and LZ1561 (DSM23693). Isolates and mutants of  Clostridium ljungdahlii  include ATCC 49587 (Tanner,  Int J Syst Bacteriol,  43: 232-236, 1993), PETCT (DSM13528, ATCC 55383), ERI-2 (ATCC 55380) (U.S. Pat. No. 5,593,886), C-01 (ATCC 55988) (U.S. Pat. No. 6,368,819), O-52 (ATCC 55989) (U.S. Pat. No. 6,368,819), and OTA-1 (Tirado-Acevedo, Production of bioethanol from synthesis gas using  Clostridium ljungdahlii , PhD thesis, North Carolina State University, 2010). Isolates and mutants of  Clostridium ragsdalei  include PI 1 (ATCC BAA-622, ATCC PTA-7826) (WO 2008/028055). 
     In some embodiments, however, the microorganism of the invention is a microorganism other than  Clostridium autoethanogenum, Clostridium ljungdahlii , or  Clostridium ragsdalei . For example, the microorganism may be selected from the group consisting of  Escherichia coli, Saccharomyces cerevisiae, Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharbutyricum, Clostridium saccharoperbutylacetonicum, Clostridium butyricum, Clostridium diolis, Clostridium kluyveri, Clostridium pasterianium, Clostridium novyi, Clostridium difficile, Clostridium thermocellum, Clostridium cellulolyticum, Clostridium cellulovorans, Clostridium phytofermentans, Lactococcus lactis, Bacillus subtilis, Bacillus licheniformis, Zymomonas mobilis, Klebsiella oxytoca, Klebsiella pneumonia, Corynebacterium glutamicum, Trichoderma reesei, Cupriavidus necator, Pseudomonas putida, Lactobacillus plantarum , and  Methylobacterium extorquens.    
     “Substrate” refers to a carbon and/or energy source for the microorganism of the invention. Typically, the substrate is gaseous and comprises a C1-carbon source, for example, CO, CO 2 , and/or CH 4 . Preferably, the substrate comprises a C1-carbon source of CO or CO+CO 2 . The substrate may further comprise other non-carbon components, such as H 2 , N 2 , or electrons. 
     The substrate generally comprises at least some amount of CO, such as about 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 mol % CO. The substrate may comprise a range of CO, such as about 20-80, 30-70, or 40-60 mol % CO. Preferably, the substrate comprises about 40-70 mol % CO (e.g., steel mill or blast furnace gas), about 20-30 mol % CO (e.g., basic oxygen furnace gas), or about 15-45 mol % CO (e.g., syngas). In some embodiments, the substrate may comprise a relatively low amount of CO, such as about 1-10 or 1-20 mol % CO. The microorganism of the invention typically converts at least a portion of the CO in the substrate to a product. In some embodiments, the substrate comprises no or substantially no CO. 
     The substrate may comprise some amount of H 2 . For example, the substrate may comprise about 1, 2, 5, 10, 15, 20, or 30 mol % H 2 . In some embodiments, the substrate may comprise a relatively high amount of H 2 , such as about 60, 70, 80, or 90 mol % H 2 . In further embodiments, the substrate comprises no or substantially no H 2 . 
     The substrate may comprise some amount of CO 2 . For example, the substrate may comprise about 1-80 or 1-30 mol % CO 2 . In some embodiments, the substrate may comprise less than about 20, 15, 10, or 5 mol % CO 2 . In another embodiment, the substrate comprises no or substantially no CO 2 . 
     Although the substrate is typically gaseous, the substrate may also be provided in alternative forms. For example, the substrate may be dissolved in a liquid saturated with a CO-containing gas using a microbubble dispersion generator. By way of further example, the substrate may be adsorbed onto a solid support. 
     The substrate and/or C1-carbon source may be a waste gas obtained as a byproduct of an industrial process or from some other source, such as from automobile exhaust fumes or biomass gasification. In certain embodiments, the industrial process is selected from the group consisting of ferrous metal products manufacturing, such as a steel mill manufacturing, non-ferrous products manufacturing, petroleum refining processes, coal gasification, electric power production, carbon black production, ammonia production, methanol production, and coke manufacturing. In these embodiments, the substrate and/or C1-carbon source may be captured from the industrial process before it is emitted into the atmosphere, using any convenient method. 
     The substrate and/or C1-carbon source may be syngas, such as syngas obtained by gasification of coal or refinery residues, gasification of biomass or lignocellulosic material, or reforming of natural gas. In another embodiment, the syngas may be obtained from the gasification of municipal solid waste or industrial solid waste. 
     The composition of the substrate may have a significant impact on the efficiency and/or cost of the reaction. For example, the presence of oxygen (O 2 ) may reduce the efficiency of an anaerobic fermentation process. Depending on the composition of the substrate, it may be desirable to treat, scrub, or filter the substrate to remove any undesired impurities, such as toxins, undesired components, or dust particles, and/or increase the concentration of desirable components. 
     The microorganism of the invention may be cultured to produce one or more products. For instance,  Clostridium autoethanogenum  produces or can be engineered to produce ethanol (WO 2007/117157), acetate (WO 2007/117157), butanol (WO 2008/115080 and WO 2012/053905), butyrate (WO 2008/115080), 2,3-butanediol (WO 2009/151342), lactate (WO 2011/112103), butene (WO 2012/024522), butadiene (WO 2012/024522), methyl ethyl ketone (2-butanone) (WO 2012/024522 and WO 2013/185123), ethylene (WO 2012/026833), acetone (WO 2012/115527), isopropanol (WO 2012/115527), lipids (WO 2013/036147), 3-hydroxypropionate (3-HP) (WO 2013/180581), isoprene (WO 2013/180584), fatty acids (WO 2013/191567), 2-butanol (WO 2013/185123), 1,2-propanediol (WO 2014/0369152), and 1-propanol (WO 2014/0369152). In addition to one or more target products, the microorganism of the invention may also produce ethanol, acetate, and/or 2,3-butanediol. In certain embodiments, microbial biomass itself may be considered a product. 
     A “native product” is a product produced by a genetically unmodified microorganism. For example, ethanol, acetate, and 2,3-butanediol are native products of  Clostridium autoethanogenum, Clostridium ljungdahlii , and  Clostridium ragsdalei . A “non-native product” is a product that is produced by a genetically modified microorganism, but is not produced by a genetically unmodified microorganism from which the genetically modified microorganism is derived. 
     The terms “intermediate” and “precursor,” which may be referred to interchangeably herein, refer to a molecular entity in an enzymatic pathway upstream of an observed or target product. 
     “Selectivity” refers to the ratio of the production of a target product to the production of all fermentation products produced by a microorganism. The microorganism of the invention may be engineered to produce products at a certain selectivity or at a minimum selectivity. In one embodiment, a target product account for at least about 5%, 10%, 15%, 20%, 30%, 50%, or 75% of all fermentation products produced by the microorganism of the invention. In one embodiment, the target product accounts for at least 10% of all fermentation products produced by the microorganism of the invention, such that the microorganism of the invention has a selectivity for the target product of at least 10%. In another embodiment, the target product accounts for at least 30% of all fermentation products produced by the microorganism of the invention, such that the microorganism of the invention has a selectivity for the target product of at least 30%. 
     “Increasing the efficiency,” “increased efficiency,” and the like include, but are not limited to, increasing growth rate, product production rate or volume, product volume per volume of substrate consumed, or product selectivity. Efficiency may be measured relative to the performance of parental microorganism from which the microorganism of the invention is derived. 
     Typically, the culture is performed in a bioreactor. The term “bioreactor” includes a culture/fermentation device consisting of one or more vessels, towers, or piping arrangements, such as a continuous stirred tank reactor (CSTR), immobilized cell reactor (ICR), trickle bed reactor (TBR), bubble column, gas lift fermenter, static mixer, or other vessel or other device suitable for gas-liquid contact. In some embodiments, the bioreactor may comprise a first growth reactor and a second culture/fermentation reactor. The substrate may be provided to one or both of these reactors. As used herein, the terms “culture” and “fermentation” are used interchangeably. These terms encompass both the growth phase and product biosynthesis phase of the culture/fermentation process. 
     The culture is generally maintained in an aqueous culture medium that contains nutrients, vitamins, and/or minerals sufficient to permit growth of the microorganism. Preferably the aqueous culture medium is an anaerobic microbial growth medium, such as a minimal anaerobic microbial growth medium. Suitable media are well known in the art. 
     The culture/fermentation should desirably be carried out under appropriate conditions for production of the target product. Typically, the culture/fermentation is performed under anaerobic conditions. Reaction conditions to consider include pressure (or partial pressure), temperature, gas flow rate, liquid flow rate, media pH, media redox potential, agitation rate (if using a continuous stirred tank reactor), inoculum level, maximum gas substrate concentrations to ensure that gas in the liquid phase does not become limiting, and maximum product concentrations to avoid product inhibition. In particular, the rate of introduction of the substrate may be controlled to ensure that the concentration of gas in the liquid phase does not become limiting, since products may be consumed by the culture under gas-limited conditions. 
     Operating a bioreactor at elevated pressures allows for an increased rate of gas mass transfer from the gas phase to the liquid phase. Accordingly, it is generally preferable to perform the culture/fermentation at pressures higher than atmospheric pressure. Also, since a given gas conversion rate is, in part, a function of the substrate retention time and retention time dictates the required volume of a bioreactor, the use of pressurized systems can greatly reduce the volume of the bioreactor required and, consequently, the capital cost of the culture/fermentation equipment. This, in turn, means that the retention time, defined as the liquid volume in the bioreactor divided by the input gas flow rate, can be reduced when bioreactors are maintained at elevated pressure rather than atmospheric pressure. The optimum reaction conditions will depend partly on the particular microorganism used. However, in general, it is preferable to operate the fermentation at a pressure higher than atmospheric pressure. Also, since a given gas conversion rate is in part a function of substrate retention time and achieving a desired retention time in turn dictates the required volume of a bioreactor, the use of pressurized systems can greatly reduce the volume of the bioreactor required, and consequently the capital cost of the fermentation equipment. 
     Target products may be separated or purified from a fermentation broth using any method or combination of methods known in the art, including, for example, fractional distillation, evaporation, pervaporation, gas stripping, phase separation, and extractive fermentation, including for example, liquid-liquid extraction. In certain embodiments, target products are recovered from the fermentation broth by continuously removing a portion of the broth from the bioreactor, separating microbial cells from the broth (conveniently by filtration), and recovering one or more target products from the broth. Alcohols and/or acetone may be recovered, for example, by distillation. Acids may be recovered, for example, by adsorption on activated charcoal. Separated microbial cells are preferably returned to the bioreactor. The cell-free permeate remaining after target products have been removed is also preferably returned to the bioreactor. Additional nutrients (such as B vitamins) may be added to the cell-free permeate to replenish the medium before it is returned to the bioreactor. 
     EXAMPLES 
     The following examples further illustrate the invention but, of course, should not be construed to limit its scope in any way. 
     Example 1 
     This example demonstrates the ability of Ptb-Buk to convert acetoacetyl-CoA to acetoacetate in  E. coli  in vivo and its use in production of acetone, isopropanol, 3-hydroxybutyrate, and isobutylene 
     Pathways that rely on the Ptb-Buk system for acetoacetate production from acetoacetyl-CoA were designed and constructed. This was done in a modular fashion using a pDUET vector system (Novagen). One module contained ptb-buk genes from  C. beijerinckii  NCIMB8052 (GenBank NC_009617, position 232027 . . . 234147; Cbei_0203-204; NCBI-GeneID 5291437-38) on plasmid pACYC. Another module contained the thiolase gene thlA of  C. acetobutylicum  (Genbank NC_001988, position 82040 . . . 83218; CA_P0078; NCBI-GeneID 1116083) and the acetoacetate decarboxylase gene adc of  C. beijerinckii  NCIMB8052 (Genbank NC_009617, position 4401916 . . . 4402656; Cbei_3835; NCBI-GeneID 5294996) on plasmid pCOLA. Ptb and buk genes were amplified from genomic DNA of  C. beijerinckii  NCIMB8052 and thlA and adc genes from an existing acetone plasmid pMTL85147-thlA-ctfAB-adc (WO 2012/115527) and cloned under control of the T7 promoter present in the pDUET vectors via restriction independent cloning with the circular polymerase extension cloning (CPEC) method (Quan,  PloS One,  4:e6441, 2009). 
     Oligonucleotides Used for Amplification of Ptb and Buk Genes: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 95 
                 pACYCDuet-ptb-buk- 
                 AAGTTTTTACTCATATGTATATC 
                 reverse 
               
               
                   
                 pACYC-ptb-R1 
                 TCCTTCTTATACTTAAC 
               
               
                   
               
               
                 96 
                 pACYCDuet-ptb-buk-ptb- 
                 AGAAGGAGATATACATATGAGT 
                 forward 
               
               
                   
                 pACYC-F1 
                 AAAAACTTTGATGAGTTA 
               
               
                   
               
               
                 97 
                 pACYCDuet-ptb-buk- 
                 ACCAGACTCGAGGGTACCTAGT 
                 reverse 
               
               
                   
                 buk-pACYC-R1 
                 AAACCTTAGCTTGTTC 
               
               
                   
               
               
                 98 
                 pACYCDuet-ptb-buk- 
                 TAAGGTTTACTAGGTACCCTCG 
                 forward 
               
               
                   
                 pACYC-buk-F1 
                 AGTCTGGTAAAGAAAC 
               
               
                   
               
            
           
         
       
     
     Oligonucleotides Used for Amplification of thlA and Adc Genes: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 99 
                 pCOLADuet-thlA-adc- 
                 ACATATGTATATCTCCTTCTTAC 
                 reverse 
               
               
                   
                 thlA-adc-R1 
                 TAGCACTTTTCTAGCAATATTG 
               
               
                   
               
               
                 100 
                 pCOLADuet-thlA-adc- 
                 AGTAAGAAGGAGATATACATAT 
                 forward 
               
               
                   
                 adc-ThlA-F1 
                 GTTAGAAAGTGAAGTATCTAAAC 
               
               
                   
               
               
                 101 
                 pCOLADuet-thlA-adc- 
                 CAGACTCGAGGGTACCTTATTT 
                 reverse 
               
               
                   
                 adc-pCOLA-R1 
                 TACTGAAAGATAATCATGTAC 
               
               
                   
               
               
                 102 
                 pCOLADuet-thlA-adc- 
                 TCTTTCAGTAAAATAAGGTACC 
                 forward 
               
               
                   
                 pCOLA-adc-F1 
                 CTCGAGTCTGGTAAAGAAAC 
               
               
                   
               
               
                 103 
                 pCOLADuet-thlA-adc- 
                 GAAGGAGATATACATATGAAA 
                 forward 
               
               
                   
                 thlA-pCOLA-F1 
                 GAAGTTGTAATAGCTAGTG 
               
               
                   
               
               
                 104 
                 pCOLADuet-thlA-adc- 
                 ACAACTTCTTTCATATGTATATC 
                 reverse 
               
               
                   
                 pCOLA-thlA-R1 
                 TCCTTCTTATACTTAAC 
               
               
                   
               
            
           
         
       
     
     After the plasmids pACYC-ptb-buk (SEQ ID NO: 105) and pCOLA-thlA-adc (SEQ ID NO: 106) were constructed, they were transformed individually and together into  E. coli  BL21 (DE3) (Novagen) and growth experiments carried out in quadruplicates in 1.5 mL cultures in 12-well plates at 28° C. with 160 rpm orbital shaking using M9 minimal medium (Sambrook, Molecular Cloning: A Laboratory Manual, Vol 3, Cold Spring Harbour Press, 1989) with glucose ( FIG. 4 ). The cultures were inoculated at an OD600 nm of 0.1 and induced with different concentrations of IPTG (0, 50, 100 μM) after 2 h of growth ( FIG. 5 ). The plates were sealed using plate tape strips and each well was pierced with a green tipped needle to provide micro-aerobic conditions. Growth was carried out for another 64 h of induction. The experiment was repeated in triplicate. 
     Acetone concentrations, as well as the concentrations of other metabolites such as isobutylene, were measured using gas chromatography (GC) analysis, employing an Agilent 6890N headspace GC equipped with a Supelco polyethylene glycol (PEG) 60-μm solid-phase microextraction fiber, a Restek Rtx-1 (30 m×0.32 μm×5 μm) column, and a flame ionization detector (FID). Samples (4 ml) were transferred into a 20-ml headspace vial, upon which the fiber was incubated (exposed) for 10 min at 50° C. The sample was desorbed in the injector at 250° C. for 9 min. Chromatography was performed with an oven program of 40° C. (5-min hold) and 10° C./min to 200° C., followed by a 5-min hold at 220° C. The column flow rate was 1 ml/min, with hydrogen as the carrier gas. The FID was kept at 250° C., with hydrogen at 40 ml/min, air at 450 ml/min, and nitrogen at 15 ml/min as the makeup gas. 
     It was immediately obvious that acetone was produced in the strain carrying both the pACYC-ptb-buk and pCOLA-thlA-adc plamids (expressing thiolase, Ptb-Buk, and acetoacetate decarboxylase). Average final acetone production of 0.19 g/L was measured, whereas no acetone was produced in a no plasmid control, media control, and single plasmid controls pACYC-ptb-buk (expressing Ptb-Buk) or pCOLA-thlA-adc plamid (expressing thiolase and acetoacetate decarboxylase) (below reliable detection limit). The uninduced culture of the strain carrying both the pACYC-ptb-buk and pCOLA-thlA-adc plamids (expressing thiolase, Ptb-Buk, and acetoacetate decarboxylase) did not produce appreciable amounts of acetone. 
     Average Acetone Production in  E. coli  BL21 (DE3): 
     
       
         
           
               
               
             
               
                   
               
               
                 Strain 
                 Acetone (g/L) 
               
               
                   
               
             
            
               
                 Thl + Ptb-Buk + Adc [ E. coli  BL21 
                 0.19 ± 0.04 
               
               
                 (DE3) + pACYC-ptb-buk + pCOLA-thlA- 
               
               
                 adc] 
               
               
                   
               
               
                 Thl + Adc alone [ E. coli  BL21 (DE3) + 
                 0.04 ± 0.01 
               
               
                 pCOLA-thlA-adc] 
               
               
                   
               
               
                 Ptb-Buk alone [ E. coli  BL21 (DE3) + 
                 0.03 ± 0.01 
               
               
                 pACYC-ptb-buk] 
               
               
                   
               
               
                 No plasmid control [ E. coli  BL21 
                 0.04 ± 0.01 
               
               
                 (DE3)] 
               
               
                   
               
               
                 Media control 
                 0.03 ± 0.01 
               
               
                   
               
            
           
         
       
     
     This experiment clearly demonstrates that Ptb-Buk is able to perform the conversion of acetoacetyl-CoA to acetoacetate can be used in place of a CoA-transferase or a thioesterase for the production of acetone, exemplified using a route that comprises steps 1, 2, and 3 of  FIG. 1 . 
     It is well known that isopropanol can be produced from acetone by addition of a primary:secondary alcohol dehydrogenase (Köpke,  Appl Environ Microbiol,  80: 3394-3403, 2014) (step 4 in  FIG. 1 ) and that isobutylene can be produced from acetone via addition of a hydroxyisovalerate synthase (step 5 in  FIG. 1 ) and decarboxylase (step 6 in  FIG. 1 ) (van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012). A pathway can be constructed that includes the above-demonstrated acetone route via Ptb-Buk with the genes thlA, ptb-buk, and adc and a primary:secondary alcohol dehydrogenase gene (e.g., Genbank accession number NC_022592, pos. 609711 . . . 610766; CAETHG_0553; NCBI-GeneID: 17333984) that would allow isopropanol production via the Ptb-Buk system in  E. coli  comprising steps 1, 2, 3, and 4 of  FIG. 1 . Similarly, a pathway can be constructed that includes the above-demonstrated acetone route via Ptb-Buk conversion of acetoacetyl-CoA to acetoacetate with the genes thlA, ptb-buk, and adc and genes for a hydroxyisovalerate synthase and decarboxylase that would allow isobutylene production via the Ptb-Buk system in  E. coli  comprising of steps 1, 2, 3, 5, and 6 of  FIG. 1 . Acetoacetete can also be converted to 3-hydroxybutyrate via a 3-hydroxybutyrate dehydrogenase Bdh. This can be combined with Ptb-Buk conversion of acetoacetyl-CoA to acetoacetate for 3-hydroxybutyrate production in a strain expressing genes thlA, ptb-buk, and bdh resulting in a pathway comprising steps 1, 2, and 15 of  FIG. 1 . 
     Example 2 
     This example demonstrates the ability of Ptb-Buk to convert acetoacetyl-CoA to acetoacetate in  C. autoethanogenum  in vivo and the use of Ptb-Buk in the production of acetone, isopropanol, 3-hydroxybutyrate, and isobutylene from a gaseous substrate. 
     To demonstrate that the Ptb-Buk system also allows acetone, isopropanol, or isobutylene synthesis from gaseous substrates, a plasmid was constructed that contains the same genes as in Example 1, thl+ptb-buk+adc under control of a clostridial promoter on a shuttle vector that allows expression in acetogens such as  C. autoethanogenum, C. ljungdahlii  or  C. ragsdalei.    
     The pMTL plasmid is a shuttle plasmid system for introducing circular dna into  Clostridia  via  E. coli  conjugation (Heap,  J Microbiol Methods,  78: 79-85, 2009. The genes of interest (i.e., hbd, phaB, thlA, ptb, buk, and aor1) were cloned into the lacZ region of the plasmids using common techniques in molecular biology including dna restriction digestion followed by ligation, and the golden gate dna assembly technology when more than one pieces of dna fragments were to be cloned simultaneously into the plasmid. The constructed plasmids are verified by DNA sequencing. 
     Production of acetone and isopropanol was previously demonstrated in  C. autoethanogenum  using a plasmid pMTL85147-thlA-ctfAB-adc encoding thl+ctfAB+adc (WO 2012/115527) under the control of a clostridial promoter from the Wood-Ljungdahl gene cluster. In this plasmid the ctfAB genes encoding the CoA transferase were replaced directly with ptb-buk genes encoding the Ptb-Buk system. This was done as described in Example 1 using the CPEC method. The resulting plasmid is pMTL85147-thlA-ptb-buk-adc. 
     Oligonucleotides used for the amplification of ptb-buk and cloning into pMTL8317-thl-ptb-buk-adc are described below. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ 
                   
                   
                   
               
               
                 ID 
               
               
                 NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 107 
                 thlA-ptb-R1 
                 ATTTCCTCCCTTTCTAGCACTTT 
                 reverse 
               
               
                   
                   
                 TCTAGCAATATTG 
               
               
                   
               
               
                 108 
                 adc-buk-F1 
                 TAAGGTTTACTAAGGAGGTTGT 
                 forward 
               
               
                   
                   
                 TTTATGTTAGAAAG 
               
               
                   
               
               
                 109 
                 thlA-ptb-F1 
                 GCTAGAAAAGTGCTAGAAAGG 
                 forward 
               
               
                   
                   
                 GAGGAAATGAACATG 
               
               
                   
               
               
                 110 
                 Buk-adc-R1 
                 AAAACAACCTCCTTAGTAAACC 
                 reverse 
               
               
                   
                   
                 TTAGCTTGTTCTTC 
               
               
                   
               
            
           
         
       
     
       C. autoethanogenum  DSM10061 and DSM23693 (a derivate of DSM10061) were sourced from DSMZ (The German Collection of Microorganisms and Cell Cultures, Inhoffenstraße 7 B, 38124 Braunschweig, Germany). 
     Strains were grown at 37° C. in PETC medium at pH 5.6 using standard anaerobic techniques (Hungate,  Meth Microbiol,  3B: 117-132, 1969; Wolfe,  Adv Microb Physiol,  6: 107-146, 1971). 30 psi CO-containing steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ) or a synthetic gas blend with same composition of 44% CO, 32% N 2 , 22% CO 2 , 2% H 2  was used as substrate for autotrophic growth. For solid media, 1.2% bacto agar (BD, Franklin Lakes, N.J. 07417, USA) was added. 
     The construct was synthesized and then transformed into  C. autoethanogenum  via conjugation. For this, the expression vector was first introduced into the conjugative donor strain  E. coli  HB101+R702 (CA434) (Williams,  J Gen Microbiol,  1136: 819-826, 1990) (the donor) using standard heat shock transformation. Donor cells were recovered in SOC medium (Sambrook, Molecular Cloning: A Laboratory Manual, Vol 3, Cold Spring Harbour Press, 1989) at 37° C. for 1 h before being plated on to LB medium (Sambrook, Molecular Cloning: A Laboratory Manual, Vol 3, Cold Spring Harbour Press, 1989) plates containing 100 μg/ml spectinomycin and 25 μg/ml chloramphenicol. LB plates were incubated at 37° C. overnight. The next day, 5 ml LB aliquots containing 100 μg/ml spectinomycin and 25 μg/ml chloramphenicol were inoculated with several donor colonies and incubated at 37° C., shaking for approximately 4 h, or until the culture was visibly dense but had not yet entered stationary phase. 1.5 ml of the donor culture was harvested in a microcentrifuge tube at room temperature by centrifugation at 4000 rpm for 2 min, and the supernatant was discarded. The donor cells were gently resuspended in 500 μl sterile PBS buffer (Sambrook, Molecular Cloning: A Laboratory Manual, Vol 3, Cold Spring Harbour Press, 1989) and centrifuged at 4000 rpm for 2 min and the PBS supernatant was discarded. The pellet was introduced into an anaerobic chamber and gently resuspended in 200 μl during late exponential phase  C. autoethanogenum  culture (the recipient). The conjugation mixture (the mix of donor and recipient cells) was spotted onto PETC-MES+fructose agar plates and left to dry. When the spots were no longer visibly wet, the plates were introduced into a pressure jar, pressurized with syngas to 25-30 psi and incubated at 37° C. for ˜24 h. After 24 h incubation, the conjugation mixture was removed from the plates by gently scraping it off using a 10 μl inoculation loop. The removed mixture was suspended in 200-300 μl PETC medium. 100 μl aliquots of the conjugation mixture were plated on to PETC medium agar plates supplemented 15 μg/ml thiamphenicol to select for transformants bearing the plasmid, which confers resistance to thiamphenicol via expression of chloramphenicol acetyltransferase. 
     Three distinct colonies of  C. autoethanogenum  bearing the pMTL85147-thlA-ptb-buk-adc plasmid were inoculated into 2 mL of PETC-MES medium with 15 μg/ml thiamphenicol and grown autotrophically at 37° C. with 100 rpm orbital shaking for three days. Cultures were diluted to OD 600 nm =0.05 in 10 mL PETC-MES medium with 15 μg/ml thiamphenicol in serum bottles and grown autotrophically at 37° C. with 100 rpm orbital shaking for five days, sampling daily to measure biomass and metabolites. In parallel a control strain was examined where the expression plasmid encoded only thl and adc under the control of the Wood-Ljungdahl cluster promoter, with no ctfAB or ptb-buk genes to catalyse the formation of acetoacetate from acetoacetyl-CoA (pMTL85147-thlA-adc). Cultures were sampled for five days in order to monitor metabolites and biomass accumulation. 
     Isopropanol concentrations as well as concentrations of ethanol, acetic acid, 2,3-butanediol and lactic acid were measured by high-performance liquid chromatography (HPLC) on an Agilent LC with refractive index (RI) detection at 35° C. Samples were prepared by diluting 400 μL with 100 μL of 5-sulfosalicylic acid solution (1% w/v in 1 M sulphuric acid), followed by a 3 minute centrifugation at 14,000 rpm; the supernatant was transferred to a glass vial for analysis. Separation was carried out with a 10 μL injection on to an Alltech IOA-2000 column (150 mm×6.5 mm×8 μm) at 0.7 mL/min and 65° C. under isocratic conditions, using 5 mM sulphuric acid mobile phase. 
     In some instances, a longer HPLC method was used to improve peak separation. In this method, isopropanol, ethanol, acetate, 2,3-butanediol, and also 3-hydroxybutyrate (which is not separated using the shorter method) concentrations were measured by high-performance liquid chromatography (HPLC) on an Agilent 1260 Infinity LC with refractive index (RI) detection at 35° C. Samples were prepared by diluting 400 μL with 100 μL of 5-sulfosalicylic acid solution (1% w/v in 1 M sulphuric acid), followed by a 3 minute centrifugation at 14,000 rpm; the supernatant was transferred to a glass vial for analysis. Separation was carried out with a 10 μL injection on to an Aminex HPX-87H column (300 mm×7.8 mm×9 μm) at 0.6 mL/min and 35° C. under isocratic conditions, using 5 mM sulphuric acid mobile phase. 
       C. autoethanogenum  bearing the pMTL85147-thlA-ptb-buk-adc produced isopropanol up to 0.804 g IPA/g of biomass, whereas control strain  C. autoethanogenum  with pMTL85147-thlA-adc that does not contain Ptb-Buk produced no IPA ( FIG. 12 ). 
     This experiment clearly demonstrates that Ptb-Buk is able to perform the conversion of acetoacetyl-CoA to acetoacetate in the isopropanol pathway when using a gaseous substrate. Ptb-Buk can be used in place of a CoA transferase or a thioesterase in a gas-fermenting acetogen such as  C. autoethanogenum , exemplified using a route that comprises steps 1, 2, 3, and 4 of  FIG. 1 . 
       C. autoethanogenum  contains a native primary:secondary alcohol dehydrogenase that converts acetone to isopropanol (Köpke,  Appl Environ Microbiol,  80: 3394-3403, 2014). It has been demonstrated that knock-out of this gene eliminates conversion of acetone to isopropanol in  C. autoethanogenum  (WO 2015/085015). In background of this knock-out, it becomes possible to produce acetone (rather than isopropanol) via the Ptb-Buk system from a gaseous feedstock, using the same genes comprising steps 1, 2, and 3 of  FIG. 1 . Addition of hydroxyisovalerate synthase and decarboxylase genes (van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012) to this strain would enable isobutylene production from gas in  C. autoethanogenum  or similar bacteria comprising of steps 1, 2, 3, 5, and 6 of  FIG. 1 . 
     Acetoacetate can also be converted to 3-hydroxybutyrate via a 3-hydroxybutyrate dehydrogenase Bdh. A 3-hydroxybutyrate dehydrogenase was identified in the genome of  C. autoethanogenum  (AGY75962) and other acetogens as  C. ljungdahlii  (ADK16920.1). This activity can be combined with Ptb-Buk (or CoA transferase) conversion of acetoacetyl-CoA to acetoacetate for 3-hydroxybutyrate production in a strain expressing genes thlA, ptb-buk (or ctfAB) and bdh resulting a pathway comprising steps 1, 2, and 15 of  FIG. 1 . Low levels of 3-hydroxybutyrate formation (up to 2 g/L) via this route have been demonstrated in  C. autoethanogenum . These levels could be enhanced by overexpressing the Bdh gene that is only expressed in at low levels natively. 
     In one experiment,  C. autoethanogenum  was transformed with plasmid pMTL82256-thlA-ctfAB as described in Example 2. The production was monitored for 10 days from six biological replicates under autotrophic conditions as described in Example 2. The average of 3-HB after 10 days was 1.86±0.14 g/L. At day 10, 1,3-butanediol was produced (from 3-HB) at an average titer of 0.38±0.05 g/L ( FIG. 37 ). No acetone or isopropanol was formed. This demonstrates that 3-HB can be produced efficiently via acetoacetate through native enzymes. 
     In certain embodiments, it may be desirable to knock out or knock down expression of 3-hydroxybutyrate dehydrogenases, such as Bdh, to prevent carbon drain to 3-HB and therefore boost production of products such as acetone, isopropanol, and isobutylene. 
     Example 3 
     This example demonstrates the ability of Ptb-Buk to convert (R)-3-hydroxybutyryl-CoA to (R)-3-hydroxybutyryrate in  E. coli  in vivo for production of (R)-hydroxybutyrate, acetone, isopropanol, or isobutylene. 
     Pathways were designed and constructed that rely on the Ptb-Buk system for (R)-3-hydroxybutyrate production from (R)-3-hydroxybutyryl-CoA. Additionally, a 3-hydroxybutyrate dehydrogenase (Bdh) was utilized for conversion of (R)-3-HB to acetoacetate. It has been reported that  Ralstonia pickettii  have two 3-hydroxybutyrate dehydrogenases Bdh1 and Bdh2 that are able to convert 3-hydroxybutyrate to acetoacetate in vitro (Takanashi,  J Biosci Bioeng,  101: 501-507, 2006). One pathway was designed making use of this enzyme for acetone production (steps 1, 13, 14, 15, 3 of  FIG. 1 ), while recycling the reducing equivalents produced in the production of (R)-3-hydroxybutyryl-CoA and the ATP generated by Ptb-Buk ( FIG. 6 ). 
     The pathways were constructed in a modular fashion using the pDUET vector system (Novagen). The two modules described in example above (pACYC-ptb-buk for expression of Ptb-Buk and pCOLA-thlA-adc for expression of thiolase and acetoacetate decarboxylase) were used together with two additional modules containing either (R)-specific 3-hydroxybutyrate dehydrogenase phaB of  Cupravidus necator  (WP_010810131.1) alone (pCDF-phaB) and one with 3-hydroxybutyrate dehydrogenase bdh1 gene of  Rasltonia pickettii  (BAE72684.1) (pCDF-phaB-bdh1) in vector pCDF. Both phaB and bdh1 gene were synthesized from GeneArt and cloned under control of the T7 promoter present in via restriction independent cloning with the circular polymerase extension cloning (CPEC) method (Quan, PloS One, 4:e6441, 2009). 
     Oligonucleotides Used for Amplification of Bdh1 Gene: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 111 
                 pDuet-insert2-R1 
                 CATATGTATATCTCCTTCTTATA 
                 forward 
               
               
                   
                   
                 CTTAAC 
               
               
                   
               
               
                 112 
                 insert2-pDuet-F1 
                 GTTAAGTATAAGAAGGAGATAT 
                 forward 
               
               
                   
                   
                 ACATATG 
               
               
                   
               
               
                 113 
                 pDuet-insert2-F1 
                 CCTCGAGTCTGGTAAAGAAAC 
                 forward 
               
               
                   
               
               
                 114 
                 insert2-pDuet-R1 
                 GTTTCTTTACCAGACTCGAGG 
                 forward 
               
               
                   
               
            
           
         
       
     
     Oligonucleotides Used for Amplification of phaB Gene: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 115 
                 pCDF-phaB-pACYC- 
                 CTATTCTTTGTGTCATGGTATAT 
                 forward 
               
               
                   
                 phaB-R1 
                 CTCCTTATTAAAG 
               
               
                   
               
               
                 116 
                 pCDF-phaB-phaB- 
                 ATAAGGAGATATACCATGACAC 
                 forward 
               
               
                   
                 pACYC-F1 
                 AAAGAATAGCATAC 
               
               
                   
               
               
                 117 
                 pCDF-phaB-pACYC- 
                 TGGTTTACACATGGGATAAGAT 
                 forward 
               
               
                   
                 phaB-F1 
                 CCGAATTCGAGCTC 
               
               
                   
               
               
                 118 
                 pCDF-phaB-phaB- 
                 AGCTCGAATTCGGATCTTATCC 
                 forward 
               
               
                   
                 pACYC-R1 
                 CATGTGTAAACCAC 
               
               
                   
               
            
           
         
       
     
     After the plasmids pACYC-ptb-buk (SEQ ID NO: 105), pCOLA-thlA-adc (SEQ ID NO: 106), pCDF-phaB (SEQ ID NO: 119) and pCDF-phaB-bdh1 (SEQ ID NO: 120) were constructed, they were transformed individually and in combinations into  E. coli  BL21 (DE3) (Novagen) and growth experiments were carried out in quadruplicate in 1.5 mL cultures in 12-well plates at 28° C. with 160 rpm orbital shaking using M9 minimal medium with glucose. The cultures were inoculated at an OD600 nm of 0.1 and after 2 h of growth induced with different concentrations of IPTG (0, 50, 100 μM). The plates were sealed using BioRad plate tape strips and each well pierced with a green tipped needle to provide micro-aerobic conditions. Growth was carried out for another 64 h of induction. The experiment was repeated 3 times. Metabolites were measured as described in previous examples. 
     Cultures containing a combination of plasmids pACYC-ptb-buk, pCOLA-thlA-adc and pCDF-phaB produced between 1.65-2.4 g/L (R)-3-hydroxybutyrate (depending on level of inducer), with only very small amounts of byproducts ( FIGS. 13A-F ), demonstrating the efficiency of the Ptb-Buk system to convert (R)-3-hydroxybutyryl-CoA to (R)-3-hydroxybutyryrate and support growth ( FIG. 13A-F ). In cultures that also expressed bdh1 (containing a combination of plasmids pACYC-ptb-buk, pCOLA-thlA-adc, and pCDF-phaB-bdh1) only small amounts of (R)-3-hydroxybutyryrate were found in the culture media, while between 0.89-1.16 g/L acetone was found (depending on level of inducer), indicating that bdh1 gene is efficient in converting (R)-3-hydroxybutyrate to acetoacetate and further to acetone. In all plasmid combinations that lack Ptb-Buk, no 3-hydroxybutyrate or acetone was found ( FIG. 13A-F ). In these cultures, acetate levels were significantly higher. 
     This experiment clearly demonstrates that Ptb-Buk is able to perform the conversion of (R)-3-hydroxybutyrate-CoA to 3-hydroxybutyrate and also that Bdh1 is able in vivo to convert 3-hydroxybutyrate further to acetoacetate by recycling the reducing equivalents produced in the production of (R)-3-hydroxybutyryl-CoA. The experiment also highlights that Ptb-Buk is able to support growth and therefore acetate production becomes unnecessary. Production of (R)-3-hydroxybutyrate formation was exemplified in a strain that comprises steps 1, 13, and 14 of  FIG. 1 . Production of acetone was exemplified via a route that comprises steps 1, 13, 14, 15, and 3 of  FIG. 1 . 
     It is well known that isopropanol can be produced from acetone by addition of a primary:secondary alcohol dehydrogenase (step 4 in  FIG. 1 ) (Köpke,  Appl Environ Microbiol,  80: 3394-3403, 2014) and that isobutylene can be produced from acetone via addition of a hydroxyisovalerate synthase (step 5 in  FIG. 1 ) and decarboxylase (step 6 in  FIG. 1 ) (van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012). A pathway can be constructed that includes the above-demonstrated acetone route via Ptb-Buk with the genes thlA, ptb-buk, and adc and a primary:secondary alcohol dehydrogenase gene (e.g., Genbank NC_022592, pos. 609711 . . . 610766; CAETHG_0553; NCBI-GeneID: 17333984) that would allow isopropanol production via the Ptb-Buk system in  E. coli  (steps 1, 13, 14, 15, 3, and 4 of  FIG. 1 ). Similarly, a pathway can be constructed that includes the above-demonstrated acetone route via Ptb-Buk with the genes thlA, ptb-buk, and adc and genes for a hydroxyisovalerate synthase and decarboxylase that would allow isobutylene production via the Ptb-Buk system in  E. coli  (steps 1, 13, 14, 15, 3, 5, and 6 of  FIG. 1 ). 
     Example 4 
     This example demonstrates the production of (R)-3-hydroxybutyrate and 1,3-butanediol in  C. autoethanogenum . It also demonstrates production of 1,3-butanediol in absence of 2,3-butanediol. 
     A strain of  C. autoethanogenum  was constructed in which the native pathway for 2,3-butanediol production was inactivated and replaced with genes for (R)-3-hydroxybutyryl-CoA formation. This was achieved by replacing the acetolactate decarboxylase gene (budA) on genome of  C. autoethanogenum  with genes for thiolase (thlA of  C. acetobutylicum ; GenBank NC_001988, position 82040 . . . 83218; CA_P0078; NCBI-GeneID 1116083) and (R)-specific 3-hydroxybutyrate dehydrogenase (phaB of  Cupravidus necator ; GenBank WP_010810131.1) resulting in strain  C. autoethanogenum  budA::thlAphaB. 
     To replace budA gene with thlA and phaB genes a plasmid, pMTL8225-budA::thlA-phaB ( FIG. 14 ), with  E. coli  toxin gene mazF under tet3n0 tetracycline inducible promoter (for counter selection), ˜1 kb upstream homology arm of budA gene, thlA, phaB, ermB cassette flanked by loxP sites and ˜1 kb downstream homology arm of budA gene were assembled on plasmid pMTL-tet3no. 
     The ˜1 kb upstream and downstream homology arms of budA were PCR amplified from  C. autoethanogenum  with primers SN01/SN02 and SN07/SN08. thlA and phaB genes were PCR amplified from genomic DNA of  Cupriavidus necator  using primers SN03/SN04mod. The ermB cassette flanked with loxP sites was PCR amplified using primers SN05mod/SN06. tet3no promoter flanked by FseI and PmeI was synthesized and treated with restriction enzymes FseI and PmeI and cleaned. The PCR products and digested vector were assembled using GeneArt Seamless cloning kit from Life Technologies and plasmid pMTL8225-budA::thlA-phaB (SEQ ID NO: 121) with no mutations in the inserted fragments was used to transform  C. autoethanogenum  by conjugation as described in previous examples. 
     Following conjugation and selection on trimethoprim and clarithromycin, 9 colonies were streaked twice on PETC-MES agar plates with clarithromycin and anhydrotetracycline to induce the expression of mazF genes. The colonies from clarithromycin and anhydrotetracycline should have the budA genes replaced with thlA and phaB genes and ermB cassette. This was verified by PCR using primers Og31f/Og32r flanking the homology arms and KAPA polymerase ( FIG. 15 ). 
     While a band of ˜3.3 kb is amplified from the wild type strain, bands of ˜5.7 kb were amplified from colonies 1, 4, 7 and 9 indicating the replacement of budA gene with thlA, phaB and ermB cassette. The above event was further confirmed by sequencing the PCR products of all 4 clones. With the resulting modification the expression of thlA and phaB genes is driven by the promoter upstream of budA gene. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
               
               
                 NO: 
                 Description 
                 Sequence 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 122 
                 SN01 
                 ATTTACAAATTCGGCCGGCCTACCTCCTCGTATAAATAAGATG 
               
               
                   
               
               
                 123 
                 SN02 
                 CTAGCTATTACAACTTCTTTCATATTACATTCACCTCTATGTC 
               
               
                   
               
               
                 124 
                 SN03 
                 GACATAGAGGTGAATGTAATATGAAAGAAGTTGTAATAGCTAG 
               
               
                   
               
               
                 125 
                 SN04mod 
                 GTATAGCATACATTATACGAACGGTATTATCCCATGTGTAAACC 
               
               
                   
                   
                 ACCGT 
               
               
                   
               
               
                 126 
                 SN05mod 
                 TTCGTATAATGTATGCTATACGAAGTTATCCTTAGAAGCAAACT 
               
               
                   
                   
                 TAAG 
               
               
                   
               
               
                 127 
                 SN06 
                 GTCTAGTGTTTTTTTCTATCAATACTCTAGATACCGTTCGTATAGC 
               
               
                   
               
               
                 128 
                 SN07 
                 TGTATGCTATACGAACGGTAAGTATTGATAGAAAAAAACACTA 
               
               
                   
                   
                 GAC 
               
               
                   
               
               
                 129 
                 SN08 
                 CAAAAAGGAGTTTAAACAAAAAGTCATAAACCTGGATAAC 
               
               
                   
               
               
                 130 
                 Og31f 
                 CCGTTTCTCACAACAACAATACCAG 
               
               
                   
               
               
                 131 
                 Og32r 
                 AAACCACCTTGACGATGAAACCATA 
               
               
                   
               
            
           
         
       
     
     A fermentation with  C. autoethanogenum  budA::thlA-phaB strain was carried out. The culture was grown at 37° C. under synthetic gas (50% CO, 18% CO 2 , 2% H 2 , and 30% N 2 ) that was continuously fed into the bioreactor. The gas flow was initially set at 50 ml/min, increasing to 400 ml/min over the course of the experiment, while the agitation was increased from 200 rpm to 500 rpm. The fermentation was carried out for close to 5 days. Metabolites were measured as described in examples above. 
     The concentration of 1,3-butanediol and other metabolites, such as 2-hydroxyisobutyric acid, were measured using gas chromatography (GC) analysis, employing an Agilent 6890N GC equipped a Agilent CP-SIL 5CB-MS (50 m×0.25 μm×0.25 μm) column, autosampler and a flame ionization detector (FID). Samples were prepared by diluting 400 μL of sample with 400 μL of acetonitrile, followed by a 3 minute centrifugation at 14,000 rpm; the supernatant was transferred to a glass vial and the sample was dried in a Thermo SpeedVac. Once dry, the samples were then suspended in a solution of 400 μL of N,O-Bistrifluoroacetamide (BSTFA) and pyridine (3:1 ratio) and heated in a sealed glass vial for 60 minutes at 60° C. Samples were transferred to an autosampler for analysis using a 1 μL injection, a split ration of 30 to 1, and an inlet temperature of 250° C. Chromatography was performed with an oven program of 70° C. (no hold) to a ramp of 3° C./min to 110° C. to a ramp of 15° C./min to 230° C., followed by a final ramp of 40° C./min to 310° C. with a 3-min hold. The column flow rate was 1.8 ml/min, with helium as the carrier gas. The FID was kept at 320° C., with hydrogen at 40 ml/min, air at 400 ml/min, and helium at 20 ml/min as the makeup gas. 
     Surprisingly, up to 1.55 g/L 3-hydroxybutyrate was produced from gas in a  C. autoethanogenum  budA::thlA-phaB strain expressing thlA and phaB ( FIG. 16 ). A native thioesterase may convert the formed 3-hydroxybutyryl-CoA to 3-hydroxybutyrate. In the genome sequence, three putative thioesterases were identified. 
     Even more surprising, it was also found that, along 3-hydroxybutyrate formation, there was also 1,3-butanediol formation of up to 150 mg/L ( FIG. 16 ). This may be due to native aldehyde:ferredoxin oxidoreductase (AOR) and alcohol dehydrogenase activity. Two AOR genes and several alcohol dehydrogenases are present in the genome of  C. autoethanogenum  (Mock,  J Bacteriol,  197: 2965-2980, 2015). This reduction of 3-hydroxybutyrate is powered by reduced ferredoxin and thus can be directly coupled to CO oxidation, which provides reduced ferredoxin (CO+Fd ox →CO 2 +Fd red ) ( FIG. 7 ). 
     1,3-BDO production was also demonstrated from gas via an alternative route using a butyraldehyde dehydrogenase Bld from  Clostridium saccharoperbutylacetonicum  (AAP42563.1) (SEQ ID NO: 80). The bld gene was synthesized and cloned together with the same thiolase (thlA of  C. acetobutylicum ) and (R)-specific 3-hydroxybutyrate dehydrogenase (phaB of  Cupravidus necator ) into a plasmid pMTL8315-Pfdx-thlA-phaB-bld (SEQ ID NO: 132). Bld and phaB genes were amplified from the above plasmid via primers in table below and cloned into existing plasmid pMTL85147-thlA (WO 2012/115527). 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
                   
               
               
                 NO: 
                 Primer 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 133 
                 bld-phaB-F1 
                 ACATGGGATAAGAAGGAGATATACATATGAT 
                 forward 
               
               
                   
                   
                 AAAAG 
               
               
                   
               
               
                 134 
                 bld-pMTL-R1 
                 CGTCGACTCTAGATTAACCTGCTAAAACACAT 
                 forward 
               
               
                   
                   
                 CTTC 
               
               
                   
               
               
                 135 
                 pMTL-bld-F1 
                 GTGTTTTAGCAGGTTAATCTAGAGTCGACGTC 
                 forward 
               
               
                   
                   
                 ACGC 
               
               
                   
               
            
           
         
       
     
     The resulting construct was transformed into  C. autoethanogenum  as described above and a growth experiment was conducted in serum bottles with 50-mL PETC media and pressurized at 30 psi with CO-containing steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ) or a synthetic gas blend with same composition of 44% CO, 32% N 2 , 22% CO 2 , 2% H 2 . 
     1,3-BDO production was demonstrated via this route from gas ( FIG. 17A ), but production was less (up to 67 mg/L 1,3-BDO) than via the AOR route and, in contrast to the AOR route, growth was impacted when expressing the bld gene comparing to the  C. autoethanogenum  wild-type ( FIG. 17B ). 
     In another experiment,  C. autoethanogenum  transformed with plasmid pMTL83159-phaB-thlA as described in Example 2 produced 0.33 and 0.46 g/L of 3-HB and 1,3-BDO, respectively, in a bottle experiment under autotrophic conditions as described in Example 2 ( FIG. 40 ). 
     Example 5 
     This example demonstrates the production of (S)-3-hydroxybutyrate and 1,3-butanediol in  C. autoethanogenum.    
     A plasmid was constructed that expresses a thiolase (thlA from  C. acetobutylicum ; SEQ ID NO: 136) and an (S)-specific 3-hydroxybutyrate dehydrogenase (hbd1 from  C. kluyveri ; SEQ ID NO: 137) under either a ferredoxin promoter (P fdx  isolated from  C. autoethanogenum ; SEQ ID NO: 138) or a pyruvate-ferredoxin oxidoreductase promoter (P pfor  isolated from  C. autoethanogenum ; SEQ ID NO: 139). The plasmid was constructed as follows: P-hbd1-rbs2-thlA and pieced together and cloned into the pMTL83151 vector (Heap,  J Microbiol Meth,  78: 79-85, 2009) by routine methods in molecular cloning, including restrictive enzyme digestion followed by ligation, overlap extension polymerase chain reaction, seamless cloning (Thermo Fisher Scientific), and GeneArt Type IIs (Thermo Fisher Scientific). The operon P-hbd1-rbs2-thlA was cloned in between restriction sites NotI and XhoI found in the multiple cloning region of the plasmid. P is the constitutive promoter which contains an intact ribosome binding site (rbs). rbs2 (SEQ ID NO: 140) is the ribosome binding site for expressing thlA. The stepwise procedures were amplification of the P, hbd1, and thlA from existing templates with primers listed below. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 141 
                 Pfdx-F1 
                 AAAGGTCTCCGGCCGCGCTCACTATCTGCG 
                 forward 
               
               
                   
                   
                 GAACC 
               
               
                   
               
               
                 142 
                 Pfdx-R1 
                 TTTGGTCTCGAATTCTGTAACACCTCCTTAA 
                 reverse 
               
               
                   
                   
                 TTTTTAG 
               
               
                   
               
               
                 143 
                 Ppfor-F1 
                 AAAGGTCTCCGGCCGCAAAATAGTTGATAA 
                 forward 
               
               
                   
                   
                 TAATGCAGAG 
               
               
                   
               
               
                 144 
                 Ppfor-R1 
                 TTTGGTCTCGAATTCCTCTCCTTTTCAAGCAT 
                 reverse 
               
               
                   
                   
                 ATA 
               
               
                   
               
               
                 145 
                 hbd1-F1 
                 AAAGGTCTCGAATTCAAAGATCTATGTCTAT 
                 forward 
               
               
                   
                   
                 TAAATCAGTTGCAG 
               
               
                   
               
               
                 146 
                 hbd1-R1 
                 TTTGGTCTCCCTCCTTTCTATTTCTAATATGC 
                 reverse 
               
               
                   
                   
                 GAAAAATCCTTTACC 
               
               
                   
               
               
                 147 
                 thlA-F1 
                 AAAGGTCTCAGGAGGTGTTACATATGAAAG 
                 forward 
               
               
                   
                   
                 AAGTTGTAATAGCTAGTGC 
               
               
                   
               
               
                 148 
                 thlA-R1 
                 TTTGGTCTCCTCGAGTATGGATCCCTAGCAC 
                 reverse 
               
               
                   
                   
                 TTTTCTAGCAATATTGC 
               
               
                   
               
            
           
         
       
     
     The polymerase chain reactions were performed as follow using Kapa Taq PCR Kit (Kapa Biosystems). Set annealing temperature at 56° C., and extension for 1 minute. Repeat PCR reaction for 30 cycles. Afterwards, PCR products were desalted using the DNA Clean &amp; Concentrator Kit (Zymo Research Corporation). 
     pMTL83151 plasmid backbone was prepared by carrying out the NotI/XhoI double digestion using the FastDigest NotI and FastDigest XhoI (Thermo Fisher Scientific) following the protocol provided, followed by treatment with alkaline phosphate, using the FastAP Alkaline Phosphatase (Thermo Fisher Scientific) and the protocols provided. The digested backbone was then desalted with the DNA Clean &amp; Concentrator Kit (Zymo Research Corporation). 
     The assembly of the PCR products and the plasmid backbone was carried out using the GeneArt Type IIs Kit (Thermo Fisher Scientific). The resulting plasmid was then isolated from the  E. coli  plasmid expression host using the QIAprep Spin Miniprep Kit (Qiagen). 
     To introduce the assembled plasmids pMTL8315-Pfdx-hbd1-thlA and pMTL8315-Ppfor-hbd1-thlA consisting of the operons, the plasmid was first introduced into the  E. coli  CA434 strain by chemical transformation. Afterwards, conjugation was performed by mixing the transformed CA434 strain with a  C. autoethanogenum  production host on a solid LB-agar media, and incubation in an anaerobic environment under pressure with a mix consisting of carbon monoxide and hydrogen as described in Example 2.  C. autoethanogenum , after conjugation, was selected by successive growth on the solid media containing the proper antibiotic and trimethroprim to remove the remaining  E. coli  CA434 strain, under the anaerobic conditions. 
     The  C. autoethanogenum  strains carrying the introduced pMTL8315-Pfdx-hbd1-thlA or pMTL8315-Ppfor-hbd1-thlA plasmids consisting of the operon P-hbd1-rbs2-thlA were grown in a 10-mL PETC media in a 250-mL Schott bottle, sealed tight with rubber septum and cap, and pressurized at 30 psi with CO-containing steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ) or a synthetic gas blend with same composition of 44% CO, 32% N 2 , 22% CO 2 , 2% H 2 . Metabolites were measured as described in previous examples. 
     Surprisingly, there was 3-hydroxybutyrate produced from gas in  C. autoethanogenum  cultures expressing thlA and hbd1 ( FIG. 18A ). A native thioesterase may convert the formed 3-hydroxybutyryl-CoA to 3-hydroxybutyrate. In the genome sequence, three putative thioesterases were identified. In the strain carrying pMTL8315-Pfdx-hbd1-thlA up to 2.55 g/L 3-hydroxybutyrate was found ( FIG. 18A ). 
     Even more surprising, it was also found that 3-hydroxybutyrate is over time converted to 1,3-butanediol, at the end of growth up to 1.1 g/L 1,3-butanediol was produced in strain carrying plasmid pMTL8315-Pfdx-hbd1-thlA ( FIG. 18A ). This may be due to native aldehyde:ferredoxin oxidoreductase (AOR) and alcohol dehydrogenase activity. Two AOR genes and several alcohol dehydrogenases are present in the genome of  C. autoethanogenum  (Mock,  J Bacteriol,  197: 2965-2980, 2015). This reduction of 3-hydroxybutyrate (and reduction of acetate to ethanol;  FIG. 18B ) is powered by reduced ferredoxin and thus can be directly coupled to CO oxidation, which provides reduced ferredoxin (CO+Fd ox →CO 2 +Fd red ) ( FIG. 7 ). 
     The same strain of  C. autoethanogenum  carrying plasmid pMTL8315-Pfdx-hbd1-thlA was also tested in continuous fermentation. Fermentation was carried out as described in previous example, but the culture was turned continuos with a dilution rate with fresh media of around 0.05 at day 2 and then increased to 1.0 at day 3. High 3-hydroxybutyrate production of up to 7 g/L was observed with 1,3-BDO production of 0.5 g/L. 
     To improve production of (S)-3-hydroxybutyrate and 1,3-butanediol and avoid synthesis of another form of butanediol (2,3-butanediol), plasmid pMTL-HBD-ThlA was introduced into a strain that has an inactivated 2,3-butanediol pathway where the acetolactate decarboxylase gene BudA has been deleted (U.S. Pat. No. 9,297,026). This budA knockout eliminated the major pathway to 2,3-BDO, increasing the specificity for 3-HB and 1,3-BDO production. When pMTL-HBD-ThlA was expressed in the budA deletion strain, a total of 15% C-mol was achieved for both 3-HB and 1,3-BDO ( FIG. 41 ). 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Selectivity 
               
               
                   
                 (C-mol %) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Acetate 
                 14.7 
               
               
                   
                 Ethanol 
                 64.9 
               
               
                   
                 2,3-BDO 
                 1.3 
               
               
                   
                 Biomass 
                 3.7 
               
               
                   
                 3-HB 
                 10.4 
               
               
                   
                 1,3-BDO 
                 5.0 
               
               
                   
               
            
           
         
       
     
     As a comparison, in a strain expressing the same plasmid, pMTL83159-hbd-thlA without budA knockout, the total specificity for the production of 3-HB and 1,3-BDO at the steady state was only 6.9% 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Selectivity 
               
               
                   
                 (C-mol %) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Acetate 
                 0.4 
               
               
                   
                 Ethanol 
                 84.3 
               
               
                   
                 2,3-BDO 
                 6.2 
               
               
                   
                 Biomass 
                 2.2 
               
               
                   
                 3-HB 
                 3.5 
               
               
                   
                 1,3-BDO 
                 3.4 
               
               
                   
               
            
           
         
       
     
     Example 6 
     This example demonstrates that the Ptb-Buk system is efficient in  C. autoethanogenum  on a range of acyl-CoAs including acetoacetyl-CoA, 3-hydroxybutyryl-CoA, and 2-hydroxyisobutyryl-CoA 
     The Ptb-Buk system was expressed from a plasmid in  C. autoethanogenum  and its activity measured using a CoA hydrolysis assay. For this, ptb-buk genes from  C. beijerinckii  NCIMB8052 (GenBank NC_009617, position 232027 . . . 234147; Cbei_0203-204; NCBI-GeneID 5291437-38) were amplified from genomic DNA of  C. beijerinckii  NCIMB8052 and cloned under control of a pyruvate-ferredoxin oxidoreductase promoter (P pfor  isolated from  C. autoethanogenum ; SEQ ID NO: 139) into pMTL82251 vector ((Heap,  J Microbiol Meth,  78: 79-85, 2009) by routine methods in molecular cloning, including restrictive enzyme digestion followed by ligation, overlap extension polymerase chain reaction, seamless cloning (Thermo Fisher Scientific), and GeneArt Type IIs (Thermo Fisher Scientific) as described in Example 5. Oligonucleotides are described below. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
                   
               
               
                 NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 149 
                 Ppfor-F2 
                 aaacagctatgaccgcGGCCGCAAAATAGT 
                 forward 
               
               
                   
               
               
                 150 
                 Ppfor-R2 
                 ttactcatTGGATTCCTCTCCTTT 
                 reverse 
               
               
                   
               
               
                 151 
                 Ptb-Buk-F2 
                 ggaatccaATGAGTAAAAACTTTGATGAG 
                 forward 
               
               
                   
               
               
                 152 
                 Ptb-Buk-R2 
                 caggcctcgagatctcCTAGTAAACCTTAGCTTGTTC 
                 reverse 
               
               
                   
               
            
           
         
       
     
     The resulting plasmid pMTL82256-ptb-buk (SEQ ID NO: 153) was introduced into  C. autoethanogenum  as described in previous examples. 
     Acyl-CoA hydrolysis assays were performed as follows.  C. autoethanogenum  cells were harvested at OD 2 (late exponential phase) by centrifugation (14,000 rpm for 1 min at 4° C.). Cells were re-suspended in 500 μl lysis buffer (potassium phosphate buffer, pH 8). Cells were lysed using a freeze thaw cycle (optional), sonication 6×30 s at amplitude 20 on ice. Samples were centrifuged for 10 min at 14,000 rpm at 4° C. and the supernatant with soluble proteins was removed. The protein concentration was measured, e.g., with a Bradford assay. 
     The assay mix contained: 484 μl of potassium phosphate buffer pH 8.0, 1 μl of DTNB (final concentration of 0.1 mM), 10 μl of cell lysate, and 5 μl of CoA (final concentration of 500 μM). All the components were mixed in a quartz cuvette (1 ml cuvette with a read length of 1 cm) except the protein. The assay was started by adding the cell lysate and following the reaction in a spectrophotometer at 405 nm, 30° C. for 3 min. A control without lysate was run to measure autolysis of the acyl-CoA. 
     To determine activity, slope on the linear part of the curve (usually in the first 30 s), was calculated. The protein amount was normalized and slope was divided by protein amount. An extinction coefficient (14,150 M −1  cm −1 ) was used to calculate the specific activity in M/s/mg. The activity of the negative control was subtracted. 
     The assay was performed with acetoacetyl-CoA, a racemic mix of 3-hydroxybutyryl-CoA (3-HB-CoA) and 2-hydroxyisobutyryl-CoA (2-HIB-CoA). The possibility of artificially low hydrolysis rates for 3-HB-CoA and 2-HIB-CoA due to potential substrate limitation was addressed by repeating the hydrolysis assays for  C. autoethanogenum  lysates using different concentrations of acyl-CoA, 500 μM and 200 μM. 
     The results of the assay show significantly increased CoA hydrolysis in lysates of  C. autoethanogenum  carrying plasmid pMTL82256-ptb-buk expressing the Ptb-Buk system on a range of acyl-CoAs including acetoacetyl-CoA, 3-hydroxybutyryl-CoA and 2-hydroxyisobutyryl-CoA ( FIGS. 20A-B ). Notably, there is also CoA hydrolysis for acyl-CoAs as 2-hydroxyisobutyryl-CoA that are not hydrolysed by the  C. autoethanogenum  wild-type. With acetoacetyl-CoA and 3-hydroxybutyryl-CoA some native CoA hydrolysis activity was observed. 
     Example 7 
     This example demonstrates the disruption of identified native thioesterase genes improve efficiency of the Ptb-Buk and CoA transferase system by increasing the pool of available acyl-CoAs such as acetoacetyl-CoA, 3-hydroxybutyryl-CoA or 2-hydroxyisobutyryl-CoA. 
     In contrast to the Ptb-Buk system, where energy is conserved in the form of ATP during conversion of acyl-CoAs to their respective acids, no energy is conserved if the CoAs are simply hydrolyzed. 
     In hydrolase assays it was found that there is native hydrolysis activity for acetoacetyl-CoA and 3-hydroxybutyryl-CoA in  C. autoethanogenum.    
     Acyl-CoA hydrolysis assays with acetoacetyl-CoA, a racemic mix of 3-hydroxybutyryl-CoA (3-HB-CoA) and 2-hydroxyisobutyryl-CoA (2-HIB-CoA were performed as described in previous example. The results of the assay show cleavage of acetoacetyl-CoA and 3-HB-CoA, but not 2-HIB-CoA, and confirm native activity is present in  C. autoethanogenum  ( FIG. 11 ). 
     An analysis of the genome of  C. autoethanogenum  led to identification of three putative CoA-thioesterases (thioester-hydrolases) that could be responsible for to the cleavage of acetoacetyl-CoA or 3-hydroxybutyryl-CoA thioester bond. These are also present in other acetogens such as  C. ljungdahlii . 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 SEQ 
                   
                 SEQ 
               
               
                   
                   
                   
                 ID 
                   
                 ID 
               
               
                 Description 
                 Annotation 
                 
                   C. autoethanogenum 
                 
                 NO: 
                 
                   C. ljungdahlii 
                 
                 NO: 
               
               
                   
               
             
            
               
                 thioesterase 1 
                 Palmitoyl-CoA 
                 AGY74947.1 
                 154 
                 ADK15695.1 
                 157 
               
               
                 (CAETHG_0718) 
                 hydrolase 
                   
                   
                   
                   
               
               
                 thioesterase 2 
                 4-Hydroxybenzoyl- 
                 AGY75747.1 
                 155 
                 ADK16655.1 
                 158 
               
               
                 (CAETHG_1524) 
                 CoA thioesterase 
                   
                   
                   
                   
               
               
                 thioesterase 3 
                 Putative 
                 AGY75999.1 
                 156 
                 ADK16959.1 
                 159 
               
               
                 (CAETHG_1780) 
                 Thioesterase 
               
               
                   
               
            
           
         
       
     
     Inactivation of these three putative CoA-thioesterases lead to higher product titers, improving efficiency of the Ptb-Buk system. The three putative thioesterases were inactivated using ClosTron technology. In brief, the targeting domain of the type II Ltr was reprogrammed using the ClosTron website and the retargeted ClosTron plasmids were ordered from DNA 2.0. The ClosTron knock out vectors pMTL007C-E2-Cau-2640-571s targeting the thioesterase 1 (CAETHG_0718), pMTL007C-E2-PBor3782-166s targeting the thioesterase 2 (CAETHG_1524), and pMTL007C-E2-PBor4039-199s targeting the thioesterase 3 (CAETHG_1780) were introduced into  C. autoethanogenum  using conjugation. 
     Selection for integration was done by selecting PETC supplemented with 5 μg/ml clarithromycin and successful inactivation by integration of the type II intron was confirmed by PCR across the insertion site. 
     The CoA hydrolase activity on acetoacetyl-CoA of both wild type  C. autoethanogenum  and each of the  C. autoethanogenum  with one of the putative genes inactivated was measured using the assay described above. It was shown that all three strains with the inactivated putative thioesterases showed less hydrolysis activity on acetoacetyl-CoA and 3-hydroxybutyryl-CoA ( FIGS. 21A-B ). 
     To demonstrate that the decreased CoA hydrolase activity, and thus an increased pool in acetoacetyl-CoA, is beneficial for production of acetoacetyl-CoA derived products, the isopropanol plasmid pMTL85147-thlA-ctfAB-adc encoding thl+ctfAB+adc (WO 2012/115527) was introduced into the  C. autoethanogenum  wild-type strain and the strain with inactivated thioesterase 1. A growth experiment was carried out 40 ml PETC medium in 1 L Schott bottles in technical triplicates with Co gas at 37° C. at 110 rpm shaking. Synthetic gas (50% CO, 18% CO 2 , 2% H 2 , and 30% N 2 ) was used as sole energy and carbon source. Headspace exchanged once and gassed to 21 psi (1.5 bar) at 37° C. under synthetic gas (50% CO, 18% CO 2 , 2% H 2 , and 30% N 2 ). Samples for OD and analytics were taken twice a day. 
     The strain with inactivated thioesterase 3 CAETHG_1780 produced significantly higher levels of isopropanol than the wild-type ( FIG. 22  and  FIGS. 23A-D ). 
     Similarly, knockout of thioesterases in  C. autoethanogenum  would increase the pool of 3-hydroxybutyryl-CoA, allowing more efficient utilization of 3-hydroxybutyryl-CoA by Ptb-Buk and leading to higher production of acetone, isopropanol, isobutylene, (R)-3-hydroxybutyrate, 1,3-butanediol, and/or 2-hydroxyisobutyric acid. When plasmid pMTL8315-Pfdx-hbd1-thlA of Example 5 was introduced into  C. autoethanogenum  strain with interrupted thioesterase 2 CAETHG_1524, 3-hydroxybutyrate synthesis was abolished (compared to the up to 2.55 g/L 3-hydroxybutyrate that were found when expressing this plasmid in the  C. autoethanogenum  wild type strain). No competing activity for 3-hydroxybutyryl-CoA is present in this strain. 
     These results demonstrate that by reducing thioesterase activity, a higher CoA pool for the Ptb-Buk system and product synthesis is available. 
     Additionally, the production of 3-HB and 1,3-BDO can be increased by overexpression of ptb-buk. In a control experiment, whereby  C. autoethanogenum  as described in Example 2 was transformed with plasmids pMTL83159-phaB-thlA from Example 4 plus pMTL82256 (Heap,  J Microbiol Methods,  78: 79-85, 2009), in which the latter is an empty plasmid used as a background control, the fermentation of such strain resulted in a production of 3-HB with highest titer at 1.68 g/L at day 10 ( FIG. 42A ). When pMTL82256-buk-ptb, instead of the empty plasmid pMTL82256, was coexpressed with pMTL83159-phaB-thlA in  C. autoethanogenum , the fermentation resulted in a higher titter of 3-HB, at 4.76 g/L, at an earlier time, day 4 ( FIG. 42B ). 
     Deletion of native thioesterases enhances the efficiency of the ptb-buk system, which has preference for (R)-3-HB-CoA. The locus of the thioesterase gene in the genome was deleted and replaced with the buk-ptb dna fragment via the common molecular biology technique known as homologous recombination. The substitution of the thioesterase gene by the buk-ptb was confirmed by PCR, followed by agarose gel electrophoresis and dna sequencing. 
     In a bottle experiment, when pMTL83156-phaB-thlA was expressed without ptb-buk in the thioesterase deletion mutant, described above, the average maximum titer of 3-HB produced was 0.50±0.05 g/L, similar to the titer obtained using an unmodified  C. autoethanogenum  strain. When pMTL82256-buk-ptb was coexpressed with the pMTL83156-phaB-thlA plasmid in a thioesterase knockout strain, the production of 3-HB increased to 1.29±0.10 g/L ( FIG. 43 ). 
     Example 8 
     This example demonstrates that it is possible to eliminate acetate production system in an acetogen  C. autoethanogenum  with the Ptb-buk system. 
     All acetogenic microorganisms are described to produce acetate (Drake, Acetogenic Prokaryotes, In:  The Prokaryotes,  3 rd  edition, pages 354-420, New York, N.Y., Springer, 2006) as the production of acetate provides the microorganism with an option to directly generate ATP from substrate level phosphorylation via Pta (phosphotransacetylase) and Ack (phosphotransacetylase-acetate kinase). Native acetate-forming enzymes such as Pta-Ack are therefore considered to be essential in acetogens (Nagarajan,  Microb Cell Factories,  12: 118, 2013). Since Ptb-Buk provides an alternative means for energy generation, it becomes possible to replace the native Pta-Ack system with Ptb-Buk. 
     The pta and ack genes in  C. autoethanogenum  are in one operon. To replace pta and ack genes with ptb and buk genes a plasmid, pMTL8225-pta-ack::ptb-buk ( FIG. 24 ), with mazF counter selection marker that is under tetracycline inducible promoter, ˜1 kb upstream homology arm, ptb, buk, ermB cassette flanked by loxP sites and ˜1 kb downstream homology arm was assembled (SEQ ID NO: 160). 
     The ˜1 kb upstream and downstream homology arms were PCR amplified from  C. autoethanogenum  with primers SN22f/SN23r and SN28f/SN29r. Ptb and buk genes were PCR amplified from pIPA_16 plasmid using primers SN24f/SN25r. The ermB cassette with loxP sites was PCR amplified using primers SN26f/SN27r. The plasmid backbone was PCR amplified with primers SN30f/SN31r. KAPA polymerase was used for all PCR amplifications. The PCR products were assembled using GeneArt Seamless cloning kit from Life Technologies and plasmid with no mutations in the insert fragments was used to transform  C. autoethanogenum  by conjugation as described earlier. 
     Following conjugation and selection on trimethoprim and clarithromycin, 7 colonies were streaked twice on PETC-MES agar plates with clarithromycin and anhydrotetracycline to induce the expression of mazF genes. The colonies from clarithromycin and anhydrotetracycline should have the pta and ack genes replaced with ptb and buk genes and ermB cassette. This was verified by PCR using primers Og29f/Og30r flanking the homology arms and KAPA polymerase ( FIG. 25 ). While a band of ˜4.6 kb is amplified from the wildtype strain, bands of ˜5.7 kb was amplified from colonies 1 and 4-7, indicating the replacement of pta and ack genes replaced with ptb and buk genes and ermB cassette. The above event was further confirmed by sequencing the PCR products from clones 4-7. 
     With the resulting modification the expression of ptb and buk genes is driven by the promoter upstream of pta gene. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 SEQ ID NO: 
                 Name 
                 Sequence 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 161 
                 SN22f 
                 TTTACAAATTCGGCCGGCCAAAGATTGCTCTATGTTTAAGCT 
               
               
                   
               
               
                 162 
                 SN23r 
                 CATCAAAGTTTTTACTCATCAATTTCATGTTCATTTCCTCCCT 
               
               
                   
               
               
                 163 
                 SN24f 
                 AGGGAGGAAATGAACATGAAATTGATGAGTAAAAACTTTGAT 
               
               
                   
                   
                 GAGT 
               
               
                   
               
               
                 164 
                 SN25r 
                 GTATAGCATACATTATACGAACGGTACTAGTAAACCTTAGCTT 
               
               
                   
                   
                 GTTCTTC 
               
               
                   
               
               
                 165 
                 SN26f 
                 GAAGAACAAGCTAAGGTTTACTAGTACCGTTCGTATAATGTAT 
               
               
                   
                   
                 GCTATAC 
               
               
                   
               
               
                 166 
                 SN27r 
                 AGAGATGAGCATTAAAAGTCAAGTCTACCGTTCGTATAGCATA 
               
               
                   
                   
                 CA 
               
               
                   
               
               
                 167 
                 SN28f 
                 TGTATGCTATACGAACGGTAGACTTGACTTTTAATGCTCATCTCT 
               
               
                   
               
               
                 168 
                 SN29r 
                 CATGAGATTATCAAAAAGGAGTTTAAATATCTATTTTGTCCTTA 
               
               
                   
                   
                 GGA 
               
               
                   
               
               
                 169 
                 SN30f 
                 TCCTAAGGACAAAATAGATATTTAAACTCCTTTTTGATAATCTC 
               
               
                   
                   
                 ATG 
               
               
                   
               
               
                 170 
                 SN31r 
                 AGCTTAAACATAGAGCAATCTTTGGCCGGCCGAATTTGTAAA 
               
               
                   
               
               
                 171 
                 Og29f 
                 AGCCACATCCAGTAGATTGAACTTT 
               
               
                   
               
               
                 172 
                 Og30r 
                 AATTCGCCCTACGATTAAAGTGGAA 
               
               
                   
               
            
           
         
       
     
     The resulting strain  C. autoethanogenum  pta-ack::ptb-buk, in which the pta-ack operon was replaced by the ptb-buk operon was transformed as described above with the isopropanol production plasmid pMTL85147-thlA-adc from Example 2. A growth study was carried out under autotrophic conditions and analyzed for metabolic end products. No acetate production was observed, while isopropanol (up to 0.355 g/L) and 3-HB (up to 0.29 g/L) was still produced alongside ethanol and 2,3-butanediol ( FIGS. 39A and 39B ). This demonstrates that it is possible to produce isopropanol and 3-HB without acetate production from gaseous substrates CO and/or CO 2  and H 2  using the Ptb-Buk system. 
     If acetone rather than isopropanol is the target product, the primary:secondary alcohol dehydrogenase gene (SEQ ID NO: 17) can be further knocked out this strain  C. autoethanogenum  pta-ack::ptb-buk using methods described above and in detail in WO 2015/085015. Introducing plasmid pMTL85147-thlA-adc into this strain results in production of acetone at similar levels as described above for isopropanol without co-production of acetate. Ethanol, 2,3-butanediol and 3-HB may be further products. 
     By further knock-outs it is possible to eliminate these products as well, e.g., knock-out of the acetolactate decarboxylase gene BudA results in a strain unable to produce 2,3-butanediol (U.S. Pat. No. 9,297,026). 3-HB production may be reduced or eliminated by deletion of 3-hydroxybutyrate dehydrogenase gene Bdh (SEQ ID NO: 62). 
     Example 9 
     This example demonstrates improvement of conversion of 3-hydroxybutyrate to 1,3-BDO by overexpression of the aldehyde:ferredoxin oxidoreductase gene aor1. 
     The pMTL82251 plasmid backbone was used for overexpression of the  C. autoethanogenum  aor1 gene. The pMTL82251 plasmid was selected since it has a different replication origin and antibiotic marker, but could be co-expressed with, the plasmid used in Example 5 that contained hbd1 and thlA. Preparation of the plasmid backbone and the assembly reaction were carried out following the procedures listed above, first generating plasmid pMTL82256 by introducing the  C. autoethanogenum  ferredoxin promoter into plasmid pMTL82251 and then adding the aor1 genes to form plasmid pMTL82256-aor1. The following primers were used. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
                   
               
               
                 NO: 
                 Name 
                 Sequence 
                 Direction 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 173 
                 Pfdx-F1 
                 AAAGGTCTCCGGCCGCGCTCACTATCTGCGGAACC 
                 forward 
               
               
                   
               
               
                 174 
                 Pfdx-R1 
                 TTTGGTCTCGAATTCTGTAACACCTCCTTAATTTT 
                 reverse 
               
               
                   
                   
                 TAG 
               
               
                   
               
               
                 175 
                 aorl-F1 
                 AAAGGTCTCGAATTCAAAGATCTATGTATGGTTA 
                 forward 
               
               
                   
                   
                 TGATGGTAAAGTATTAAG 
               
               
                   
               
               
                 176 
                 aorl-R1 
                 TTTGGTCTCCTCGAGTATGGATCCCTAGAACTTAC 
                 reverse 
               
               
                   
                   
                 CTATATATTCATCTAATCC 
               
               
                   
               
            
           
         
       
     
     After transforming the resulting plasmid pMTL82256-aor1 into the  E. coli  CA434 strain, conjugation was performed on the previous  C. autoethanogenum  1,3-BDO production host. Thus, the resulting  C. autoethanogenum  strain carried two plasmids, one for overexpressing hbd1 and thlA, and another for aor1, under different replication origins and selection marker. The production for 1,3-BDO was characterized and quantified following the procedures above. 
     The results clearly show that 1,3-BDO production can be improved by overexpressing aor1. Likewise other aldehyde:ferredoxin oxidoreductase genes could be expressed in  C. autoethanogenum  to facilitate convserion of 3-hydroxybutyrate to 1,3-butanediol. 
     To improve of 1,3-BDO production, AOR was overexpressed to improve conversion of 3-HB to 3-HB-aldehyde. To do this, pMTL82256-hbd-thlA and pMTL83159-aor1 were coexpressed in  C. autoethanogenum . As compared to the strain that carried pMTL82256-hbd-thlA alone, the aor1-coexpressed strain produced higher ethanol and 1,3-BDO ( FIG. 44 ). 
     Example 10 
     This example demonstrates the stereospecificity of Ptb-Buk that allows for the production of 2-hydroxyisobutyric acid without the production of unwanted byproducts. 
     2-hydroxyisobutyric acid can be produced in  E. coli  and  C. autoethanogenum  by introduction of a thiolase and a 3-hydroxybutyryl-CoA dehydrogenase to convert acetyl-CoA to 3-hydroxybutyryl-CoA, a 2-hydroxyisobutyryl-CoA mutase enzyme for conversion of 3-hydroxybutyryl-CoA to 2-hydroxyisobutyryl-CoA and an enzyme that can hydrolyse the CoA to form 2-hydroxyisobutyric acid. The 3-hydroxybutyryl-CoA dehydrogenase can either be (R)- or (S)-specific and the enzyme converting 2-hydroxyisobutyryl-CoA to 2-hydroxybutyrate according to steps 1, 13, 19, and 20 of  FIG. 1 . This last step can either be done via a thioesterase or the Ptb-Buk system. 
     Three potential candidate genes,  E. coli  thioesterase type II TesB, the  C. autoethanogenum  phosphate acetyltransferase/acetate kinase pair and the  C. beijerinckii  butyryltransferase/butyrate kinase pair were cloned into  E. coli  pDUET T7 expression vectors via methods described above and primers below. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 SEQ ID 
                   
                   
               
               
                 NO: 
                 Primer 
                 Sequence 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 177 
                 pETDuet-pta-ack- 
                 GGGTACCTTATTTATTTTCAACTATTTCTTTTGTATC 
               
               
                   
                 ack-DuetI2-R1 
               
               
                   
               
               
                 178 
                 pETDuet-pta-ack- 
                 TTGAAAATAAATAAGGTACCCTCGAGTCTGGTAAAG 
               
               
                   
                 DuetI2-ack-F1 
               
               
                   
               
               
                 179 
                 pETDuet-pta-ack- 
                 TTTTTTCCATATGTATATCTCCTTCTTATACTTAAC 
               
               
                   
                 DuetI2-pta-R1 
               
               
                   
               
               
                 180 
                 pETDuet-pta-ack- 
                 AGGAGATATACATATGGAAAAAATTTGGAGTAAGGC 
               
               
                   
                 pta-DuetI2-F1 
               
               
                   
               
               
                 181 
                 pETDuet-tesB- 
                 GAAATCATAATTAAGGTACCCTCGAGTCTGGTAAAG 
               
               
                   
                 DuetI2-tesB-F1 
               
               
                   
               
               
                 182 
                 pETDuet-tesB- 
                 CCTGACTCATATGTATATCTCCTTCTTATACTTAAC 
               
               
                   
                 DuetI2-tesB-R1 
               
               
                   
               
               
                 183 
                 pETDuet-tesB-tesB- 
                 AAGAAGGAGATATACATATGAGTCAGGCACTTAAAA 
               
               
                   
                 DuetI2-F1 
               
               
                   
               
               
                 184 
                 pETDuet-tesB- 
                 AGGGTACCTTAATTATGATTTCTCATAACACCTTC 
               
               
                   
                 testB-DuetI2-R1 
               
               
                   
               
            
           
         
       
     
     The obtained plasmids pDUET-pta-ack (SEQ ID NO: 185), pDUET-ptb-buk (SEQ ID NO: 186), pDUET-tesB (SEQ ID NO: 187) and introduced into  E. coli  BL21 (DE3) for expression and then assayed for their activity on acetoacetyl-CoA, 3-hydroxybutyryl-CoA and 2-hydroxyisobutyryl-CoA. The results are shown in  FIG. 27 .  E. coli  BL21 has a small but measurable amount of activity on all three substrates. Pta-Ack resulted in no activity above background, while both thioesterase TesB and Ptb-Buk showed high activity on all three substrates, including 2-hydroxyisobutyryl-CoA. 
     The activity of both thioesterase TesB and Ptb-Buk was higher on linear acetoacetyl-CoA, 3-hydroxybutyryl-CoA than on branched 2-hydroxyisobutyryl-CoA. This creates a problem in the pathway as it results in early termination of the pathway at 3-hydroxybutyryl-CoA, in particular as activities are higher than activities on the 2-hydroxyisobutyryl-CoA mutase enzyme. 
     However, Ptb-Buk in contrast to thioesterases is able to distinguish between stereoisomers and will only (or preferentially) act on (R)-3-hydroxybutyryl-CoA but not on (S)-3-hydroxybutyryl-CoA. This was demonstrated by expressing the Ptb-Buk system either with ThlA and (S)-specific Hbd ( FIG. 28A ) or (R)-specific phaB ( FIG. 28B ) in the pDuet system in  E. coli . The constructs were constructed as described in Examples 1 and 3. Growth studies confirmed that appreciable amounts of 3-hydroxybutyrate were only formed when Ptb-Buk was expressed in combination with the (S)-specific Hbd but not the (R)-specific phaB. 
     Therefore, a route via an (S)-specific 3-hydroxybutyryl-CoA dehydrogenase and the Ptb-Buk provides significant advantages, as the Ptb-Buk system (unlike thioesterases) is not active on (S)-3-hydroxybutyryl-CoA but (S)-3-hydroxybutyryl-CoA is also the preferred isomer of the 2-hydroxyisobutyryl-CoA mutase (Yaneva,  J Biol Chem,  287: 15502-15511, 2012). The produced 2-hydroxyisobutyryl-CoA can then be used via the Ptb-Buk to produce 2-hydroxyisobutyric acid and (unlike thioesterases) 2-hydroxyisobutyryl-CoA hydrolysis provides additional energy ( FIG. 8 ). 
     Modular constructs were designed to compare performance of the pathway. A gene cassette containing the Wood-Ljungdahl promoter in front of the genes meaB, hcmA and hcmB was codon optimized and synthesized (SEQ ID NO: 188). HcmA and hcmB encode a 2-hydroxyisobutyryl-CoA mutase and meaB a chaperon from  Aquincola tertiaricarbonis , in the construct hcmA and meaB genes were fused together as one protein as described (SEQ ID NO: 189) (Yaneva,  J Biol Chem,  287: 15502-15511, 2012). The gene cassette was cloned into either a plasmid containing thiolase (thlA from  C. acetobutylicum ; SEQ ID NO: 136) and an (S)-specific 3-hydroxybutyrate dehydrogenase (hbd from  C. acetobutylicum ; SEQ ID NO: 190) (pMTL83155-thlA-hbd) or an (R)-specific 3-hydroxybutyrate dehydrogenase (phaB from  R. eutropha ) (pMTL83155-thlA-phaB) using the restriction enzymes KpnI and NcoI to form plasmids pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB (SEQ ID NO: 191) and pMTL83155-thlA-phaB-Pwl-meaBhcmA-hcmB (SEQ ID NO: 192), respectively. Sub-cloning of the codon optimized 2-hydroxyisobutyryl-CoA mutase casette in  E. coli  Top-10 was only successful after some initial cloning complications; it was found that the 2-hydroxyisobutyryl-CoA mutase casette could only be cloned into the plasmid at a lower temperature (28° C.). 
     Vector pMTL83155-thlA-hbd and pMTL83155-thlA-phaB were created by first amplifying a promoter region of the phosphate acetyltransferase of  C. autoethanogenum  (SEQ ID NO: 193) and cloning into vector pMTL83151 (FJ797647.1; Heap,  J Microbiol Meth,  78: 79-85, 2009) using NotI and NdeI restriction sites before introducing genes thlA and hbd or respectively phaB via NdeI and KpnI in a double ligation reaction. 
     In addition, compatible plasmid modules for expressing ptb-buk or tesB were built. For this, the respective genes were amplified from genomic DNA and introduced into plasmid pMTL82256 described in Example 9 and then introducing either ptb-buk or phaB using NdeI and NcoI and Seamless Cloning kit (Life technologies) to form plasmids pMTL82256-ptb-buk (SEQ ID NO: 194) and pMTL82256-tesB (SEQ ID NO: 195). 
     Plasmids pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB, pMTL83155-thlA-phaB-Pwl-meaBhcmA-hcmB, pMTL82256-ptb-buk and pMTL82256-tesB were introduced into  E. coli  Top-10 (all steps at 28° C.) and  C. autoethanogenum  by transformation as described in previous examples in the following combinations: pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk, pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-tesB, pMTL83155-thlA-phaB-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk and pMTL83155-thlA-phaB-Pwl-meaBhcmA-hcmB+pMTL82256-tesB. 
     Growth experiments were carried out with  E. coli  in LB medium at 30° C. for 4 days and  C. autoethanogenum  in PETC medium with 30 psi CO-containing steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ) at 30° C. and 37° C. for 6 days. Metabolites were measured as described above. In addition to measurement by GC-MS, 2-Hydroxyisobutyric acid production was also confirmed using liquid chromatography tandem mass spectrometry (LC-MS/MS) and  1 H nuclear magnetic resonance (NMR) spectroscopy. 
     Liquid chromatography tandem mass spectrometry (LC-MS/MS) data was acquired on a Dionex UltiMate 3000 liquid chromatography system (Dionex, Calif., USA) coupled to an ABSciex 4000 QTRAP mass spectrometer (ABSciex, Concord, Canada). The liquid chromatography system was controlled by Chromeleon software (Dionex), and chromatographic separation was achieved by injecting 104 onto a Gemini-NX C18 150 mm×2 mm I.D., 3 μm 110 Å particle column (Phenomenex, Aschaffenburg, Germany) equipped with a pre-column Security Guard Gemini-NX C18 4 mm×2 mm I.D. cartridge. The column oven temperature was controlled and maintained at 55° C. throughout the acquisition and the mobile phases were as follows: 7.5 mM aqueous tributylamine adjusted to pH 4.95 (±0.05) with glacial acetic acid (eluent A) and acetonitrile (eluent B). The mobile phase flow rate was maintained at 300 μL/min throughout a gradient profile and was introduced directly into the mass spectrometer with no split. The mass spectrometer was controlled by Analyst 1.5.2 software (ABSciex) and was equipped with a TurboV electrospray source operated in negative ionisation mode. The following previously optimized (and therefore general) parameters were used to acquire scheduled Multiple Reaction Monitoring (MRM) data: ionspray voltage −4500V, nebulizer (GS1), auxiliary (GS2), curtain (CUR) and collision (CAD) gases were 60, 60, 20 and medium (arbitrary units), respectively, generated via a N300DR nitrogen generator (Peak Scientific, Massachusetts, USA). The auxiliary gas temperature was maintained at 350° C. The entrance potential (EP) was −10 volts. This method is also able to detect and separate 2-hydroxybutyric acid. 
       1 H nuclear magnetic resonance (NMR) spectroscopy at a field strength of 400 MHz. Samples were prepared by diluting 400 μL of sample with 400 μL of 20 mM phosphate buffer prepared with D 2 O and containing trimethylsilyl proprionic acid (TMSP) as internal standard (pH of 7). The samples were then transferred glass NMR tube (5 mm×8 inches) and analysed by  1 H NMR using presaturation for water suppression with a 30° excitation pulse, 15 second relaxation delay and 64 scans at a temperature of 27° C. Once acquired the spectrum was transformed, flattened and integrated using Agilent VnmrJ software. The known concentration of TMSP was used for quantitation of 2-hydroxyisobutyric using the resonance at 1.36 ppm (singlet). 
     In both  E. coli  growing heterotrophically as well as  C. autoethanogenum  growing autotrophically, 2-hydroxyisobutyric acid could be detected in constructs pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-tesB (1.5 mg/L in LC-MS/MS method and 8 mg/L in GC-MS in  C. autoethanogenum;  0.5 mg/L in LC-MS/MS method and 2 mg/L in GC-MS in  E. coli ) and pMTL83155-thlA-phaB-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk (15 mg/L in LC-MS/MS method and 75 mg/L in GC-MS in  C. autoethanogenum;  1.1 mg/L in LC-MS/MS method and 8.5 mg/L in GC-MS in  E. coli ), but not in constructs all other constructs including the control. By far the highest production occurred in strain carrying plasmid pMTL83155-thlA-hbd-Pwl-meaBhcmA-hcmB+pMTL82256-ptb-buk (10× higher than all other routes), that has the optimal pathway with thiolase, (S)-specific (S)-specific 3-hydroxybutyryl-CoA dehydrogenase, the 2-hydroxyisobutyryl-CoA mutase, and the Ptb-Buk system ( FIGS. 29A-D ). Surprisingly, also production of 2-hydroxybutyrate (2-HB) (up to 64 mg/L by LC-MS/MS and 50 mg/L by GC-MS in  C. autoethanogenum;  12 mg/L by LC-MS/MS and 9.5 mg/L by GC-MS in  E. coli ) was found in this strain, indicating unspecific mutase activity ( FIG. 30 ). This was also found in the tesB strain, but again at significant lower levels (18 mg/L in LC-MS-MS and 9 mg/L in GC-MS in  C. autoethanogenum ). Production of 2-hydroxyisobutyric acid was also confirmed by NMR. 
     In addition, also qRT-PCR was carried out to confirm expression of the genes thlA, hbd, meaBhcmA and hcmB ( FIG. 31 ). 
     The RT-PCR graphs show that thlA gene product is expressed to slightly higher levels with the P pta-ack  promoter than hbd (as expected with a second gene in an operon) and that hmcB shows slightly lower expression levels than meaBhcmA. Also there is lower expression in  C. autoethanogenum  at 30° C. than at 37° C. and  E. coli  at 30° C. For specific cycle numbers see below. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Condition 
                 Target 
                 Cq Mean 
                 Cq Std Dev 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   E. coli /30° C. 
                 thlA 
                 18.26 
                 0.243 
               
               
                   
                 hbd 
                 20.6 
                 0.603 
               
               
                   
                 meaBhcmA 
                 16.20 
                 0.108 
               
               
                   
                 hmcB 
                 18.30 
                 0.666 
               
               
                   C. autoethanogenum /30° C. 
                 thlA 
                 26.10 
                 0.169 
               
               
                   
                 Hbd 
                 27.54 
                 0.415 
               
               
                   
                 meaBhcmA 
                 20.63 
                 0.604 
               
               
                   
                 hmcB 
                 22.64 
                 0.697 
               
               
                   C. autoethanogenum /37° C. 
                 thlA 
                 18.48 
                 0.069 
               
               
                   
                 hbd 
                 21.85 
                 0.222 
               
               
                   
                 meaBhcmA 
                 16.72 
                 0.119 
               
               
                   
                 hmcB 
                 19.62 
                 0.173 
               
               
                   
               
            
           
         
       
     
     The ratio of (S)-3-hydroxybutyric acid to (R)-3-hydroxybutyric acid was measured by high-performance liquid chromatography (HPLC) on an Agilent 1260 Infinity LC with UV detection at 210 nm. Samples were prepared by centrifugation at 14,000 rpm for 3 minutes, followed by evaporation of 200 μL of supernatant to dryness. The pellet was then re-suspended in 100% Isopropanol and sonicated under heat for 1 hour. Centrifugation was repeated and the supernatant transferred to an HPLC vial for analysis. Separation was achieved with a 5 μL injection on to a TCI Chiral MB-S column (250 mm×4.6 mm×3 μm) at 1.5 mL/min and 40° C. under isocratic conditions, using 95-5 hexane-isopropanol mobile phase containing 0.1% trifluoracetic acid. 
     A stereospecific analysis of produce 3-HB has been performed. Surprisingly it was found that in  C. autoethanogenum , a mix of isomers was produced. Enzymes Hbd and PhaB are described to be stereospecific, PhaB is R-specific and Hbd is S-specific and when expressing these enzymes in  E. coli  a stereopure product has been observed (Tseng,  Appl Environ Microbiol,  75: 3137-3145, 2009). 
     The following table indicates the distribution of (R)- and (S)-form of 3-HB at equilibrium produced via three different routes in  C. autoethanogenum . These data suggest the presence of isomerase in the  C. autoethanogenum . 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                 Route 
                 % R-form 
                 % S-form 
               
               
                   
               
             
            
               
                   
                 ThlA-PhaB 
                 55 ± 7 
                 53 ± 5 
               
               
                   
                 ThlA-HBD 
                 12 ± 3 
                 88 ± 3 
               
               
                   
                 ThlA-ctfAB 
                 16 ± 7 
                 84 ± 7 
               
               
                   
               
            
           
         
       
     
     Knockout of native isomerases may prevent interconversion of (R) and (S) forms of 3-HB. Alternatively, expression or overexpression of isomerases could enable new ptb-buk routes. For example, Hbd could be used to generate (S)-3-HB, isomerase could convert (S)-3-HB to (R)-3-HB, and ptb-buk could act on (R)-3-HB to produce products of interest. 
     Example 11 
     This example demonstrates the production of isobutylene via Ptb-Buk conversion of 3-hydroxyisovaleryl-CoA and 3-hydroxyisovalerate. 
     Different routes for production of isobutylene have been described, for example the conversion of acetone to isobutylene via a hydroxyisovalerate synthase and decarboxylase (van Leeuwen,  Appl Microbiol Biotechnol,  93: 1377-1387, 2012). However, the hydroxyisovalerate decarboxylase step is an ATP requiring step and kinetics of this enzyme may not be ideal. Two alternative routes to isobutylene using the Ptb-Buk system have been identified through 3-hydroxyisovaleryl-CoA which has been shown in vitro to be a viable substrate for the Ptb-Buk system (Liu,  Appl Microbiol Biotechnol,  53: 545-552, 2000). 
     Alternative pathway 1 consists of a synthase that converts acetone into 3-hydroxyisovaleryl-CoA ( FIG. 9 ). 
     Alternative pathway 2 proceeds via known intermediate 3-methyl-2-oxopentanoate of the isoleucine biosynthesis that is common to bacteria such as  E. coli  or  C. autoethanogenum  ( FIG. 10 ). 
     Example 12 
     This example describes methods for characterizing Ptb-Buk variants. 
     Given the substrate promiscuity of Ptb-Buk, it is likely that Ptb-Buk systems of varying amino acid sequences will possess varying preferences for given substrates. In order to identify a Ptb-Buk system that favors a desired substrate (e.g. acetoacetyl-CoA, 3-hydroxybutyryl-CoA, 2-hydroxyisobutyryl-CoA, acetyl-CoA, and/or butyryl-CoA), a high-throughput screen is desirable. Such a screen can be accomplished by coupling firefly luciferase (Luc) to the Ptb-Buk system ( FIG. 33 ). Luc reacts with D-luciferin, generating oxyluciferin, carbon dioxide, and light. In addition to magnesium and molecular oxygen, Luc requires ATP for the reaction to proceed. ATP is a product generated by Ptb-Buk when provided an appropriate acyl-CoA or enoyl-CoA substrate. Therefore, Ptb-Buk reaction rates and preferences can be compared for varying substrates by quantifying the amount of light generated by a reaction containing Ptb-Buk, Luc, d-luciferin, magnesium, molecular oxygen, phosphate, ADP, and an acyl-CoA or enoyl-CoA. 
     Example 13 
     This example uses genome-scale modeling to demonstrate that high non-native product selectivities can be achieved using Ptb-Buk. Furthermore, it shows that the use of Ptb-Buk could permit the coupling of cellular growth with product production, allowing the construction of stable and high-yielding fermentation strains. 
     A genome-scale metabolic model of  C. autoethanogenum  similar to the one described by Marcellin,  Green Chem,  18: 3020-3028, 2006 was utilized. Variants of this model were created that incorporate additional metabolic reactions, each one representing a different genetically modified microorganism for non-native product formation. Three model versions were created for each non-native product pathway, incorporating either a thioesterase, acetate CoA-transferase or Ptb-Buk reaction. 
     Maximum selectivities were calculated using flux balance analysis (FBA), using scripts from the COBRA Toolbox v2.0 in MATLAB R2014a (The Mathworks, Inc.) with Gurobi version 6.0.4 as the solver (Gurobi Optimization, Inc.). Exchange reactions were constrained to represent a chemically defined minimal growth medium with CO as the source of carbon and energy. An evolutionary algorithm was used to search for the existence of strain designs incorporating up to ten gene knockouts that couple target non-native chemical production with growth. 
     FBA predicts that pathways using Ptb-Buk or CoA transferase offer the highest product selectivities due to ATP gain through substrate level phosphorylation. The results are illustrated in Table 2. However, it should be noted that one limitation of Genome-scale models and FBA analysis is that enzyme kinetics are not captured. The CoA transferase reaction requires a certain base level of acetate for functionality, therefore in reality the maximum selectivity using a CoA transferase would be less than 100% due to a base level of acetate required to be present. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Flux balance analysis (FBA) showing the maximum possible 
               
               
                 non-native product selectivities in  C. autoethanogenum   
               
               
                 for a set of products and candidate enzymes. 
               
            
           
           
               
               
            
               
                   
                 Maximum selectivity % (C in target product/ 
               
               
                   
                 C in all fermentation products) 
               
            
           
           
               
               
               
               
            
               
                 Non-native product 
                 Thioesterase 
                 CoA-transferase 
                 Ptb-Buk 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Acetone 
                 82.0 
                 100 
                 100 
               
               
                 Isopropanol 
                 82.1 
                 100 
                 100 
               
               
                 Isobutylene 
                 55.9 
                 80.2 
                 80.2 
               
               
                 3-Hydroxybutyrate 
                 86.0 
                 100 
                 100 
               
               
                 1,3-Butanediol 
                 88.6 
                 100 
                 100 
               
               
                 2-Hydroxyisobutyrate 
                 86.0 
                 100 
                 100 
               
               
                   
               
            
           
         
       
     
     It is desirable to construct strains where the target non-native chemical must be produced for cell growth. FBA predicts that in most cases it would be difficult to couple target chemical production with growth when using a thioesterase or a CoA transferase; instead, native products acetate and ethanol would be favored. However, when using Ptb-Buk, many growth-coupled chemical production strain designs exist, often incorporating a disruption of the phosphotransacetylase-acetate kinase reactions. Table 3 summarizes the growth coupling ability of each strain. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Potential to couple non-native chemical production with 
               
               
                 growth in  C. autoethanogenum  during growth on CO when 
               
               
                 reconfiguring the metabolic network with up to ten 
               
               
                 gene knockouts. 
               
            
           
           
               
               
            
               
                   
                 Ability to couple non-native chemical 
               
               
                   
                 production with growth 
               
            
           
           
               
               
               
               
            
               
                 Non-native product 
                 Thioesterase 
                 CoA-transferase 
                 Ptb-Buk 
               
               
                   
               
               
                 Acetone 
                 No 
                 No 
                 Yes 
               
               
                 Isopropanol 
                 No 
                 No 
                 Yes 
               
               
                 Isobutylene 
                 No 
                 No 
                 No 
               
               
                 3-Hydroxybutyrate 
                 No 
                 No 
                 Yes 
               
               
                 1,3-Butanediol 
                 No 
                 Yes 
                 Yes 
               
               
                 2-Hydroxyisobutyrate 
                 No 
                 No 
                 Yes 
               
               
                   
               
            
           
         
       
     
     While both Ptb-Buk and CoA transferase can support high selectivities, flux balance analysis predicts that in most cases, only Ptb-Buk would allow the construction of stable, high-yielding fermentation strains that couple non-native chemical production with growth. 
     Example 14 
     This example demonstrates the production of adipic acid via Ptb-Buk from gaseous feedstock. 
     Production of adipic acid in  E. coli  from sugar has been described by a pathway utilizing Ptb-Buk (Yu,  Biotechnol Bioeng,  111: 2580-2586, 2014). However production was low, in the μg/L range. Without wishing to be bound by any particular theory, the inventors believe that this is likely a function of lacking driving force in forms of reducing power and surplus ATP. Using a reduced gaseous substrate as CO and H 2  and an acetogenic bacterium such as  C. autoethanogenum , this current limitation can be overcome. CO and H 2  oxidation provide sufficient driving force for reduction of 3-oxo-adipyl-CoA to 3-hydroxyadipyl-CoA by 3-hydroxybutyryl-CoA dehydrogenase or acetoacetyl-CoA hydratase and 2,3-dehydroadipyl-CoA to adipyl-CoA by enoyl-CoA hydrolase or enoyl-CoA reductase ( FIG. 34 , steps 23 and 25), in contrast to  E. coli  growing heterotrophically on more oxidized sugars. Acetogenic bacteria live on the energetic limit of life and therefore ATP generating reactions like the Ptb-Buk system have a strong driving force, ensuring efficient conversion of adipyl-CoA to adipic acid ( FIG. 34 , step 26), in contrast to  E. coli  growing heterotrophically on sugars generating surplus ATP from glycolysis. 
     To produce adipic acid from gas in  C. autoethanogenum , genes encoding a succinyl-CoA synthetase from  E. coli  (NP_415256, NP_415257), a ketoisovalerate oxidoreductase PaaJ from  E. coli  (WP_001206190.1), a 3-hydroxybutyryl-CoA dehydrogenase Hbd from  Clostridium beijerinckii  (WP_011967675.1), a trans-2-enoyl-CoA reductase Crt from  C. acetobutylicum  (NP_349318.1), trans-2-enoyl-CoA reductase Bcd from  C. acetobutylicum  (NP_349317.1) and electron flavoproteins EtfAB (NP_349315, NP_349316) are cloned on an expression plasmid and then transformed as described above in  C. autoethanogenum  strains pta-ack::ptb-buk or CAETHG_1524::ptb-buk from previous examples. Adipic acid is produce according to the steps depicted in  FIG. 34 . 
     Example 15 
     This example demonstrates the production of various products including 2-buten-1-ol, 3-methyl-2-butanol, 1,3-hexanediol (HDO) via Ptb-Buk and AOR. 
     As demonstrated in Example 6, Ptb-Buk is highly promiscuous and acts on a wide range of CoAs as substrates or can be engineered to use a range of non-natural CoAs as substrates. Likewise AOR enzyme has been shown to act on a wide range of substrates. Together these two enzymes can convert a wide range of CoAs via their acids into aldehydes, which then can be further converted to alcohols, ketones or enols via alcohol dehdydrogeneses, for which a wide variety exists in nature. While under standard conditions the reduction of acids with ferredoxin to aldehydes via the AOR is endergonic (Thauer,  Bacteriol Rev,  41: 100-180, 1977) and as such not feasible, it surprisingly is in carboxydotrophic acetogens such as  C. autoethanogenum  that operate at low pH and with CO or H 2  as substrate (Mock,  J Bacteriol,  197: 2965-2980, 2015). One common limitation working with acetogens is that they are ATP-limited, living on the thermodynamic edge of life (Schuchmann,  Nat Rev Microbiol,  12: 809-821, 2014), which can be overcome by coupling this acid reduction to ATP-linked formation of acids from CoAs via the Ptb-Buk system. 
     The Ptb-Buk system and AOR system has been demonstrated in above examples for several different products, but can be extended to further products, for example production of 2-buten-1-ol, 3-methyl-2-butanol, 1,3-hexanediol (HDO). 2-Buten-1-ol can be produced via Ptb-Buk, AOR and an alcohol dehydrogenase from crotonyl-CoA ( FIG. 35 ). 1,3-Hexanediol can be produced via Ptb-Buk, AOR and an alcohol dehydrogenase from 3-hydroxy-hexanoyl-CoA ( FIG. 35 ). By combining Ptb-Buk, Adc and an alcohol dehydrogenase (such as native primary: secondary alcohol dehydrogenase), 3-methyl-2-butanol can be formed from acetobutyryl-CoA. 
     All of these precursors, crotonyl-CoA, 3-hydroxy-hexanoyl-CoA, or acetobutyryl-CoA can be formed by reduction and elongation of acetyl-CoA, acetoacetyl-CoA and 3-HB-CoA which are described in previous examples via known fermentation pathways of, for example,  Clostridium kluyveri  (Barker,  PNAS USA,  31: 373-381, 1945; Seedorf,  PNAS USA,  105: 2128-2133, 2008) and other  Clostridia . Involved enzymes include crotonyl-CoA hydratase (crotonase) or crotonyl-CoA reductase, butyryl-CoA dehydrogenase or trans-2-enoyl-CoA reductase, thiolase or acyl-CoA acetyltransferase and 3-hydroxybutyryl-CoA dehydrogenase or acetoacetyl-CoA hydratase ( FIG. 35 ). Respective genes from  C. kluyveri  or other  Clostridia  have be cloned on an expression plasmid (U.S. 2011/0236941) and then transformed as described above in  C. autoethanogenum  strains pta-ack::ptb-buk or CAETHG_1524::ptb-buk from previous examples for production of 2-buten-1-ol, 3-methyl-2-butanol, 1,3-hexanediol (HDO). 2-Buten-1-ol, 3-methyl-2-butanol, and 1,3-hexanediol (HDO) may be precursors for further downstream products. 
     While these are only a few examples, it should be clear that this pathway can be further extended using the same enzymes or engineered variants thereof that have specificity for higher chain length to produce a range of C4, C6, C8, C10, C12, C14 alcohols, ketones, enols or diols ( FIG. 39 ). Different type of molecules can be obtained also by using primer or extender units different than acetyl-CoA in the thiolase step as been described elsewhere (Cheong,  Nature Biotechnol,  34: 556-561, 2016). 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement that that prior art forms part of the common general knowledge in the field of endeavour in any country. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.