Abstract:
Novel methods for the in vivo production of phenol from renewable substrates using a recombinant microorganism (FIG.  1 ). Additionally, methods for the in vivo production of catechol and cis,cis-muconic acid from renewable substrates using a recombinant microorganism are disclosed. A host cell expresses at least one gene encoding a polypeptide that possesses isochorismate synthase activity, at least one gene encoding a polypeptide that possesses isochorismate pyruvate lyase activity, and at least one gene encoding a polypeptide that possesses salicylic acid decarboxylase activity. In the case of catechol, the host cell must additionally express at least one gene encoding a polypeptide that possesses phenol 2-monooxy-genase activity. In the case of cis,cis-muconic acid, the host cell must additionally express at least one gene encoding a polypeptide that possesses phenol 2-monooxygenase activity and at least one gene encoding a polypeptide that possesses catechol-1,2-dioxygenase activity.

Description:
CROSS REFERENCE 
       [0001]    This application claims priority to U.S. provisional patent application 61/870,663 filed on Aug. 27, 2013, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure relates to the fields of molecular biology, microbiology, and biotechnology. More specifically, the present disclosure relates to methods of producing phenol, catechol, and cis,cis-muconic acid from simple renewable substrates, such as glucose, in recombinant microorganisms. 
       BACKGROUND OF THE INVENTION 
       [0003]    Phenol is a useful and versatile chemical used for the production of numerous fine and commodity chemicals. Major products of note include bisphenol A (BPA), caprolactam and salicylic acid. For example, in 2007, BPA production accounted for 44% of global phenol consumption and demand. Phenol is also commonly used in the production of numerous polymers, specifically phenolic resins, polycarbonate, and polyamides. Global phenol demand has increased steadily in the last decade. For instance, global phenol demand, which was 6 million tons in 2000, rose to nearly 8 million tons by 2010. Growth has been strongest in the Asia-Pacific region, which is expected to account for &gt;50% of global phenol demand by 2020, by which point is expected to surpass 11.5 million tons. Phenol is typically derived from petrochemical feedstocks including benzene, toluene, and propylene, and as such its market price is tightly correlated with that of crude oil. Presently, an inexpensive and sustainable source of phenol has not yet been developed. 
       SUMMARY OF THE INVENTION 
       [0004]    The embodiments disclosed herein include an in vivo method for the production of phenol via a recombinant host cell co-expressing at least one gene encoding a polypeptide having isochorismate synthase (ICS) activity to convert endogenous chorismate to isochorismate, at least one gene encoding a polypeptide having isochorismate pyruvate lyase (IPL) activity to then subsequently convert isochorismate to salicylates, and at least one gene encoding a polypeptide having salicylate decarboxylase (SDC) activity to convert salicylate to phenol. 
         [0005]    The embodiments disclosed herein also include an in vivo method for the production of catechol by further engineering said recombinant host cell to co-express at least one gene encoding a polypeptide that displays phenol 2-monooxygenase (PMO) activity. Further embodiments involve an in vivo method for the production of cis,cis-muconate by further engineering said recombinant host cell to co-express at least one gene encoding a polypeptide that displays catechol-1,2-dioxygenase (CDO) activity. The reaction schemes are illustrated in  FIG. 1 . These embodiments provide an inexpensive and sustainable biological route for the conversion of renewable substrates to phenol, catechol, and cis,cis-muconate. All three products are useful, for example, for the synthesis of numerous chemical and polymer products. 
         [0006]    These and other aspects of the invention will be apparent upon reference to the following detailed description and figures. To that end, any patent and other documents cited herein are hereby incorporated by reference in their entirety. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]      FIG. 1  depicts an enzymatic pathway to convert the endogenous precursor chorismate to the product phenol via the intermediates isochorismate and salicylate. The three-step pathway from chorismate is achieved by the co-expression of one or more genes encoding polypeptides with the following activities: isochorismate synthase (ICS; A), isochorismate pyruvate lyase (IPL; B), and salicylate decarboxylase (SDC; C). The additional co-expression of one or more genes encoding phenol 2-monooxygnease (PMO; D) results in the production of catechol. The additional co-expression of one or more genes encoding catechol-1,2-dioxygenase (CDO; E) results in the production of cis,cis-muconate. 
           [0008]      FIG. 2  depicts phenol production from salicylate by  E. coli  BW25113(DE3) pTrcCOLAK-sdc_syn. 50 ml cultures were grown for overnight (induced with 0.2 mM IPTG after 6 hours), pelleted, and then resuspended in 10 ml PBS buffer supplemented with 400 mg/L salicylate. Phenol accumulation in the extracellular medium over a 24 hour period is shown. 
           [0009]      FIG. 3  shows conversion of glucose to phenol in shake flask cultures by (1)  E. coli  NST74 pTrc99A-menF-pchB pTrcCOLAK-sdc_syn, (2)  E. coli  NST74 pTrc99A-entC-pchB pTrcCOLAK-sdc_syn and (3)  E. coli  NST74 ΔpheAΔtyrA pTrc99A-IcsI-pchB pTrcCOLAK-sdc_syn over a 72 hour period. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0010]    The following abbreviations and definitions will be used for the interpretation and specification of the claims: 
         [0011]    “isochorismate synthase” is abbreviated ICS. 
         [0012]    “isochorismate pyruvate lyase” is abbreviated IPL. 
         [0013]    “salicylate decarboxylase” is abbreviated SDC. 
         [0014]    “phenol 2-monooxygenase” is abbreviated PMO. 
         [0015]    “catechol-1,2-dioxygenase” is abbreviated CDO. 
         [0016]    As used herein, the terms “L-phenylalanine”, and “phenylalanine” are used interchangeably. 
         [0017]    As used herein, the terms “cis,cis-muconic acid”, “muconic acid”, cis,cis-muconate”, and “muconate” are used interchangeably. 
         [0018]    As used herein, the terms “chorismic acid” and “chorismate” are used interchangeably. 
         [0019]    As used herein, the terms “isochorismic acid” and “isochorismate” are used interchangeably. 
         [0020]    As used herein, the terms “salicylic acid” and “salicylate” are used interchangeably. 
         [0021]    As used herein, the terms “pyruvic acid” and “pyruvate” are used interchangeably. 
         [0022]    As used herein, the terms “phenol 2-monoxygenase”, and “phenol hydroxylase” are used interchangeably. 
         [0023]    The term “ICS activity” refers to the ability of a protein to catalyze the direct conversion of chorismate to isochorismate. 
         [0024]    The term “IPL activity” refers to the ability of a protein to catalyze the direct conversion of isochorismate to salicylate. 
         [0025]    The term “SDC activity” refers to the ability of a protein to catalyze the direct conversion of salicylate to phenol. 
         [0026]    The term “PMO activity” refers to the ability of a protein to catalyze the direct conversion of phenol to catechol. 
         [0027]    The term “CDO activity” refers to the ability of a protein to catalyze the direct conversion of catechol to cis,cis-muconate. 
         [0028]    The term “chorismate over-producing strain” refers to a microbial strain that produces endogenous levels of chorismate that are significantly higher than those demonstrated by the wild-type of that strain. Specific examples of an  E. coli  chorismate over-producing strains are NST74 and NST37 (U.S. Pat. No. 4,681,852). Meanwhile, still others may include specific strains of  Corynebacterium glutamicum   16 . 
         [0029]    The term “fermentable carbon substrate” refers to a carbon source capable of being metabolized by the host organisms of the present invention and particularly carbon sources selected from the group consisting of monosaccharides, oligosaccharides, polysaccharides, organic acids, glycerol, and one-carbon substrates or mixtures thereof. 
         [0030]    The term “host” refers to a suitable cell line such as a strain of bacteria, for example, into which genes can be transferred to impart desired genetic attributes and functions. 
         [0031]    The term “OD 600 ” refers to the measurement of optical density at 600 nm, a standard metric of cell growth used by those familiar in the art. 
         [0032]    The term “gene” refers to a nucleic acid fragment that expresses a specific protein, including regulatory sequences preceding (5′ non-coding sequences) and following (3′ non-coding sequences) and the coding sequence. “Native gene” or “wild type gene” refers to a gene as found in nature with its own regulatory sequences. “Endogenous gene” refers to a native gene in its natural location in the genome of an organism. “Foreign gene” refers to a gene not normally found in the host organism but that is introduced into the host organism by gene transfer. Foreign genes can comprise native genes inserted into a non-native organism, or chimeric genes. 
         [0033]    The term “expression”, as used herein, refers to the transcription and stable accumulation of sense (mRNA) or antisense RNA derived from the nucleic acid fragment used in this invention. Expression may also refer to the translation of the mRNA into a polypeptide. “Overexpession” refers to the production of a gene product in a transgenic organism that exceeds levels of production in the wild-type host or native organisms. 
         [0034]    “RNA transcript” refers to the product resulting from RNA polymerase-catalyzed transcription of gene or other a DNA sequence. “Messenger RNA (mRNA)” refers to the RNA that is without introns and can be translated into a protein by the cell. “cDNA” refers to double-stranded DNA that is complimentary to and derived from mRNA. “Sense” RNA refers to RNA transcript that includes the mRNA and so can be translated into protein by the cell. 
         [0035]    “Transformation” refers to the transfer of a nucleic acid fragment into the genome genome of the host organism, resulting in genetically-stable inheritance. Host organisms containing the transformed nucleic acid fragments are referred to as “transgenic” or “recombinant” or “transformed” organisms. 
         [0036]    The terms “plasmid” and “vector” refer to an extra chromosomal genetic element often carrying genes which are not part of host native genome nor the central metabolism of the cell, and usually in the form of circular double-stranded DNA molecules. Such elements may be autonomously replicating sequences, genome integrating sequences, phage or nucleotide sequences, linear or circular, of a single- or double-stranded DNA or RNA, derived from any source, in which a number of nucleotide sequences have been joined or recombined into a unique construction which is capable of introducing a promoter fragment and DNA sequence for a selected gene product along with appropriate 3′ untranslated sequence into a cell. 
         [0037]    It would be an advancement in the current state of the art to provide a method by which phenol could be produced from inexpensive and sustainable resources such as carbohydrates or sugars. It would be particularly advantageous if the method produced a high level of phenol at high substrate yields and with a limited diversity and quantity of by-products. The development of such a method requires the ability to manipulate and assemble the appropriate genetic machinery responsible for the conversion of carbohydrates, such as glucose, to chorismate, chorismate to isochorismate, isochorismate to salicylate, and salicylate to phenol. It would be exceptionally advantageous if these conversions could all be achieved within a single host cell. 
         [0038]    Efficient biological production of phenol is difficult. Therefore, the problem to be overcome is to design and develop a method for the efficient production of phenol by a biological source using inexpensive substrates as the carbon source. The applicants have solved the stated problem by engineering a microbial host to produce phenol by expression of foreign genes encoding each of isochorismate synthase (ICS), isochorismate pyruvate lyase (IPL), and salicylate decarboxylase (SDC). 
         [0039]    Furthermore, catechol may be produced by the enzymatic oxidation of phenol by the additional co-expression of one or more genes encoding a polypeptide with phenol 2-monooxygenase (PMO) activity. Further, cis,cis-muconate may be produced by the enzymatic ring-opening oxidation of catechol by the additional co-expression of one or more genes encoding a polypeptide with catechol-1,2-dioxygenase (CDO) activity. cis,cis-Muconate is a platform molecule useful for the synthesis of many plastics precursors. 
       Genes 
       [0040]    The key enzymatic activities used in the present embodiments are encoded by a number of genes known in the art. The principal enzyme activities include isochorismate synthase (ICS), isochorismate pyruvate lyase (IPL), salicylate decarboxylase (SDC), phenol 2-monooxygenase (PMO), and catechol-1,2-dioxygenase (CDO). These activities may also be displayed by enzymes whose principal natural substrates are not chorismate, isochorismate, salicylate, phenol, or catechol respectively, but also those which have the natural capacity to utilize these substrates or which can be engineered to display these activities. 
       Isochorismate Synthase (ICS), Isochorismate Pyruvate Lyase (IPL), Salicylate Decarboxylase (SDC), Phenol 2-Monooxygenase (PMO), and Catechol-1,2-Dioxygenase (CDO) Activities 
       [0041]    Genes encoding ICS activity are known in the art and several have been sequenced from both microbial and plant origin. The sequence of ICS encoding genes are available (for example, see GenBank Gene ID: 945511, 946712, 881821, and 843810). Genes encoding IPL activity are known in the art and several have been sequenced from microbial origin. The sequence of IPL encoding genes are available (for example, see GenBank Gene ID: 881846). Genes encoding SDC activity are known in the art and to date only one has been sequenced from microbial origin. The sequence of SDC encoding genes are available (for example, see DDBJ ID: DM040453). Genes encoding PMO activity are known in the art and have been sequenced. The sequence of PMO encoding genes are available (for example, see GenBank Accession: L04488.1 and M60276.1). Genes encoding CDO activity are known in the art and have been sequenced. The sequence of CDO encoding genes are available (for example, see GenBank Gene ID: 3609645, 3614680, 879147, 5191661, and 5191980). 
         [0042]    It will be appreciated that the present embodiments are not limited to the genes encoding polypeptides having the specific activities mentioned above, but will encompass any suitable homologs of such genes that may be obtained by standard methods. Methods of obtaining homologs to these genes using sequence-dependent protocols are well known in the art. Examples of sequence-dependent protocols include, but are not limited to, methods of nucleic acid hybridization, and methods of DNA and RNA amplification as exemplified by various uses of nucleic acid amplification technologies (e.g., polymerase chain reaction (PCR)). 
         [0043]    For example, genes encoding homologs of the polypeptides that alone or in combination have the above mentioned activities could be isolated directly by using all or a portion of the known sequences as DNA hybridization probes to screen libraries from any desired plant, fungi, yeast, or bacteria using methodology well known to those skilled in the art. Specific oligonucleotide probes based upon the literature nucleic acid sequences can be designed and synthesized by methods known in the art. Moreover, the entire sequences can be used directly to synthesize DNA probes by methods known to those skilled in the art, such as random primers DNA labeling, nick translation, or end-labeling techniques or RNA probes using available in vitro transcription systems. In addition, specific primers can be designed and used to amplify a part of or full length of the instant sequences. The resulting amplification products can be labeled directly during amplification reactions or labeled after amplification reactions, and used as probes to isolate full-length cDNA or genomic fragments under conditions of appropriate stringency. 
       Microbial Production Hosts 
       [0044]    The production organisms of the present invention will include any organism capable of expressing the genes required for phenol production. Typically, the production organism will be restricted to microorganisms or plants. Microorganisms useful in the present invention include, but are not limited to enteric bacteria ( Escherichia  and  Salmonella , for example) as well as  Bacillus, Acinetobacter, Actinomycetes  such as  Streptomyces, Corynebacterium, Methanotrophs  such as  Methylosinus, Methylomonas, Rhodococcus  and  Pseudomonas; Cyanobacteria , such as  Rhodobacter  and  Synechocystis ; yeasts, such as  Saccharomyces, Zygosaccharomyces, Kluyveromyces, Candida, Hansenula, Debaryomyces, Mucor, Pichia , and  Torulopsis ; and filamentous fungi such as  Aspergillus  and  Arthrobotrys , and algae, for example. Co-expressing at least one gene encoding a polypeptide having ICS activity, at least one gene encoding a polypeptide having IPL activity, and at least one gene encoding a polypeptide having SDC activity can result in the production of large quantities of phenol. 
         [0045]    Although any of the above mentioned microorganisms would be useful for the production of phenol, preferred strains would be those that either natively or have been engineered to over-produce chorismate. Chorismate over-producing strains are known and include, but are not limited to,  Escherichia  sp.,  Corynebacterium  sp.,  Microbacterium  sp.,  Arthrobacter  sp.,  Pseudomonas  sp., and  Brevibacteria  sp. Particularly useful chorismate over-producing strains include, but are not limited to,  Microbacterium ammoniaphilum  ATCC 10155,  Corynebacterium lillium  NRRL-B-2243,  Corynebacterium glutamicum  ATCC 21674,  E. coli  NST74,  E. coli  NST37, and  Arthrobacter citreus  ATCC 11624. 
         [0046]    A recombinant host for phenol production may be constructed from a suitable chorismate over-producing strain by co-expressing at least one gene encoding a polypeptide having ICS activity, at least one gene encoding a polypeptide having IPL activity, and at least one gene encoding a polypeptide having SDC activity. 
         [0047]    Microbial expression systems and expression vectors containing regulatory sequences that direct high level expression of foreign proteins and over-expression of native proteins are well known to those skilled in the art. Any of these could be used to construct chimeric genes for the production of phenol, as well as its derivatives catechol and cis,cis-muconic acid. These chimeric genes could then be introduced into appropriate microorganisms via transformation to allow for expression of high levels of the enzymes. 
         [0048]    The method of production associated with embodiments of the invention involves the incorporation of genes encoding polypeptides displaying ICS, IPL, SDC, PMO, and CDO activities into a single host organism and the use of those organisms to convert renewable resources such as glucose, for example, to phenol and its derivatives, catechol and cis-cis-muconate. Thus, embodiments of the invention rely upon the identification of genes encoding ICS, IPL, SDC, PMO, and CDO activities and, preferably, those genes which when expressed in a recombinant host organism can display such activities. Candidate genes encoding ICS homologs were selected and included ICS1 from  Arabidopsis thaliana , pchA from  Pseudomonas aeruginosa , entC from  E. coli , and menF from  E. coli . Each gene was amplified from genomic DNA samples via PCR, cloned into an appropriate expression vector, and transformed into  E. coli . Candidate genes encoding IPL were selected from the open literature and included pchB from  Pseudomonas aeruginosa . Each gene was amplified from genomic DNA samples via PCR, cloned into an appropriate expression vector, and transformed into  E. coli . Candidate genes encoding SDC were selected from the open literature and included sdc from  Trichosporon moniliiforme . The gene was synthesized to include codon optimization for  E. coli , then subsequently amplified via PCR, cloned into an appropriate expression vector, and transformed into  E. coli . Candidate genes encoding PMO were selected and included the operon dmpLMNOP from  Pseudomonas  sp. CF600 and loci GI:170525 from  Trichosporon cutaneum . Candidate genes encoding CDO were selected and included catA from  Pseudomonas reinekei , salD from  Pseudomonas reinekei , and catA from  Pseudomonas putida.    
         [0049]    Where possible, screening assays were then performed on both whole cells and cell extracts. SDC activity was investigated via the conversion of exogenous salicylate to phenol, whereas PMO activity was investigated via the conversion of exogenous phenol to catechol, and CDO activity was investigated via the conversion of exogenous catechol to cis,cis-muconic acid. SDC activity was positively confirmed in recombinant  E. coli  according to both whole cell and cell extract assays in strains expressing codon optimized sdc synthesized based on the wild-type sequence of  Trichosporon moniliiforme.    
       EXAMPLES 
       [0050]    It should be understood that these Examples, while indicating preferred embodiments of the invention, are given by way of illustration only. From the above discussion and these following Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various uses and conditions. 
         [0051]    Procedures required for PCR amplification, DNA modifications by endo- and exonucleases for generating desired ends for cloning of DNA, ligation, and bacterial transformation are well known in the art. The standard molecular biology techniques used herein are well-known in the art and described by Sambook, J., Fritsch, E. F., and Maniatis, T.,  Molecular Cloning: A Laboratory Manual,  2 nd  ed.; Cold Spring Harbor Laboratory: Cold Spring Harbor, N.Y., 1989. 
         [0052]    Materials and methods suitable for the maintenance and growth of microbial cultures are well known in the art. Method and techniques suitable for use in the following set of Examples may be found for example, as described in Manual of Methods for General Bacteriology; Gerhardt, P., Murray, R. G. F., Costilow, R. N., Nester, E. W., Wood, W. A., Krieg, N. R., and Phillips, G. B., Eds., American Society for 
         [0053]    Microbiology: Washington, D.C., 1994. All reagents used in the Examples were purchased from Sigma Aldrich (St. Louis, Mo.). Restriction enzymes, polymerases, and ligase were purchased from New England Biolabs (Ipswich, Mass.). Nutrients and chemicals used for the growth and maintenance of cells were purchased from DIFCO Laboratories (Detroit, Mich.). 
       General Methods 
       [0054]    PCR reactions were performed using a BioRad iCycler system with Phusion DNA Polymerase (Finnzymes, Espoo, Finland). Custom DNA oligonucleotide primers were synthesized by and purchased from Integrated DNA Technologies (Coralville, Iowa). PCR cycling and reaction conditions were standardized according to manufacturer instructions. 
         [0055]    An HPLC assay was developed to simultaneously separate and measure aqueous metabolite concentrations in microbial cultures. For a typical assay, 1 mL culture was removed from shake flask culture and centrifuged to pellet cells. 0.75 mL of supernatant was then transferred to a sealed HPLC vial. A Hewlett Packard 1100 series HPLC system with an auto sampler and a diode array UV/Vis detector with a reverse-phase Hypersil Gold SBC18 column (4.6 mm×150 mm; Thermo Fisher, USA) was used to achieve separation and detection of the species. 5 was used to achieve separation and detection of the species. nd a diode arrayA total flow rate of 1.0 ml/min and column temperature of 45° C. were held constant throughout. The column was eluted with solvent A containing 5 mM sulfuric acid and solvent B containing acetonitrile. The eluent consists of 85% solvent A and 15% solvent B. The UV detector was used to monitor the eluent at 215 nm for phenol and salicylate. Under these conditions phenol and salicylate were eluted at 6.8 min and 12.6 min, respectively. 
         [0056]    For all culture experiments, seeds cultures were first grown in Luria Broth (LB) media overnight. Minimal media 1 (herein referred to as “MM1”) was used for fermentations which contained glucose (nominally 15 g/L), MgSO 4 .7H 2 O (0.5 g/L), NH 4 SO 4  (4.0 g/L), MOPS (24.7 g/L), KH 2 PO 4  (0.3 g/L), K 2 HPO 4  (0.7 g/L), and 5 mL/L ATCC Trace Mineral Supplement (EDTA(0.5 g/L), MgSO 4 .7H2O (3 g/L), MnSO 4 .7H 2 O (0.5 g/L), NaCl (1 g/L), FeSO 4 .7H 2 O (0.1 g/L), Co(NO 3 ) 2 .6H 2 O (0.1 g/L), CaCl 2  (0.1 g/L), ZnSO4.7H 2 O (0.1 g/L), CuSO 4 .5H 2 O (0.01 g/L), AlK(SO 4 ) 2  (0.01 g/L), H 3 BO 3  (0.01 g/L), Na 2 MoO 4 .2H 2 O (0.01 g/L), Na 2 SeO 3  (0.001 g/L), Na 2 WO 4 .2H 2 O (0.10 g/L), and NiCl 2 .6H 2 O (0.02 g/L)). 
         [0000]    Cloning of Candidate Genes Encoding ICS Activity from  E. Coli, A. Thaliana , and  P. Aeruginosa.    
         [0057]    Candidate ICS encoding genes, namely SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3, and SEQ ID NO:4 were amplified via PCR using clonal and genomic DNA templates derived from  A. thaliana  (SEQ ID NO:1),  P. aeruginosa  (SEQ ID NO:2), and  E. coli  (SEQ ID NO:3 and SEQ ID NO:4). The oligonucleotide primers used to amplify IcsI from  A. thaliana  (SEQ ID NO:1) are given as SEQ ID NO:8 and SEQ ID NO:9. The oligonucleotide primers used to amplify pchA from  P. aeruginosa  (SEQ ID NO:2) are given as SEQ ID NO:10 and SEQ ID NO:11. The oligonucleotide primers used to amplify menF from  E. coli  (SEQ ID NO:3) are given as SEQ ID NO:12 and SEQ ID NO:13. The oligonucleotide primers used to amplify entC from  E. coli  (SEQ ID NO:4) are given as SEQ ID NO:14 and SEQ ID NO:15. In all cases, amplified linear DNA fragments were subsequently cleaned using Zyppy Clean and Concentrator kit (Zymo Research, Orange, Calif.). Amplified fragments from  A. thaliana, P. aeruginosa  and  E. coli  were then treated by restriction endonuclease digestion with the enzymes BamHI and XbaI with appropriate digestion buffer for 3 h at 37° C. Samples of the expression vector pTrc99A were similarly digested with BamHI and XbaI. All digested fragments were subsequently purified using the Zyppy Gel DNA recovery kit (Zymo Research, Orange, Calif.) per manufacturer&#39;s instruction. Gene inserts and linearized plasmid DNA were then appropriately ligated together by treatment with T4 DNA ligase (New England Biolabs, Ipswich, Mass.) at 4° C. overnight. Ligase reaction mixtures were then transformed into chemically competent  E. coli  NEB10-Beta. Selection of transformants was achieved by plating transformed cells on LB solid agar media containing 100 mg/L ampicillin and culturing overnight at 37° C. Vectors with correct gene insert for all ICS encoding genes were confirmed by restriction digest analysis and colony PCR with 1 μL culture broth and appropriate primers, namely SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:14, and SEQ ID NO:15. Under these conditions, vectors containing the correct gene insert were identified as those which displayed fragments of 1.7 kb (IcsI), 1.4 kb (pchA), 1.3 kb (menF), and 1.2 kb (entC) when separated on a 0.7% w./v. agarose gel at 90V for 60 min. These cloning works resulted in the successful generation of the plasmids pTrc99A-IcsI, pTrc99A-pchA, pTrc99A-menF, and pTrc99A-entC. 
         [0000]    Cloning of Candidate Genes Encoding IPL Activity from  P. aeruginosa.    
         [0058]    Candidate IPL encoding genes, namely SEQ ID NO:5, was amplified via PCR using genomic DNA templates derived from  P. aeruginosa . The oligonucleotide primers used to amplify pchB from  P. aeruginosa  (SEQ ID NO:5) are given as SEQ ID NO:16 and SEQ ID NO:17. Amplified DNA fragments were subsequently cleaned using Zyppy Clean and Concentrator kit (Zymo Research, Orange, Calif.). Fragments were then treated by restriction enzyme digestion with appropriate enzymes and buffer for 3 h at 37° C. Amplified fragments of pchB were digested with NcoI and EcoRI for which the previously engineered vectors pTrc99A-IcsI, pTrc99A-pchA, pTrc99A-menF, and pTrc99A-entC were also digested with NcoI and EcoRI. All digested fragments were subsequently purified using the Zyppy Gel DNA recovery kit (Zymo Research, Orange, Calif.) per manufacturers instruction. Gene inserts and linearized plasmid DNA were then appropriately ligated together by treatment with T4 DNA ligase (New England Biolabs, Ipswich, Mass.) at 4° C. overnight. 
         [0059]    Ligase reaction mixtures were then transformed into chemically competent  E. coli  NEB10-Beta. Selection of transformants was achieved by plating transformed cells on LB solid agar media containing 100 mg/L ampicillin and culturing overnight at 37° C. Among the resultant transformants, the vectors with the correct insertion of the genes IcsI/pchB, pchA/pchB, menF/pchB, and entC/pchB were confirmed among clones by restriction digest analysis and colony PCR with 1 μL culture broth and appropriate primers, namely SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:14, SEQ ID NO:16, and SEQ ID NO:17. Under these conditions, vectors containing the correct gene inserts were identified as those which displayed fragments of 1.7 kb (IcsI), 1.4 kb (pchA), 1.3 kb (menF), 1.2 kb (entC), and 0.3 kb (pchB) when separated on a 0.7% w./v. agarose gel at 90V for 60 min. These cloning works resulted in the successful generation of the plasmids pTrc99A-IcsI-pchB, pTrc99A-pchA-pchB, pTrc99A-menF-pchB, and pTrc99A-entC-pchB. 
       Cloning of Candidate Genes Encoding SDC Activity. 
       [0060]    The candidate salicylate decarboxylase encoding gene, sdc_syn (SEQ ID NO:7), was amplified via PCR using a template plasmid containing a synthetic gene sequence custom synthesized for codon optimization in  E. coli  and based on the wild-type sequence of sdc from  T. moniliiforme  (SEQ ID NO:6). The oligonucleotides primers used to amplify sdc_syn (SEQ ID NO:7) are given as SEQ ID NO:18 and SEQ ID NO:19. Amplified DNA fragments were subsequently cleaned using Zyppy Clean and Concentrator kit (Zymo Research, Orange, Calif.). Amplified fragments were then treated by restriction endonuclease digestion with the enzymes NcoI and EcoRI with appropriate digestion buffer for 3 h at 37° C. A sample of the expression vector pTrcCOLAK was similarly digested with NcoI and EcoRI. Digested fragments were subsequently cleaned using Zyppy Gel DNA recovery kit (Zymo Research, Orange, Calif.). Gene inserts and linearized plasmid DNA were ligated together by treatment with T4 DNA ligase (New England Biolabs, Ipswich, Mass.) at 4° C. overnight. Ligation mixtures were subsequently transformed into chemically competent  E. coli  NEB10-beta (New England Biolabs, Ipswich, Mass.). Selection of transformants was achieved by plating transformed cells on LB solid agar media containing 35 mg/L kanamycin and culturing overnight at 37° C. Vectors with correct gene insert for all SDC encoding genes were confirmed by restriction digest analysis and colony PCR with 1 μL culture broth and appropriate primers, namely SEQ ID NO:18 and SEQ ID NO:19. Under these conditions, vectors containing the correct gene insert were identified as those which displayed a fragment of 1.0 kb (sdc) when separated on a 0.7% w./v. agarose gel at 90V for 60 min. This cloning effort resulted in the successful generation of the plasmid pTrcCOLAK-sdc_syn. 
       Example 1 
     Assaying SDC Activity in Recombinant  E. Coli.    
       [0061]    SDC activity was investigated using a whole cell assay.  E. coli  BW25113(DE3) was first transformed with pTrcCOLAK-sdc_syn. Selection was performed on LB agar supplemented with 35 mg/L kanamycin and screened for said resistance. This resulted in the construction of the strain  E. coli  BW25113(DE3) pTrcCOLAK-sdc_syn. Two seed cultures of  E. coli  BW25113(DE3) pTrcCOLAK-sdc_syn consisting of 5 ml of LB broth containing 100 mg/L ampicillin and 35 mg/L kanamycin were prepared and grown overnight at 37° C. while shaking at 200 rpm. 1 mL of each culture was used to inoculate 3×250 mL shake flasks containing 50 mL of LB supplemented with 100 mg/L ampicillin and 35 mg/L kanamycin. Cultures were grown at 30° C. while shaking at 200 rpm for 6 h at 30° C. before being induced with IPTG to a final concentration of 0.2 mM. Induced cultures were then allowed to grow overnight at 30° C. while shaking at 200 rpm. Cells were then collected by centrifugation in 50 ml Falcon tubes for 5 min at 1400×g and washed once with PBS (phosphate buffered saline, pH 7) buffer. The entire cell pellet was then resuspended in 30 ml PBS supplemented with 400 mg/L salicylate. The results for this assay are shown in  FIG. 2 , which show that expression of pTrcCOLAK-sdc_syn in  E. coli  BW25113(DE3) results in the conversion of salicylate to phenol at a final titer greater than 100 mg/L phenol. 
         [0062]    These results demonstrate how SDC activity can be attained in recombinant  E. coli  by the expression of a gene whose sequence is given by SEQ ID NO:7. These results further establish the generation of recombinant  E. coli  strains that are specifically capable of converting salicylate to phenol. 
       Example 2 
     Co-Expression of ICS, IPL, and SDC Encoding Enzymes in  E. Coli  NST 74 to Convert Glucose to Phenol in Flask Cultures. 
       [0063]    The previously-engineered phenylalanine over-producing strain  E. coli  NST74 was co-transformed with plasmids pTrc99A-menF-pchB and pTrcCOLAK-sdc_syn, and pTrc99A-entC-pchB and pTrcCOLAK-sdc_syn. The previously-engineered phenylalanine over-producing strain  E. coli  NST74 ΔpheAΔAtyrA was co-transformed with plasmids pTrc99A-IcsI-pchB and pTrcCOLAK-sdc_syn. Selection was performed on LB agar supplemented with 100 mg/L ampicillin and 35 mg/L kanamycin and screened for said resistances. This resulted in the construction of the strains (1)  E. coli  NST74 pTrc99A-menF-pchB pTrcCOLAK-sdc_syn, (2)  E. coli  NST74 pTrc99A-entC-pchB pTrcCOLAK-sdc_syn, and (3)  E. coli  NST74 ΔpheAΔtyrA pTrc99A-IcsI-pchB pTrcCOLAK-sdc_syn. Single colonies were then selected from the resultant transformants and those strains were grown in 5 mL LB broth supplemented with both 100 mg/L ampicillin and 35 mg/L kanamycin. These seed cultures were grown for 12 hours at 32° C. with shaking at 250 rpm. 1 ml of each seed culture was then used to inoculate 50 mL MM1 supplemented with 100 mg/L ampicillin and 35 mg/L kanamycin. These cultures were performed in 250 mL shake flasks. The cells were then grown at 30° C. with shaking at 250 rpm to an OD 600  ˜0.6 prior to being induced by the addition of IPTG to a final concentration of 0.4 mM. 1 ml samples were taken from each culture at intervals of 0, 24, 48, and 72 hours post induction and analyzed for metabolite content via HPLC-DAD using methods described herein. The obtained results are shown in  FIG. 3 . As can be seen, all three strains are capable of producing phenol from glucose, with  E. coli  NST74 pTrc99A-entC-pchB pTrcCOLAK-sdc_syn in particular producing phenol to a final titer of greater than 440 mg/L after 72 h. 
         [0064]    These results illustrate how a strain of  E. coli  can be constructed to synthesize phenol as a dominant product when supplied with glucose as a sole carbon and energy source. The invention describes a process in which recombinant  E. coli  has been engineered to co-express enzymes that display both ICS, IPL and SDC activities. In the preferred embodiments, the  E. coli  host strain will be a chorismate over-producing strain, ICS activity will be encoded by menF or entC from  E. coli , IPL activity will be encoded by pchB from  P. aeruginosa , and SDC activity will be encoded by a gene whose sequence is given by (SEQ ID NO:7). 
         [0065]    Accordingly, the embodiments described and illustrated above provide a method for the production of phenol comprising:
       i) contacting a recombinant host cell with a fermentable carbon source, said recombinant host comprising:
           a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity   
           ii) growing said recombinant cell for a time sufficient to produce phenol       
 
         [0071]    Additionally, the embodiments described and illustrated above provide a method for the production of catechol comprising:
       i) contacting a recombinant host cell with a fermentable carbon source, said recombinant host comprising:
           a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity; and   d) at least one gene encoding a polypeptide having phenol 2-monooxygenase activity   
           ii) growing said recombinant cell for a time sufficient to produce catechol       
 
         [0078]    Additionally, the embodiments described and illustrated above provide a method for the production of cis,cis-muconate comprising:
       i) contacting a recombinant host cell with a fermentable carbon source, said recombinant host comprising:
           a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity; and   d) at least one gene encoding a polypeptide having phenol 2-monooxygenase activity; and   e) at least one gene encoding a polypeptide having catechol-1,2-dioxygenase activity   
           ii) growing said recombinant cell for a time sufficient to produce cis,cis-muconate       
 
         [0086]    Additionally, the embodiments described and illustrated above provide a recombinant host cell comprising:
       a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity       
 
         [0090]    Additionally, the embodiments described and illustrated above provide a recombinant host cell comprising:
       a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity; and   d) at least one gene encoding a polypeptide having phenol 2-monooxygenase activity       
 
         [0095]    Additionally, the embodiments described and illustrated above provide a recombinant host cell comprising:
       a) at least one gene encoding a polypeptide having isochorismate synthase activity; and   b) at least one gene encoding a polypeptide having isochorismate pyruvate lyase activity; and   c) at least one gene encoding a polypeptide having salicylate decarboxylase activity; and   d) at least one gene encoding a polypeptide having phenol 2-monooxygenase activity; and   e) at least one gene encoding a polypeptide having catechol 1,2-dioxygenase activity       
 
         [0101]    The materials and methods described above are not intended to be limited to the embodiments and examples described herein.