Patent Publication Number: US-11384369-B2

Title: Microorganisms and methods for the production of glycolic acid and glycine via reverse glyoxylate shunt

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/806,195 filed Feb. 15, 2019, entitled “MICROORGANISMS AND METHODS FOR THE PRODUCTION OF GLYCOLIC ACID AND GLYCINE VIA REVERSE GLYOXYLATE SHUNT”, the disclosure of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This application relates to recombinant microorganisms for the biosynthesis and yield improvement of glycolic acid and/or glycine from glyoxylate using a reverse glyoxylate shunt and methods of producing the recombinant microorganisms. The application further relates to methods of producing glycolic acid and/or glycine from a carbon source such as a hexose or a pentose feedstock via a reverse glyoxylate shunt using the recombinant microorganisms. The application further relates to compositions comprising one or more of these compounds and/or the recombinant microorganisms. 
     STATEMENT REGARDING SEQUENCE LISTING 
     The Sequence Listing associated with this application is provided in text format in lieu of a paper copy, and is hereby incorporated by reference into the specification. The name of the text file containing the Sequence Listing is BRSK-010_02US_ST25.txt. The text file is about 45.5 KB, was created on Feb. 14, 2020, and is being submitted electronically via EFS-Web. 
     BACKGROUND 
     Glycolic acid and glycine are valuable raw materials in the production of a number of compounds. For example, glycolic acid is an important raw material in the production of products like polyglycolic acid and other biocompatible copolymers. Similarly, glycine has a number of uses in the pharmaceutical and cosmetic industry, pesticide production (pyrethroid insecticides), and as food and feed additive. 
     To develop environmentally friendly processes for the production of glycolic acid (GA) and glycine, researchers have engineered microorganisms with biosynthetic pathways to produce GA and/or glycine. For example, U.S. Pat. Nos. 9,034,615 and 8,945,888 disclose production of glycolic acid via a glyoxylate shunt (GS) pathway. U.S. Pre-grant Publication No. 2014/0295510 discloses a GS pathway in eukaryotes for production of glycolic acid while patent documents such as WO 2017/059236, WO 2016/079440, US 2016/0076061 and US 2015/0147794 disclose production of glycolic acid using pentose-based sugars. Although the biochemical pathways described in these and other patent documents are developed with an aim to provide high GA and glycine yields, the yields of GA and glycine provided by these routes are still not optimal because these pathways generate excess NADH and excess CO 2 , which result in loss of product yield. 
     The present invention provides biosynthetic pathways to produce glycolic acid and glycine at higher theoretical yield potential compared to existing metabolic pathways, solving or, in part, reducing the problem of lost product yield potential. The present invention provides biosynthetic pathways, wherein carbon fixation enzymes and reverse glyoxylate shunt enzymes are coupled to produce and increase yield of glycolic acid and glycine. The present invention also provides further improvements to prevent carbon loss from previously described pathways, and to favor carbon fixation coupling to the reverse glyoxylate shunt. 
     The present invention also aims to further increase theoretical yield of glycolic acid and glycine of previously described pathways, in part by utilizing CO 2  and/or NAD(P)H released by these pathways or by capturing carbon sources (CO 2 , HCO 3− , or other carbonates) exogenously provided. The present invention additionally provides biosynthetic pathways to produce and improve GA and glycine yield potential of previously described pathways, rerouting carbon flow via carbon fixation in the pyruvate and/or phosphoenolpyruvate node towards oxaloacetate, in part diminishing or even abolishing carbon loss in metabolic and enzymatic reactions native to the microorganism. 
     Thus, the present invention allows higher production of GA and glycine using the same amount of starting carbon source (e.g. sugars) and provides ways to increase the economic success of current methods. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides recombinant microorganisms and uses thereof. Also provided are methods of making the recombinant microorganism. In various embodiments, the recombinant microorganism of the present disclosure produce glycolic acid (GA) and/or glycine via glyoxylate as the intermediate. 
     In some embodiments, provided herein is a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, wherein the microorganism comprises: (a) a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA. 
     In some embodiments, provided herein is a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. 
     In some embodiments, provided herein is a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate; (c) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (d) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. In some of these embodiments, the recombinant microorganism may comprise a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate. 
     In some embodiments, provided herein is a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the recombinant microorganism does not catalyze the conversion of oxaloacetate to malate. 
     In some embodiments, provided herein is a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. In these embodiments, this recombinant microorganism has a reduced phosphoglucose isomerase activity or, more preferably, does not catalyze the conversion of glucose-6-phosphate to fructose-6-phosphate by the enzyme phosphoglucose isomerase. Additionally, this recombinant microorganism may or may not comprise endogenous or exogenous enzymes citrate synthase, isocitrate lyase and/or glyoxylate reductase overexpressed. By reducing the activity of the phosphoglucose isomerase, or more preferably by deleting the gene which encodes the phosphoglucose isomerase (gene pgi in  E. coli , for example) that catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate, the carbon source can be at least partially diverted towards the pentose-phosphate pathway (PPP) in order to provide additional NADPH potentially required for optimal conversion of glyoxylate into glycolate. In some embodiments, the CO 2  generated through the PPP route can potentially be re-incorporated by the use of the carboxylase and carboxykinase enzymes herein proposed. 
     The recombinant microorganisms of any one of the embodiments described herein may not produce isopropyl alcohol, ethanol, acetone, citric acid, itaconic acid, acetic acid, butyric acid, (poly-)3-hydroxybutyric acid, 3-hydroxyisobutyric acid, 3-aminoisobutyric acid, 2-hydroxyisobutyric acid, methacrylic acid, (poly)glutamic acid, glutamic acid, arginine, ornithine, citrulline, leucine, isoleucine, or proline via the acetyl-CoA produced by the malyl coenzyme A lyase. 
     In the recombinant microorganisms of the present disclosure, the acetyl-CoA produced by the malyl coenzyme A lyase is expected to combine with the OAA to increase the biosynthesis of GA and/or glycine. 
     In some embodiments, any one of the recombinant microorganisms described herein may comprise a deletion or loss of function mutation in the gene encoding malate dehydrogenase, wherein the mutation results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate, malate to pyruvate and/or malate to oxaloacetate. 
     In the embodiments, where the recombinant microorganisms produce glycolic acid, the recombinant microorganism comprises a gene encoding NADH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate and/or a gene encoding NADPH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate. 
     In the embodiments, where the recombinant microorganisms produce glycine, the recombinant microorganism comprises a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase to catalyze the conversion of glyoxylate to glycine. 
     In some embodiments, the recombinant microorganisms of the present disclosure may produce both glycolic acid and glycine and would comprise one or more of the genes described above that convert glyoxylate to GA and/or glycine. 
     In some embodiments, the gene encoding glyoxylate reductase activity is selected from the group consisting of: ycdW and/or yiaE from  E. coli , GOR1 from  S. cerevisiae , gyaR from  Thermococcus litoralis , and/or GLYR1 from  A. thaliana . The present disclosure also contemplates the use of homologs of these genes to catalyze the conversion of glyoxylate to glycolate. 
     In some embodiments, the malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate in the recombinant microorganisms of the present disclosure is from the Enzyme Classification (E.C.) 1.1.1.38, E.C. 1.1.1.39, or E.C. 1.1.1.40. 
     In some embodiments, the malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate in the recombinant microorganisms of the present disclosure is from the Enzyme Classification (E.C.) 1.1.1.37. 
     In some embodiments, the gene encoding the malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate in the recombinant microorganisms of the present disclosure is selected from the group consisting of: maeA, maeB, dme, mez, mae1, nad-me1, nad-me2, and homologs thereof. In these embodiments, the gene maeA can be from  E. coli, Pseudomonas , or  Bacillus ; the gene maeB can be from  E. coli  or  Salmonella ; the gene dme can be from  Rhizobium ; the gene mez can be from  Mycobacterium ; the gene mae1 can be from  S. cerevisiae ; and the gene nad-me1 or nad-me2 can be from  Arabidopsis thaliana . For example, the gene maeA can be from  B. subtilis ; the gene dme can be from  R. melilote ; or the gene mez can be from  Mycobacterium tuberculosis . The present disclosure also contemplates the use of homologs of these genes to catalyze the carboxylation of pyruvate to malate. 
     In some embodiments, the gene encoding the malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate in the recombinant microorganisms of the present disclosure is selected from the group consisting of: gene mdh from  E. coli, Corynebacterium, Streptomyces, Saccharomyces  and  Arabidopsis . For example, the gene mdh can be from  S. coelicolor  or gene mdh1/2/3 from  S. cerevisiae . The present disclosure also contemplates the use of homologs of these genes to catalyze the conversion of oxaloacetate to malate. 
     In some embodiments, the malate thiokinase that converts malate to malyl coenzyme A can be from the Enzyme Classification System No. E.C. 6.2.1.4, E.C. 6.2.1.5, E.C. 6.2.1.9, or E.C. 6.2.1.-. 
     In some embodiments, the gene encoding malate thiokinase in the recombinant microorganisms of the present disclosure can be sucCD and/or SucCD-2 and/or mtkAB from  Methylobacterium  sp.,  Methylobacterium extorquens, Escherichia coli, Thermus thermophiles, Hyphomicrobium  sp.,  Methanocaldococcus jannaschii, Methanothermobacter thermautotrophicus, Rhizobium, Methylococcus capsulatus  or  Pseudomonas ; or homologs thereof. 
     In some embodiments, the malyl coenzyme A lyase that converts malyl coenzyme A to glyoxylate and acetyl-CoA is from the E.C. 4.3.1.24 or E.C. 4.3.1.25. 
     In some embodiments, the gene encoding malyl coenzyme A lyase in the recombinant microorganisms of the present disclosure can be mcl and/or Mcl1 and/or mclA from  Methylobacterium extorquens, Rhodobacter sphaeroides, Streptomyces, Chloroflexus aurantiacus, Nitrosomonas europaea, Methylococcus capsulans, Nereida ignava, Hyphomicrobium methylovorum, Thalassobius activus, Roseobacter litoralis, Hyphomicrobium denitrficans, R sphaeroides, Mycobacterium smegmatis  or  Rhodococcus fascians ; or homologs thereof. 
     In some embodiments, the pyruvate carboxylase that converts pyruvate to OAA can be from the Enzyme Classification System No. E.C. 6.4.1.1; the phosphoenolpyruvate carboxylase that converts phosphoenolpyruvate to OAA can be from the E.C. 4.1.1.31; the phosphoenolpyruvate carboxykinase that converts phosphoenolpyruvate to OAA can be from the E.C. 4.1.1.32 and E.C. 4.1.1.49. 
     In some embodiments, the gene encoding pyruvate carboxylase in the recombinant microorganisms of the present disclosure can be pyc from  Rhizobium etli , PYC1 or PYC2 from yeast or pyc from  B. subtilis ; or homologs thereof. 
     In some embodiments, the gene encoding phosphoenolpyruvate carboxylase in the recombinant microorganisms of the present disclosure can be ppc from  E. coli , ppc or pepC from  R. marinus , ppcA from  M. thermautotrophicus , pep1 from  Z. mays , ppc1/2/3 from  A. thaliana , ppc from  G. max  or is from  Rhodothermus, Corynebacterium, Salmonella, Hyphomicrobium, Streptococcus, Streptomyces, Pantoea, Bacillus, Clostridium, Pseudomonas, Rhodopseudomonas, Nicotiana tabacum, Amaranthus hypochondriacus, Triticum aestivum  or  Medicago sativa ; or homologs thereof. 
     In some embodiments, the gene encoding phosphoenolpyruvate carboxykinase in the recombinant microorganisms of the present disclosure can be pck or pckA from  Escherichia coli , pckA from  Selenomonas ruminantium , pckA from  Salmonella typhimurium , pckA from  Klebsiella  sp., pckA from  Thermus  sp, pck or pckA from  Ruminococcus albus  or  Ruminococcus flavefaciens , pckA from  Actinobacillus succinogenes , pck or pckA from  Streptococcus bovis , or from  Bacillus, Ruminiclostridium thermocellum, Klebsiella, Mycobacterium ; or homologs thereof. 
     In some embodiments, the recombinant microorganisms of the present disclosure comprise: (a) a gene encoding citrate synthase to convert OAA and acetyl-coA produced by the malyl-coA lyase to citrate; (b) a gene encoding citrate hydro-lyase to convert citrate to cis-aconitate; (c) a gene encoding D-threo-isocitrate hydro-lyase or aconitase to convert cis-aconitate to isocitrate; (d) a gene encoding isocitrate lyase to convert isocitrate to succinate and glyoxylate; (e) a gene encoding succinate dehydrogenase to convert succinate to fumarate; and (f) a gene encoding fumarase to convert fumarate to malate. In the same embodiment, the recombinant microorganisms may have the malate dehydrogenase that catalyzes the conversion of malate to oxaloacetate at least partially preserved. Alternatively, the malate dehydrogenase that catalyzes the conversion of malate to oxaloacetate may be down-regulated or even inactivated to favor the activity of the malate thiokinase enzyme. 
     In some embodiments, the recombinant microorganisms of the present disclosure may comprise a loss of function mutation or deletion of the gene encoding malate synthase. Exemplary genes encoding the malate synthase include aceB and/or glcB from  E. coli  or DAL7 and/or MLS1 from yeast, e.g.,  S. cerevisiae.    
     The recombinant microorganisms of any one of the embodiments disclosed herein may comprise a deletion or modification that decreases the activity of one or more endogenous genes selected from the group consisting of: (a) a gene encoding isocitrate dehydrogenase; (b) a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase; (c) a gene encoding pyruvate kinase; and (d) a gene encoding glycolate oxidase. Exemplary genes encoding isocitrate dehydrogenase include icd from  E. coli  or IDP2 and/or IDH1/2 from yeast. Exemplary genes encoding pyruvate dehydrogenase include aceE and/or aceF from  E. coli . Exemplary genes encoding pyruvate kinase include pykA and/or pykF from  E. coli . Exemplary genes encoding glycolate oxidase include glcD, glcE, glcF, and/or glcG from  E. coli . Exemplary genes. 
     The recombinant microorganism of any one of the embodiments disclosed herein may comprise a deletion or modification that decreases the activity of the pyruvate dehydrogenase, preventing or at least diminishing a major carbon loss from pyruvate conversion to acetyl-CoA, and favoring the carbon rerouting from pyruvate or phosphoenolpyruvate into oxaloacetate via carboxylation activity of enzyme candidates proposed herein. 
     The recombinant microorganism of any one of the embodiments disclosed herein may comprise a deletion or modification that decreases the activity of the pyruvate kinase, favoring the carbon fixation of phosphoenolpyruvate into oxaloacetate via carboxylation activity of enzyme candidates proposed herein. 
     The recombinant microorganisms of any one of the embodiments disclosed herein may comprise a deletion or modification that decreases the activity of one or more endogenous genes selected from the group consisting of: (a) a gene encoding glyoxylate carboligase; (b) a gene encoding 2-oxo-4-hydroxyglutarate aldolase; (c) a gene encoding glycoaldehyde reductase; and (d) a gene encoding a repressor of isocitrate lyase. An exemplary gene encoding glyoxylate carboligase is gcl. An exemplary gene encoding 2-oxo-4-hydroxyglutarate aldolase is edA. Exemplary genes encoding glycoaldehyde reductase include fucO and gldA. An exemplary gene encoding the repressor of isocitrate lyase is iclR. 
     In some embodiments, in the recombinant microorganisms of the present disclosure, the level of expression of a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase is increased. 
     In some embodiments, in the recombinant microorganisms of the present disclosure, the level of expression of a gene encoding alanine transaminase and/or a gene encoding NADPH-dependent glutamate synthase is increased. 
     In some embodiments, in the recombinant microorganisms of the present disclosure, the synthesis of glycolic acid and/or glycine is increased by increasing the level of expression or the activity or the specificity of at least one enzyme selected from the group consisting of: pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate thiokinase, malyl coenzyme A lyase, alanine-glyoxylate aminotransferase, glycine dehydrogenase, glycine transaminase, serine-glyoxylate transaminase, glycine oxidase, NADH-dependent glyoxylate reductase, and NADPH-dependent glyoxylate reductase. 
     In some embodiments, in the recombinant microorganisms of the present disclosure, the synthesis of glycolic acid and/or glycine is increased by decreasing the level of expression or the activity or the specificity of at least one enzyme selected from the group consisting of: malate synthase, isocitrate dehydrogenase, pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase, pyruvate kinase, glyoxylate carboligase, 2-oxo-4-hydroxyglutarate aldolase, glucose-6-phosphate isomerase, glycoaldehyde reductase, and glycolate oxidase. 
     In some embodiments, in the recombinant microorganisms of the present disclosure, the synthesis of glycolic acid and/or glycine is increased by decreasing the level of expression of a gene encoding a repressor of isocitrate lyase. 
     In some embodiments, the recombinant microorganisms of the present disclosure may utilize NADH and CO 2  generated by other glycolic acid and/or glycine producing pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. For example, in some embodiments, the recombinant microorganisms of the present disclosure may utilize NADH and/or CO 2  generated by a serine/hydroxypyruvate-based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. In some embodiments, the recombinant microorganisms of the present disclosure may utilize NADH and/or CO 2  generated by a glyoxylate shunt pathway in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. In some embodiments, the recombinant microorganisms of the present disclosure may utilize NADH and/or CO 2  generated by a D-erythrose to glycoaldehyde based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. In some embodiments, the recombinant microorganisms of the present disclosure may utilize NADH and/or CO 2  generated by a pentose derivative to glycoaldehyde based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. 
     In some embodiments, the recombinant microorganisms of the present disclosure may utilize exogenously added CO 2 , a carbonate, and/or a reducing agent in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase. The reducing agent can be hydrogen, electrons, and/or NAD(P)H. 
     The recombinant microorganisms provided by the present disclosure include bacterium, yeast, and fungus. In some embodiments, the recombinant microorganism of the present disclosure can be a bacterium selected from the group consisting of Enterobacteriaceae, Clostridiaceae, Bacillaceae, Streptomycetaceae, and Corynebacteriaceae. In an exemplary embodiment, the recombinant microorganism of the present disclosure can be a species of  Escherichia, Clostridium, Bacillus, Klebsiella, Pantoea, Salmonella, Lactobacillus , or  Corynebacterium . For example, the recombinant microorganism of the present disclosure can be  Escherichia coli, Corynebacterium glutamicum, Clostridium acetobutylicum , or  Bacillus subtilis.    
     In some embodiments, the recombinant microorganism of the present disclosure can be a yeast selected from the family Saccharomycetaceae. In an exemplary embodiment, the recombinant microorganism of the present disclosure can be a species of  Saccharomyces . For example, the recombinant microorganism of the present disclosure can be  Saccharomyces cerevisiae.    
     In the recombinant microorganisms of the present disclosure, any one of the genes described herein are expressed heterologously. 
     The present disclosure also provides methods of producing GA and/or glycine using the recombinant microorganisms described herein. In some embodiments, methods for producing glycolic acid and/or glycine using the recombinant microorganisms described herein comprise cultivating the recombinant microorganism in a culture medium containing a feedstock providing a carbon source until the glycolic acid and/or glycine are produced. 
     In some embodiments, the carbon source used in the methods of producing GA and/or glycine can be selected from the group consisting of: sugars, glycerol, alcohols, organic acids, alkanes, fatty acids, hemicellulose, lignocellulose, proteins, carbon dioxide, and carbon monoxide. In exemplary embodiments, the carbon source is a hexose and/or pentose sugar. In an exemplary embodiment, the carbon source is glucose. In another exemplary embodiment, the carbon source is sucrose. In another exemplary embodiment, the carbon source comprises a biomass hydrolysate comprising hemicellulose. In another exemplary embodiment, the carbon source is CO 2  or carbonate such as HCO 3   − . 
     Also provided herein are methods of producing recombinant microorganisms that produce glycolic acid and/or glycine from glyoxylate. 
     In some embodiments, a method of producing a recombinant microorganism that produces glycolic acid and/or glycine comprises introducing into the microorganism: (a) a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA. 
     In some embodiments, a method of producing a recombinant microorganism that produces glycolic acid and/or glycine comprises introducing into the microorganism: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate; (c) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (d) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. In some of these embodiments, the method may comprise introducing into the microorganism a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate. 
     In some embodiments, a method of producing a recombinant microorganism that produces glycolic acid and/or glycine comprises introducing into the microorganism: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the recombinant microorganism does not catalyze the conversion of oxaloacetate to malate. 
     In an exemplary embodiment, the gene encoding malate dehydrogenase introduced into the microorganism heterogeneously comprises a mutation that results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate, malate to pyruvate or malate to oxaloacetate. In another exemplary embodiment, if the gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate and/or oxaloacetate to malate is present endogenously in the recombinant microorganism, then the method for producing the recombinant microorganism that produces glycolic acid and/or glycine comprises introducing a mutation into the endogenous gene encoding malate dehydrogenase, wherein the mutation results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate, malate to pyruvate or malate to oxaloacetate. 
     In some embodiments, the methods for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing into the microorganism; (a) a gene encoding NADH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate; (b) a gene encoding NADPH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate; and/or c) a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase that catalyzes the conversion of glyoxylate to glycine. 
     In some embodiments, the methods for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing into the microorganism a loss of function mutation or deletion of the gene encoding malate synthase. 
     In some embodiments, the method for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing into the microorganism a deletion or modification that reduces the activity of one or more enzymes encoded by the genes selected from the group consisting of: (a) a gene encoding isocitrate dehydrogenase; (b) a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase; (c) a gene encoding pyruvate kinase; and (d) a gene encoding glycolate oxidase. 
     In some embodiments, the method for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing into the microorganism a deletion or modification that reduces the activity of one or more enzymes encoded by the genes selected from the group consisting of: (a) a gene encoding glyoxylate carboligase; (b) a gene encoding 2-oxo-4-hydroxyglutarate aldolase; (c) a gene encoding glycoaldehyde reductase; and (d) a gene encoding a repressor of isocitrate lyase. 
     In some embodiments, the method for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing a gain of function mutation into the gene encoding alanine-glyoxylate aminotransferase, the gene encoding alanine-glyoxylate aminotransferase glyoxylate to glycine, the gene encoding glycine dehydrogenase, the gene encoding glycine transaminase, the gene encoding serine-glyoxylate transaminase, and/or the gene encoding glycine oxidase that catalyze the conversion of glyoxylate to glycine. 
     In some embodiments, the method for producing a recombinant microorganism that produces glycolic acid and/or glycine may further comprise introducing a gain of function mutation into a gene encoding alanine transaminase and/or a gene encoding NADPH-dependent glutamate synthase. 
     In the embodiments where a gain of function mutation is introduced into a gene, the gain of function mutation may be introduced into the gene that is endogenous to the microorganism or a gain of function mutation may be introduced into a heterogeneous gene and introducing the heterogeneous gene comprising the gain of function mutation into the microorganism. 
     The microorganisms that may be used to produce the recombinant microorganisms of the present disclosure include bacterium, yeast, and fungus. Exemplary bacteria that may be used in the present disclosure include bacteria selected from the group consisting of Enterobacteriaceae, Clostridiaceae, Bacillaceae, Streptomycetaceae, and Corynebacteriaceae. For example, the recombinant microorganism can be a species of  Escherichia , e.g.  Escherichia coli, Clostridium , e.g.,  Clostridium acetobutylicum, Bacillus , e.g.  Bacillus subtilis, Klebsiella, Pantoea, Salmonella, Lactobacillus , or  Corynebacterium , e.g.  Corynebacterium glutamicum.    
     Exemplary yeast that may be used to produce the recombinant microorganisms of the present disclosure can be from the family Saccharomycetaceae. For example, the recombinant microorganism can be a species of  Saccharomyces , e.g.  Saccharomyces cerevisiae.    
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a schematic of glycolic acid (GA) and glycine (Gly) production via the reverse glyoxylate shunt. The symbol   means enzymes to be potentially down regulated or inactivated/abolished, ie. respective gene potentially attenuated or deleted. 
         FIG. 2  illustrates a schematic of co-utilization of known glycolic acid (GA) and glycine (Gly) production pathways with the reverse glyoxylate shunt pathway of the present disclosure. Dashed lines show reaction summaries. The symbol   means enzymes to be potentially down regulated or inactivated/abolished, ie. respective gene potentially attenuated or deleted. 
         FIG. 3  is a schematic depicting a flux map towards maximal theoretical production yield of GA from glucose, using a hexokinase transport system, carboxylation via phosphoenolpyruvate carboxykinase (PEPCK), phosphoenolpyruvate carboxylase (PPC) or pyruvate carboxylase (PYC), and the combination of the glyoxylate shunt (GS) and reverse gyloxylate shunt (rGS). Flux analysis was based on the use of a NADPH-dependent glyoxylate reductase enzyme candidate. Flux values are normalized against the glucose input. 
         FIG. 4  is a schematic depicting a flux map towards maximal theoretical production yield of GA from glucose, using a phosphotransferase system (PTS) transport system, carboxylation via PEPCK, PPC or PYC, and the combination of the GS and rGS. Flux analysis was based on the use of a NADPH-dependent glyoxylate reductase enzyme candidate. Flux values are normalized against the glucose input. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     The following definitions and abbreviations are to be used for the interpretation of the disclosure. 
     As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an enzyme” includes a plurality of such enzymes and reference to “the microorganism” includes reference to one or more microorganisms, and so forth. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having, “contains,” “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. A composition, mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive “or” and not to an exclusive “or.” 
     The terms “about” and “around,” as used herein to modify a numerical value, indicate a close range surrounding that explicit value. If “X” were the value, “about X” or “around X” would indicate a value from 0.9X to 1.1X, or, in some embodiments, a value from 0.95X to 1.05X. Any reference to “about X” or “around X” specifically indicates at least the values X, 0.95X, 0.96X, 0.97X, 0.98X, 0.99X, 1.01X, 1.02X, 1.03X, 1.04X, and 1.05X. Thus, “about X” and “around X” are intended to teach and provide written description support for a claim limitation of, e.g., “0.98X.” 
     As used herein, the terms “microbial,” “microbial organism,” and “microorganism” include any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya, the latter including yeast and filamentous fungi, protozoa, algae, or higher Protista. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea, and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. Also included are cell cultures of any species that can be cultured for the production of a chemical. 
     As described herein, in some embodiments, the recombinant microorganisms are prokaryotic microorganism. In some embodiments, the prokaryotic microorganisms are bacteria. “Bacteria”, or “eubacteria”, refers to a domain of prokaryotic organisms. Bacteria include at least eleven distinct groups as follows: (1) Gram-positive (gram+) bacteria, of which there are two major subdivisions: (1) high G+C group ( Actinomycetes, Mycobacteria, Micrococcus , others) (2) low G+C group ( Bacillus, Clostridia, Lactobacillus, Staphylococci, Streptococci, Mycoplasmas ); (2) Proteobacteria, e.g., Purple photosynthetic+non-photosynthetic Gram-negative bacteria (includes most “common” Gram-negative bacteria); (3) Cyanobacteria, e.g., oxygenic phototrophs; (4) Spirochetes and related species; (5)  Planctomyces ; (6)  Bacteroides, Flavobacteria ; (7)  Chlamydia ; (8) Green sulfur bacteria; (9) Green non-sulfur bacteria (also anaerobic phototrophs); (10) Radioresistant micrococci and relatives; (11)  Thermotoga  and  Thermosipho thermophiles.    
     “Gram-negative bacteria” include cocci, nonenteric rods, and enteric rods. The genera of Gram-negative bacteria include, for example,  Neisseria, Spirillum, Pasteurella, Brucella, Yersinia, Francisella, Haemophilus, Bordetella, Escherichia, Salmonella, Shigella, Klebsiella, Proteus, Vibrio, Pseudomonas, Bacteroides, Acetobacter, Aerobacter, Agrobacterium, Azotobacter, Spirilla, Serratia, Vibrio, Rhizobium, Chlamydia, Rickettsia, Treponema , and  Fusobacterium.    
     “Gram positive bacteria” include cocci, nonsporulating rods, and sporulating rods. The genera of gram positive bacteria include, for example,  Actinomyces, Bacillus, Clostridium, Corynebacterium, Erysipelothrix, Lactobacillus, Listeria, Mycobacterium, Myxococcus, Nocardia, Staphylococcus, Streptococcus , and  Streptomyces.    
     The term “recombinant microorganism” and “recombinant host cell” are used interchangeably herein and refer to microorganisms that have been genetically modified to express or to overexpress endogenous enzymes, to express heterologous enzymes, such as those included in a vector, in an integration construct, or which have an alteration in expression of an endogenous gene. By “alteration” it is meant that the expression of the gene, or level of a RNA molecule or equivalent RNA molecules encoding one or more polypeptides or polypeptide subunits, or activity of one or more polypeptides or polypeptide subunits is up regulated or down regulated, such that expression, level, or activity is greater than or less than that observed in the absence of the alteration. It is understood that the terms “recombinant microorganism” and “recombinant host cell” refer not only to the particular recombinant microorganism but to the progeny or potential progeny of such a microorganism. 
     The term “expression” with respect to a gene sequence refers to transcription of the gene and, as appropriate, translation of the resulting mRNA transcript to a protein. Thus, as will be clear from the context, expression of a protein results from transcription and translation of the open reading frame sequence. The level of expression of a desired product in a host cell may be determined on the basis of either the amount of corresponding mRNA that is present in the cell, or the amount of the desired product encoded by the selected sequence. For example, mRNA transcribed from a selected sequence can be quantitated by qRT-PCR or by Northern hybridization (see Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press (1989)). Protein encoded by a selected sequence can be quantitated by various methods, e.g., by ELISA, by assaying for the biological activity of the protein, or by employing assays that are independent of such activity, such as western blotting or radioimmunoassay, using antibodies that recognize and bind the protein. See Sambrook et al., 1989, supra. 
     The term “decreasing” or “reducing” the level of expression of a gene or an enzyme activity refers to the partial or complete suppression of the expression of a gene or enzyme activity. This suppression of expression or activity can be either an inhibition of the expression of the gene, a deletion of all or part of the promoter region necessary for the gene expression, a deletion in the coding region of the gene, or the replacement of the wild-type promoter by a weaker natural or synthetic promoter. For example, a gene may be completely deleted and may be replaced by a selection marker gene that facilitates the identification, isolation and purification of the strains according to the invention. Alternatively, endogenous genes may be knocked out or deleted to favor the new metabolic pathway. In yet another embodiment, the expression of the gene may be decreased or reduced by using a weak promoter or by introducing certain mutations. 
     As used herein, the term “non-naturally occurring,” when used in reference to a microorganism organism or enzyme activity of the disclosure, is intended to mean that the microorganism organism or enzyme has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microorganism&#39;s genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous, or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary non-naturally occurring microorganism or enzyme activity includes the hydroxylation activity described above. 
     The term “exogenous” as used herein with reference to various molecules, e.g., polynucleotides, polypeptides, enzymes, etc., refers to molecules that are not normally or naturally found in and/or produced by a given yeast, bacterium, organism, microorganism, or cell in nature. 
     On the other hand, the term “endogenous” or “native” as used herein with reference to various molecules, e.g., polynucleotides, polypeptides, enzymes, etc., refers to molecules that are normally or naturally found in and/or produced by a given yeast, bacterium, organism, microorganism, or cell in nature. 
     The term “heterologous” as used herein in the context of a modified host cell refers to various molecules, e.g., polynucleotides, polypeptides, enzymes, etc., wherein at least one of the following is true: (a) the molecule(s) is/are foreign (“exogenous”) to (i.e., not naturally found in) the host cell; (b) the molecule(s) is/are naturally found in (e.g., is “endogenous to”) a given host microorganism or host cell but is either produced in an unnatural location or in an unnatural amount in the cell; and/or (c) the molecule(s) differ(s) in nucleotide or amino acid sequence from the endogenous nucleotide or amino acid sequence(s) such that the molecule differing in nucleotide or amino acid sequence from the endogenous nucleotide or amino acid is produced in an unnatural (e.g., greater than naturally found) amount in the cell. The heterologous expression of polynucleotides can be via the introduction of one or more vectors (e.g., plasmids, cosmids, viral vectors, etc.) comprising the gene of interest into the host microorganism or via the integration of a construct comprising the gene of interest into the genome of the host microorganism. 
     The term “homolog,” as used herein with respect to an original enzyme or gene of a first family or species, refers to distinct enzymes or genes of a second family or species which are determined by functional, structural, or genomic analyses to be an enzyme or gene of the second family or species which corresponds to the original enzyme or gene of the first family or species. Homologs most often have functional, structural, or genomic similarities. Techniques are known by which homologs of an enzyme or gene can readily be cloned using genetic probes and PCR. Identity of cloned sequences as homologs can be confirmed using functional assays and/or by genomic mapping of the genes. 
     A protein has “homology” or is “homologous” to a second protein if the amino acid sequence encoded by a gene has a similar amino acid sequence to that of the second gene. Alternatively, a protein has homology to a second protein if the two proteins have “similar” amino acid sequences. Thus, the term “homologous proteins” is intended to mean that the two proteins have similar amino acid sequences. In certain instances, the homology between two proteins is indicative of its shared ancestry, related by evolution. The terms “homologous sequences” or “homologs” are thought, believed, or known to be functionally related. A functional relationship may be indicated in any one of a number of ways, including, but not limited to: (a) degree of sequence identity and/or (b) the same or similar biological function. Preferably, both (a) and (b) are indicated. The degree of sequence identity may vary, but in one embodiment, is at least 50% (when using standard sequence alignment programs known in the art), at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least 98.5%, or at least about 99%, or at least 99.5%, or at least 99.8%, or at least 99.9%. Homology can be determined using software programs readily available in the art, such as those discussed in Current Protocols in Molecular Biology (F. M. Ausubel et al., eds., 1987) Supplement 30, section 7.718, Table 7.71. Some alignment programs are MacVector (Oxford Molecular Ltd, Oxford, U.K.) and ALIGN Plus (Scientific and Educational Software, Pennsylvania). Other non-limiting alignment programs include Sequencher (Gene Codes, Ann Arbor, Mich.), AlignX, and Vector NTI (Invitrogen, Carlsbad, Calif.). A similar biological function may include, but is not limited to: catalyzing the same or similar enzymatic reaction; having the same or similar selectivity for a substrate or co-factor; having the same or similar stability; having the same or similar tolerance to various fermentation conditions (temperature, pH, etc.); and/or having the same or similar tolerance to various metabolic substrates, products, by-products, intermediates, etc. The degree of similarity in biological function may vary, but in one embodiment, is at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, or at least 98.5%, or at least about 99%, or at least 99.5%, or at least 99.8%, or at least 99.9%, according to one or more assays known to one skilled in the art to determine a given biological function. 
     The term “variant” refers to any polypeptide or enzyme described herein. A variant also encompasses one or more components of a multimer, multimers comprising an individual component, multimers comprising multiples of an individual component (e.g., multimers of a reference molecule), a chemical breakdown product, and a biological breakdown product. In particular, non-limiting embodiments, an enzyme may be a “variant” relative to a reference enzyme by virtue of alteration(s) in any part of the polypeptide sequence encoding the reference enzyme. A variant of a reference enzyme can have enzyme activity of at least 10%, at least 30%, at least 50%, at least 80%, at least 90%, at least 100%, at least 105%, at least 110%, at least 120%, at least 130% or more in a standard assay used to measure enzyme activity of a preparation of the reference enzyme. In some embodiments, a variant may also refer to polypeptides having at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the full-length, or unprocessed enzymes of the present disclosure. In some embodiments, a variant may also refer to polypeptides having at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the mature, or processed enzymes of the present disclosure. 
     The term “yield potential” as used herein refers to a yield of a product from a biosynthetic pathway. In one embodiment, the yield potential may be expressed as a percent by weight of end product per weight of starting compound. 
     The term “thermodynamic maximum yield” as used herein refers to the maximum yield of a product obtained from fermentation of a given feedstock, such as glucose, based on the energetic value of the product compared to the feedstock. In a normal fermentation, without use of additional energy sources such as light, hydrogen gas or methane or electricity, for instance, the product cannot contain more energy than the feedstock. The thermodynamic maximum yield signifies a product yield at which all energy and mass from the feedstock is converted to the product. This yield can be calculated and is independent of a specific pathway. If a specific pathway towards a product has a lower yield than the thermodynamic maximum yield, then it loses mass and can most likely be improved upon or substituted with a more efficient pathway towards the product. 
     The term “redox balance” refers to the overall amount of redox cofactors in a given set of reactions. When there is a shortage of redox cofactors, the redox balance is negative and the yield of such pathway would not be realistic since there is a need to burn feedstock to fulfill the cofactor demand. When there is a surplus of redox cofactors, the redox balance is said to be positive and the yield of such pathway is lower than the maximum yield (Dugar et al. “Relative potential of biosynthetic pathways for biofuels and bio-based products” Nature biotechnology 29.12 (2011): 1074). In addition, when the pathway produces the same amount of redox cofactors as it consumes, the redox balance is zero and one can refer to this pathway as “redox balanced”. Designing metabolic pathways and engineering an organism such that the redox cofactors are balanced or close to being balanced usually results in a more efficient, higher yield production of the desired compounds when compared to an unbalanced pathway. Redox reactions always occur together as two half-reactions happening simultaneously, one being an oxidation reaction and the other a reduction reaction. In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing agent gains electrons and is reduced. In one embodiment, the redox reactions take place in a biological system. The term redox state is often used to describe the balance of NAD+/NADH and NADP+/NADPH of natural or non-natural metabolic pathways in a biological system such as a microbial cell. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate, and acetoacetate), whose interconversion is dependent on these ratios. In one embodiment, an external source of hydrogen or electrons, combined or not with the use of hydrogenase enzymes able to convert hydrogen to NAD(P)H, may be beneficial to increase product yield in metabolic pathways with negative redox balance, i.e., when there is a shortage in redox cofactors, such as NAD(P)H. 
     Introduction 
     The glyoxylate shunt (GS) (also called glyoxylate cycle) is a variation of the tricarboxylic acid cycle (TCA cycle) and is an anabolic pathway occurring in plants, bacteria, protists, and fungi. The TCA cycle and the glyoxylate shunt differ in that in the glyoxylate shunt, isocitrate is cleaved into glyoxylate and succinate by isocitrate lyase instead of being decarboxylated and dehydrogenated to α-ketoglutarate. This bypasses the two decarboxylation steps that take place in the TCA cycle allowing acetyl-CoA to be converted to TCA cycle intermediates without carbon loss. Glyoxylate is converted into malate by incorporating a molecule of acetyl-CoA. 
     Production of glycolic acid using a glyoxylate shunt (GS) pathway is described in U.S. Pat. No. 9,034,615, which is incorporated by reference herein in its entirety. This patent discloses GA production by attenuating the glyoxylate consuming pathways and by increasing the activity of NAD(P)H-dependent glyoxylate reductase. Use of the glyoxylate shunt pathway for production of glycolic acid is also disclosed in U.S. Pat. No. 8,945,888; U.S. Pre-Grant Publication No. 2014/0295510; and PCT Publication No. WO 2016/193540, which are incorporated by reference herein in their entireties. However, the glyoxylate shunt pathway has a reduced total yield potential of 0.84 g_GA/g_glucose, while the thermodynamic maximum yield for a glucose→GA conversion is 1.70 g/g. This pathway is also not redox balanced and has a high excess of 4 mol NADH and 2 mol quinol per mol of consumed glucose, all of which needs to be re-oxidized for the cell to be viable. The overall stoichiometry of this pathway and the yield potential can be summarized as follows: Glucose→2 GA+2 CO 2 +4 NADH+2 quinol+2 ATP; y=0.84 g/g, 49% of Y(max)=1.70 g/g. 
     GA production via a pentose derivative to glycolaldehyde-based pathways are described in PCT Publication Nos. WO 2017/059236 and WO 2016/79440 and U.S. Pre-grant Publication Nos. US 2016/0076061 and US 2015/0147794, all of which are incorporated by reference herein in their entirety. However, these pathways also have a reduced total yield potential. For example, GA production using xylose as a source has a reduced yield potential of 1.01 g_GA/g_xylose, while the thermodynamic maximum yield for a xylose→GA conversion is 1.71 g/g. The overall stoichiometry of the xylose-based pathway and the yield potential can be summarized as follows: Xylose→2 GA+1 CO 2 +3 NADH+1 quinol+0 ATP; y=1.01 g/g, 59% of Y(max)=1.71 g/g. As can be seen from the equation, the xylose-based pathway also produces excess of NADH and CO 2 . 
     PCT Publication No. WO 2015/181074, incorporated by reference herein in its entirety, discloses a method for the production of D-erythrose and subsequent conversion of D-erythrose into glycoaldehyde. Glycoaldehyde can be further converted into glycolic acid and/or glycine. This pathway has a reduced yield potential of 1.27 g_GA/g_glucose, while the thermodynamic maximum yield is 1.70 g/g. The overall stoichiometry of the erythrose-based pathway and the yield potential can be summarized as follows: Glucose→3 GA+2 NADH+1 quinol−1 ATP, y=1.27 g/g, 75% of Y(max)=1.70 g/g. This pathway is not redox balanced and has a high excess of 2 mol NADH and 1 mol quinol per mol of consumed glucose, all of which needs to be re-oxidized for the cell to be viable. 
     A serine/hydroxypyruvate pathway for the GA production is described in U.S. Pat. No. 8,911,978, which is incorporated by reference herein in its entirety. 
     All of these pathways generate excess NADH and release excess CO 2 , i.e., these pathways do not reach the thermodynamic possible maximum yield. They typically oxidize more sugar carbon than necessary to CO 2 , thereby loosing product yield. 
     The present application relates to glyoxylate producing recombinant microorganisms having one or more biosynthetic pathways for the production of glycolic acid (GA) and/or glycine. In one embodiment, the glyoxylate producing recombinant microorganisms of the present invention comprise a reverse glyoxylate shunt based route that increases the yield of GA and glycine. In another embodiment, the glyoxylate producing recombinant microorganisms of the present invention comprise previously described metabolic pathways and modifications for the production of GA and/or glycine and a reverse glyoxylate shunt based route that further increases the yield of GA and glycine. The terms “glycolic acid” and “glycolate” are used interchangeably throughout this disclosure. 
     Certain patent documents disclose reverse glyoxylate shunt pathways. For example, U.S. Pat. No. 9,410,131 discloses a reverse glyoxylate shunt pathway to produce oxaloacetate and malonyl-CoA. U.S. Pre-grant Publication No. 2016/369292 discloses the use of reverse glyoxylate shunt to produce isocitrate and acetyl-CoA. EP Patent No. 2738247B1 discloses the use of reverse glyoxylate shunt for the acetyl-CoA production. However, none of these patent documents disclose a reverse glyoxylate shunt to increase the production of glyoxylate and subsequently the production of glycolic acid and/or glycine. Moreover, none of these patent documents disclose a reverse glyoxylate shunt wherein the acetyl-CoA generated from the activity of malyl-CoA lyase is reincorporated into the metabolic pathway, e.g. by combining with oxaloacetate to produce citrate in the glyoxylate shunt, for the increased production of glycolic acid and/or glycine. 
     The present disclosure provides, for the first time, a carbon-fixing route for GA or glycine production, making it a suitable co-pathway for most of the current GA and glycine pathways with CO 2  and NADH excess. By providing a suitable co-pathway, the present disclosure solves the problem of NADH excess of all glycolic acid (GA) and glycine pathways described so far and enables higher GA and glycine yield than previously described pathways alone, including recently published high yield pathways using xylose. 
     The present disclosure provides, for the first time, a reverse glyoxylate shunt pathway that utilizes a carboxylation reaction for the production of GA and glycine. None of the GA or glycine producing pathways described so far utilizes a carboxylation reaction for the synthesis of GA or glycine. 
     In certain embodiments, the carboxylation-based reverse glyoxylate shunt pathway of the present disclosure can be utilized synergistically with known GA or glycine producing pathways. 
     The present disclosure encompasses the use of homologs as well as natural or engineered variants of the genes and/or the enzymes encoded by these genes described herein. 
     Microorganisms, Pathways, and Methods of the Invention 
     In one embodiment, the present disclosure provides a glyoxylate producing recombinant microorganism that produces glycolic acid and/or glycine from glyoxylate using a reverse glyoxylate shunt pathway. The expression of the reverse glyoxylate shunt pathway increases the production of glyoxylate as an intermediate and increases the production of final products, glycolic acid and glycine. In some embodiments, the glyoxylate producing recombinant microorganisms of the present invention co-produce glycolic acid and glycine. In another embodiment, the glyoxylate producing recombinant microorganism of the present invention co-produce glycolic acid and another co-product such as, but not limited to, succinate or lactate. In a further embodiment, the glyoxylate producing recombinant microorganism of the present invention co-produce glycine and another co-product such as, but not limited to, succinate or lactate. 
     In some embodiments, the present disclosure provides a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. 
     In some embodiments, the present disclosure provides a glyoxylate producing recombinant microorganism for the synthesis of glycolic acid and/or glycine, wherein the microorganism comprises: (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. In these embodiments, this recombinant microorganism has a reduced phosphoglucose isomerase activity or, more preferably, does not catalyze the conversion of glucose-6-phosphate to fructose-6-phosphate by the enzyme phosphoglucose isomerase. Additionally, this recombinant microorganism may or may not comprise endogenous or exogenous enzymes citrate synthase, isocitrate lyase and/or glyoxylate reductase overexpressed. By reducing the activity of the phosphoglucose isomerase, or more preferably by deleting the gene which encodes the phosphoglucose isomerase (gene pgi in  E. coli , for example) that catalyzes the conversion of glucose-6-phosphate into fructose-6-phosphate, the carbon source can be at least partially diverted towards the pentose-phosphate pathway (PPP) in order to provide additional NADPH potentially required for optimal conversion of glyoxylate into glycolate. In some embodiments, the CO 2  generated through the PPP route can potentially be re-incorporated by the use of the carboxylase and carboxykinase enzymes herein proposed. 
     In one embodiment, the reverse glyoxylate shunt based pathway of the present disclosure comprises carboxylating pyruvate to malate; converting malate to malyl-Coenzyme A (CoA) and converting malyl-CoA to glyoxylate and acetyl-CoA. Accordingly, in one embodiment, provided herein is a recombinant microorganism that comprises a gene encoding malate dehydrogenase to convert pyruvate to malate, a gene encoding malate thiokinase to convert malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl coenzyme A. In one embodiment, the gene encoding malate dehydrogenase encodes for a modified malate dehydrogenase that catalyzes the conversion of pyruvate to malate but does not catalyze the reverse reaction of malate to pyruvate or shows reduced conversion of malate to pyruvate. In some embodiments, the gene encoding the malate dehydrogenase may comprise a deletion or loss of function mutation. The modified malate dehydrogenase can be a naturally occurring variant or an engineered variant. 
     In another embodiment, the reverse glyoxylate shunt based pathway of the present disclosure comprises carboxylating phosphoenol pyruvate (PEP) and/or pyruvate to oxaloacetate (OAA); converting OAA to malate; converting malate to malyl-Coenzyme A (CoA) and converting malyl-CoA to glyoxylate and acetyl-CoA. Accordingly, in one embodiment, provided herein is a recombinant microorganism that comprises a gene encoding pyruvate carboxylase to convert pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase to convert phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase to convert phosphoenolpyruvate to OAA in combination with a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate, a gene encoding malate thiokinase to convert malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl coenzyme A. 
     In another embodiment, the reverse glyoxylate shunt based pathway of the present disclosure comprises carboxylating phosphoenol pyruvate (PEP) or pyruvate to oxaloacetate (OAA) and/or carboxylating pyruvate to malate; converting OAA to malate; converting malate to malyl-Coenzyme A (CoA) and converting malyl-CoA to glyoxylate and acetyl-CoA. Accordingly, in one embodiment, provided herein is a recombinant microorganism that comprises a gene encoding pyruvate carboxylase to convert pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase to convert phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase to convert phosphoenolpyruvate to OAA; and/or a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate; a gene encoding malate thiokinase to convert malate to malyl coenzyme A; and a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl coenzyme A. In one embodiment, the gene encoding malate dehydrogenase encodes for a modified malate dehydrogenase that catalyzes the conversion of pyruvate to malate or OAA to malate but does not catalyze the reverse reaction of malate to pyruvate or malate to OAA or shows reduced conversion of malate to pyruvate or malate to OAA. The modified malate dehydrogenase can be a naturally occurring variant or an engineered variant. 
     In another embodiment, the reverse glyoxylate shunt based pathway of the present disclosure comprises carboxylating phosphoenol pyruvate (PEP) and/or pyruvate to oxaloacetate (OAA); converting malate to malyl-Coenzyme A (CoA) and converting malyl-CoA to glyoxylate and acetyl-CoA; wherein the reverse glyoxylate shunt pathway does not comprise converting OAA to malate. Accordingly, in one embodiment, provided herein is a recombinant microorganism that comprises a gene encoding pyruvate carboxylase to convert pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase to convert phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase to convert phosphoenolpyruvate to OAA; a gene encoding malate thiokinase to convert malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl coenzyme A, wherein the microorganism does not comprise a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate or comprises a loss-of-function mutation in the gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate. 
     In another embodiment, the reverse glyoxylate shunt based pathway of the present disclosure comprises carboxylating phosphoenol pyruvate (PEP) and/or pyruvate to oxaloacetate (OAA); carboxylating pyruvate to malate; converting malate to malyl-Coenzyme A (CoA) and converting malyl-CoA to glyoxylate and acetyl-CoA; wherein the reverse glyoxylate shunt pathway does not comprise converting OAA to malate. Accordingly, in one embodiment, provided herein is a recombinant microorganism that comprises a gene encoding pyruvate carboxylase to convert pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase to convert phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase to convert phosphoenolpyruvate to OAA; a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; a gene encoding malate thiokinase to convert malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl coenzyme A, wherein the microorganism does not comprise a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate or comprises a deletion or loss-of-function mutation in the gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate. 
     Glyoxylate produced by the reverse glyoxylate shunt and other pathways can be converted to glycolic acid and/or glycine. To increase the production of GA, the recombinant microorganism of any one of the embodiments disclosed herein may comprise a gene encoding NAD(P)H-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate. In one embodiment, the recombinant microorganism may over-express NAD(P)H-dependent glyoxylate reductase to increase the yield of GA. In another embodiment, the recombinant microorganism of any one of the embodiments disclosed herein may comprise a gain of function mutation in the gene encoding NAD(P)H-dependent glyoxylate reductase so that the activity of NAD(P)H-dependent glyoxylate reductase is increased compared to a microorganism lacking such mutation. 
     The term “NAD(P)H dependent” as used herein encompasses both NADH-dependent as well as NADPH-dependent enzymatic activity. 
     To increase the production of glycine, the recombinant microorganism of any one of the embodiments disclosed herein may comprise one or more genes encoding enzymes that catalyze the glyoxylate to glycine conversion. For example, the recombinant microorganism of any one of the embodiments disclosed herein may comprise a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase. In one embodiment, the recombinant microorganism of any one of the embodiments disclosed herein may over-express one or more of these genes to increase the yield of glycine. In another embodiment, the recombinant microorganism of any one of the embodiments disclosed herein may comprise a gain of function mutation in one or more of the above-described genes encoding glycine-producing enzymes so that the activity of these genes is increased compared to a microorganism lacking such mutation. 
     In one embodiment, the recombinant microorganisms of the present disclosure does not produce malonyl-CoA via the rGS pathway. 
     The recombinant microorganisms of the present invention comprise a gene encoding malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate and/or the reduction of OAA to malate. In one embodiment, the malate dehydrogenase that catalyzes the conversion of OAA to malate is from, but not limited to, the Enzyme Class (E.C.) 1.1.1.37. In another embodiment, the malate dehydrogenase that catalyzes the conversion of malate to OAA is from the EC 1.1.5.4. The malate dehydrogenase that catalyzes the conversion of malate to OAA is also known as malate:quinone oxidoreductase. In certain embodiments, the malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate is from, but not limited to, the Enzyme Class (E.C.) 1.1.1.38, E.C. 1.1.1.39, or E.C. 1.1.1.40. 
     In one embodiment, the recombinant microorganisms of the present disclosure comprise a gene encoding malate dehydrogenase, wherein the malate dehydrogenase can catalyze the conversion of pyruvate to malate and/or OAA to malate but does not catalyze or catalyzes with reduced efficiency the reverse reaction from malate to pyruvate or malate to OAA. In one embodiment, the recombinant microorganisms of the present disclosure comprise a gene encoding malate dehydrogenase, wherein the malate dehydrogenase can catalyze the conversion of oxaloacetate to malate but not the conversion of pyruvate to malate or malate to pyruvate. In one embodiment, the gene encoding malate dehydrogenase may comprise a mutation that results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate or malate to oxaloacetate or pyruvate to malate or malate to pyruvate. 
     In exemplary embodiments, the gene encoding malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate is from, but not limited to, bacteria, such as  Escherichia  (e.g., gene maeA or maeB from  E. coli ),  Pseudomonas, Bacillus  (e.g., gene maeA from  Bacillus subtilis ),  Rhizobium  (e.g., gene dme from  R. melilote ),  Mycobacterium  (e.g., gene mez from  Mycobacterium tuberculosis ),  Salmonella  (e.g., gene maeB from; or from yeast such as (e.g., gene mae1 from  S. cerevisiae ); or from plant (e.g., gene nad-me1 or nad-me2 or nad-me3 or nadp-me1 or nadp-me2 from  Arabidopsis thaliana ). 
     In exemplary embodiments, the gene encoding the malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate is from, but not limited to, bacteria, such as  Escherichia  (e.g., gene mdh from  E. coli ),  Corynebacterium, Streptomyces  (e.g., gene mdh from  S. coelicolor ); or from yeast, such as  Saccharomyces  (e.g., gene mdh1/2/3 from  S. cerevisiae ); or from plant, such as  Arabidopsis . In another embodiment, the gene encoding the malate dehydrogenase that catalyzes the conversion of malate to oxaloacetate (also known as malate:quinone oxidoreductase) is from, but not limited to,  Escherichia  (e.g., gene mqo from  E. coli ),  Pseudomonas  (e.g., gene mqo from  P. putida ) or  Bacillus  sp. 
     Malate is converted to malyl CoA by malate thiokinase activity (also known as malate-CoA ligase or malyl-CoA synthetase) or by succinyl-CoA ligase activity (also known as succinyl-CoA synthetase). In one embodiment, the malate thiokinase is from, but not limited to, EC 6.2.1.4, EC 6.2.1.5, EC 6.2.1.9 or EC 6.2.1.-. In an exemplary embodiment, the gene encoding malate thiokinase or succinyl-CoA ligase is from bacteria such as  Escherichia  (e.g., gene sucCD-2 from  E. coli ),  Thermus thermophiles, Clostridium kluyveri, Bacillus subtilis, Methanocaldococcus  (e.g., gene mtkAB or sucCD from  M. jannaschii ),  Staphylococcus aureus, Methanothermobacter thermautotrophicus, Pseudomonas, Methylococcus  sp.,  Methylobacterium  (e.g., gene mtkAB or sucCD from  M. extorquens ),  Nitrosomonas europaea, Granulibacter bethesdensis, Mesorhizobium japonicum, Hyphomicrobium methylovorum, Hyphomicrobium denitrificans, Methylococcus capsulatus, Rhodobacteraceae bacterium  or  Rhizobium . In one embodiment, the malate thiokinase or the succinyl-CoA ligase has high activity and/or specificity to malate and low activity and/or specificity to other compounds, such as succinate. This can be achieved via enzyme engineering. 
     Malyl CoA is converted into glyoxylate and acetyl-CoA by malyl CoA lyase. In one embodiment, malyl coA lyase is from, but not limited to, EC 4.1.3.24 or EC 4.1.3.25. In an exemplary embodiment, the gene encoding malyl-CoA lyase is from  Methylobacterium  (e.g., gene mclA from  M. extorquens ),  Methylobacterium extorquens, Thalassobius activus, Rhodobacter  (e.g., gene mcl1 from  R. sphaeroides ),  Roseobacter litoralis, Streptomyces, Streptococcus, Mycobacterium  (e.g., gene mcl1 from  M. smegmatis ),  Hyphomicrobium methylovorum, Roseobacter  (e.g., gene mcl1  R. litoralis ),  Nitrosomonas europaea, Cupriavidus necator, Chloroflexus  (e.g., gene mcl from  C. aurantiacus ),  Nereida  (e.g., gene mcl1 from  N. ignava ),  Hyphomicrobium denitrificans, Rhodococcus fascians.    
     The carboxylation of PEP to oxaloacetate is catalyzed by phosphoenolpyruvate carboxylase or phosphoenolpyruvate carboxykinase. In one embodiment, the PEP carboxylase is from, but not limited to, EC 4.1.1.31. In an exemplary embodiment, the gene encoding PEP carboxylase is from, but not limited to, bacteria, such as  Escherichia  (e.g., gene ppc from  E. coli ),  Rhodothermus  (e.g., gene ppc or pepC from  R. marinus ),  Corynebacterium, Salmonella, Hyphomicrobium, Streptococcus, Streptomyces, Pantoea, Bacillus, Clostridium, Pseudomonas, Rhodopseudomonas, Methanothermobacter  (e.g., gene ppcA from  M. thermautotrophicus ); plant, such as  Saccharum  hybrid, Glycine (e.g., gene ppc from  G. max ),  Nicotiana tabacum, Amaranthus hypochondriacus, Triticum aestivum, Medicago sativa, Zea mays  (e.g., gene pep1) or  Arabidopsis  (e.g., genes ppc1 or ppc2 or ppc3 from  A. thaliana ); archaea or yeast. In one embodiment, phosphoenolpyruvate carboxykinase is from, but not limited to, EC 4.1.1.32 or EC 4.1.1.49. In an exemplary embodiment, the encoding PEP carboxykinase is from, but not limited to, bacteria such as  Escherichia  (e.g., gene pck or pckA from  E. coli ),  Selenomonas  (e.g., gene pckA from  S. ruminantium ),  Salmonella  (e.g., gene pckA from  S. typhimurium ),  Mycobacterium, Pseudomonas, Rhodopseudomonas, Clostridium, Thermococcus, Streptococcus  (e.g., gene pck or pckA from  S. bovis ),  Ruminococcus  (e.g., pck or pckA from  R. albus  or  R. flavefaciens )  Actinobacillus  (e.g., gene pckA from  A. succinogenes ),  Bacillus, Ruminiclostridium thermocellum, Klebsiella, Thermus ; yeast, such as  Saccharomyces  (e.g., gene pck1 or pepc or ppc1 from  S. cerevisiae ); or  Trypanosoma  (e.g., gene from  T. brucei ). 
     The carboxylation of pyruvate to oxaloacetate is catalyzed by pyruvate carboxylase. In one embodiment, pyruvate carboxylase is from, but not limited to, EC 6.4.1.1. In an exemplary embodiment, the gene encoding pyruvate carboxylase is from bacteria such as  Bacillus  (e.g., gene pyc from  B. subtilis ),  Candida  (e.g., gene pyc1 from  C. glabrata ),  Cupriavidus  (e.g., gene pyc1 from  C. necator ),  Mycobacterium  (e.g., gene pyc from  M. smegmatis ),  Corynebacterium  (e.g., gene pyc from  C. glyciniphilum ),  Nocardia  (e.g., gene pyc1 from  N. nova ); or yeast such as  Saccharomyces  (e.g., gene pyc1 and pyc2 from  S. cerevisiae ),  Pichia  (e.g., pyc from  P. pastoris ); or  Caenorhabditis  (e.g., pyc from  C. elegans ); or from  Homo sapiens.    
     Glyoxylate can be reduced by NADH-glyoxylate reductase or by NADPH-glyoxylate reductase to produce glycolate. In one embodiment, NADH-glyoxylate reductase is from EC 1.1.1.26. In one embodiment, NADPH-glyoxylate reductase is from EC 1.1.1.79. In an exemplary embodiment, the gene encoding NADH or NADPH-dependent glyoxylate reductase activity is the gene “ycdW/ghrA” and/or “yiaE” in  E. coli , gene “GLYR1” from  A. thaliana , gene “GOR1” from  S. cerevisiae , and “gyaR” from  Thermococcus litoralis . In some embodiments, the cofactor preference (NADH or NADPH) of the enzyme can be altered through enzyme engineering. In some embodiments, the enzyme NADPH-dependent glyoxylate reductase, codified by the genes “ycdW/ghrA” or “yiaE” from  E. coli  or “GLYR1” from  A. thaliana , is engineered to become a NADH-dependent glyoxylate reductase enzyme, accepting NADH as well as the naturally enzyme accepted the cofactor NADPH, and still showing the same performance for the glyoxylate to glycolate conversion (i.e., cofactor switch without compromising its kinetic parameters for the desired reaction). 
     In one embodiment, the production of glyoxylate and ultimately the production of glycolic acid and/or glycine can be increased by co-utilization of the rGS pathway with the glyoxylate shunt (GS) pathway. For example, the acetyl-CoA generated in the rGS pathway, i.e. from the activity of the malyl-CoA lyase on malyl-CoA, can be reincorporated into the metabolic pathway in order to further increase the production of glyoxylate: i.e., by entering the GS pathway by combining with OAA to produce citrate, citrate is converted to isocitrate, isocitrate is converted to succinate and glyoxylate. The succinate produced by the GS pathway can be converted to malate via fumarate and the malate produced via this route can enter the rGS pathway where it is converted to malyl coenzyme A, which is further converted to glyoxylate and acetyl coenzyme A. 
     In recombinant microorganisms of the present invention, the rGS pathway may run first followed by the GS pathway or the GS pathway may run first followed by the rGS pathway. 
     In one embodiment of the co-utilization of the rGS and GS pathways, PEP can be converted to OAA (PEP carboxylase or PEP carboxykinase) and/or pyruvate can be converted to OAA (pyruvate carboxylase) or to malate (malate dehydrogenase); OAA can be converted to malate (malate dehydrogenase); malate can be converted to malyl-CoA (malate thiokinase); malyl-CoA can be converted to glyoxylate and acetyl-CoA (malyl-CoA lyase); acetyl-CoA can combine with OAA to form citrate (citrate synthase); citrate can be converted to cis-aconitate (citrate hydro-lyase); cis-aconitate can be converted to isocitrate (D-threo-isocitrate hydro-lyase or aconitase); isocitrate can be converted to succinate and glyoxylate (isocitrate lyase); succinate can be converted to fumarate (succinate dehydrogenase); and fumarate can be converted to malate (fumarase). Malate can re-enter the rGS pathway and can be converted to malyl-CoA. 
     In another embodiment of the co-utilization of the rGS and GS pathways, PEP can be converted to OAA (PEP carboxylase or PEP carboxykinase) and/or pyruvate can be converted to OAA (pyruvate carboxylase) or to malate (malate dehydrogenase); OAA can be converted to citrate by combining with acetyl-CoA (citrate synthase); citrate can be converted to cis-aconitate (citrate hydro-lyase); cis-aconitate can be converted to isocitrate (D-threo-isocitrate hydro-lyase or aconitase); isocitrate can be converted to succinate and glyoxylate (isocitrate lyase); succinate can be converted to fumarate (succinate dehydrogenase); fumarate can be converted to malate (fumarase); and malate can be converted to malyl-CoA (malate thiokinase) and malyl-CoA can be converted to glyoxylate and acetyl-CoA. In this embodiment, OAA may be exclusively combined with acetyl-CoA to form citrate (i.e. by blocking the conversion of OAA to malate, e.g. by inactivating the enzyme malate dehydrogenase that catalyzes the conversion of OAA to malate) or part of it may be converted to malate. 
     The recombinant microorganism of any one of the embodiments disclosed herein may comprise genes encoding enzymes involved in the GS pathway. In one embodiment, the recombinant microorganism comprises (a) a gene encoding citrate synthase to convert acetyl-coA and OAA to citrate; (b) a gene encoding citrate hydro-lyase to convert citrate to cis-aconitate; (c) a gene encoding D-threo-isocitrate hydro-lyase or aconitase to convert cis-aconitate to isocitrate; (d) a gene encoding isocitrate lyase to convert isocitrate to succinate and glyoxylate; (e) a gene encoding succinate dehydrogenase to convert succinate to fumarate; and (f) a gene encoding fumarase to convert fumarate to malate. 
     The glyoxylate produced by the GS and rGS pathway could be converted to malate by malate synthase. However, this reaction would decrease the yield of glyoxylate and thereby decrease the production of GA and glycine. Accordingly, in one embodiment, the recombinant microorganisms described herein may comprise a loss-of-function mutation in the gene encoding malate synthase. The loss-of-function mutations as referred to herein may result in a complete or partial loss of function. The loss of function mutation may also include a complete deletion of the gene of interest. In an exemplary embodiment, the genes encoding malate synthase that may be inactivated according to the present disclosure include aceB and/or glcB in  E. coli  or DAL7 and MLS1 in  S. cerevisiae.    
     In one embodiment, depending on the amount of excess NADH in a given pathway, the flux ratio of co-utilized rGS and GS is adapted to obtain lowest possible net NADH production for optimal yield. 
     One or more genes disclosed herein encoding the enzymes of interest may be present endogenously, may be inserted into the genome of the microorganism and/or expressed via one or more vectors (e.g., plasmids, cosmids, viral vectors, etc.) introduced into the microorganism. A high level of enzyme activity can be obtained by using or inserting one or several copies of the genes on the genome that can be introduced by methods of recombination known to a person of ordinary skill in the field. For expression via vectors, different types of vectors such as plasmids that differ with respect to their origin of replication and thus their copy number in the cell can be used. Exemplary plasmids for expressing the genes of interests include, but are not limited to, pSK bluescript II, pSC101, RK2, pACYC, pRSF1010, etc). The genes encoding the enzymatic polypeptides may be expressed using promoters with different strength that may or may not to be induced by inducer molecules. Examples of the promoters include Ptrc, Ptac, Plac, the lambda promoter cI or other promoters known to a person of ordinary skill in the field. Expression of the genes may also be boosted by elements stabilizing the corresponding messenger RNA (Carrier and Keasling (1998) Biotechnol. Prog. 15, 58-64) or the protein (e.g. GST tags, Amersham Biosciences). 
     In one embodiment, the endogenous glyoxylate shunt (GS) pathway and/or other central metabolic pathways in the recombinant microorganism may be modified, for example, by avoiding competing routes or by-products formation and bypassing carbon loss reactions to maximize the carbon flow to the biosynthesis of glycolic acid and/or glycine through the reverse glyoxylate shunt. For example, in one embodiment, the recombinant microorganism comprising the rGS pathway may be modified to delete or attenuate the expression of at least one gene encoding an enzyme selected from the group consisting of: 
     (a) malate synthase (e.g. genes aceB and/or glcB in  E. coli  or genes DAL7 and MLS1 in  S. cerevisiae ); 
     (b) isocitrate dehydrogenase (e.g. gene icd in  E. coli  or genes IDP2 and IDH1/2 in  S. cerevisiae ); 
     (c) pyruvate dehydrogenase (e.g. genes pdhc and/or lpd in  E. coli ), pyruvate oxidase (e.g. gene poxB in  E. coli ) and/or pyruvate formate-lyase (e.g. gene pfl in  E. coli ); and 
     (d) pyruvate kinase (e.g. genes pykA and/or pykF in  E. coli ). 
     In some embodiments, endogenous glyoxylate consuming routes in the recombinant microorganism comprising the rGS pathway may be deleted or attenuated to further increase the yield of glycolic acid and/or glycine. For example, in one embodiment, the recombinant microorganism comprising the rGS pathway is modified to delete or attenuate the expression of or inhibit the activity of at least one gene selected from the group consisting of: 
     (a) a gene encoding glyoxylate carboligase (e.g. gene gcl in  E. coli ); 
     (b) a gene encoding 2-oxo-4-hydroxyglutarate aldolase (e.g. edA in  E. coli ); 
     (c) a gene encoding glycoaldehyde reductase (e.g. gene fucO and/or gldA in  E. coli ); 
     (d) a gene encoding glycolate oxidase (e.g., genes glcD, glcE, glcF and glcG in  E. coli ); 
     (e) a gene encoding a repressor of isocitrate lyase (e.g., gene iclR in  E. coli ); and 
     (f) a gene encoding glucose-6-phosphate isomerase (e.g., gene pgi in  E. coli ). 
     Attenuation of gene expression or inhibition of the activity of the enzyme encoded by the gene can be done by introducing mutations into the gene that reduce the activity of the corresponding enzyme or by replacing the natural promoter by a low strength promoter or by using an agent that destabilizes the corresponding messenger RNA or the protein. Attenuation of gene expression or inhibition of the activity of the enzyme encoded by the gene can be done by deleting the corresponding gene from the microorganism using techniques known in the art. 
     In one embodiment, the recombinant microorganism of the present disclosure expresses a set of genes encoding: 
     (a) malate dehydrogenase that catalyzes the conversion of pyruvate to malate; 
     (b) malate thiokinase that catalyzes the conversion of malate to malyl-CoA; and 
     (c) malyl CoA lyase that catalyzes the conversion of malyl-CoA to glyoxylate and acetyl-CoA; 
     (d) optionally phosphoenolpyruvate carboxylase that catalyzes the conversion of PEP to oxaloacetate, and/or phosphoenolpyruvate carboxykinase that catalyzes the conversion of PEP to oxaloacetate, and/or pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate;
 
and comprises at least one modification selected from the group consisting of:
 
(a) deletion or attenuation of a gene encoding malate synthase;
 
(b) deletion or attenuation of a gene encoding isocitrate dehydrogenase;
 
(c) deletion or attenuation of a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(d) deletion or attenuation of a gene encoding malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate or malate to oxaloacetate (malate:quinone oxidoreductase); and
 
(e) deletion or attenuation of a gene encoding pyruvate kinase.
 
     In one embodiment, the recombinant microorganism of the present disclosure expresses a set of genes encoding: 
     (a) phosphoenolpyruvate carboxylase that catalyzes the conversion of PEP to oxaloacetate and/or phosphoenolpyruvate carboxykinase that catalyzes the conversion of PEP to oxaloacetate and/or pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate and/or malate dehydrogenase that catalyzes the conversion of pyruvate to malate;
 
(b) malate thiokinase;
 
(c) malyl CoA lyase; and
 
(d) optionally malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate;
 
and comprises at least one modification selected from the group consisting of:
 
(a) deletion or attenuation of a gene encoding malate synthase;
 
(b) deletion or attenuation of a gene encoding isocitrate dehydrogenase;
 
(c) deletion or attenuation of a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(d) deletion or attenuation of a gene encoding malate dehydrogenase that catalyzes the conversion of malate to pyruvate; and
 
(e) deletion or attenuation of a gene encoding pyruvate kinase.
 
     In another embodiment, the recombinant microorganism comprising the rGS pathway expresses a set of genes encoding: 
     (a) malate dehydrogenase that catalyzes the conversion of pyruvate to malate; 
     (b) malate thiokinase that catalyzes the conversion of malate to malyl-CoA; and 
     (c) malyl-CoA lyase that catalyzes the conversion of malyl-CoA to glyoxylate and acetyl-CoA; 
     (d) optionally phosphoenolpyruvate carboxylase that catalyzes the conversion of PEP to oxaloacetate, and/or phosphoenolpyruvate carboxykinase that catalyzes the conversion of PEP to oxaloacetate, and/or pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate;
 
and comprises at least one modification selected from the group consisting of:
 
(a) deletion or attenuation of a gene encoding malate synthase;
 
(b) deletion or attenuation of a gene encoding isocitrate dehydrogenase;
 
(c) deletion or attenuation of a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(d) deletion or attenuation of the gene encoding malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate or malate to oxaloacetate;
 
(e) deletion or attenuation of a gene encoding pyruvate kinase;
 
(f) deletion or attenuation of a gene encoding glyoxylate carboligase;
 
(g) deletion or attenuation of a gene encoding 2-oxo-4-hydroxyglutarate aldolase;
 
(h) deletion or attenuation of a gene encoding glycoaldehyde reductase;
 
(i) deletion or attenuation of a gene encoding glycolate oxidase; and
 
(j) deletion or attenuation of a gene encoding a repressor of isocitrate lyase.
 
     In one embodiment, the overall stoichiometry of the glycolic acid production using the rGS pathway and/or modifications in one or more of the genes describe above is: Glucose+2 CO 2 →2 GA+2 acetyl-CoA−2 NAD(P)H−2 ATP. In another embodiment, the overall stoichiometry of the glycolic acid production using the rGS pathway and/or modifications in one or more of the genes describe above is: Glucose+2 CO 2 +2 NAD(P)H+2 ATP→4 GA+2 Quinol. 
     Redox balance is important in fine-tuning of metabolic pathways to achieve maximum product yield potential. Imbalance in the redox state, e.g., imbalanced intracellular pool of NADPH and NADH co-factors, imbalanced net ATP, and/or shortage of reducing agents, can result in a lower product yield and generation of undesired by-products. The present disclosure encompasses recombinant microorganisms in which the redox balance is fine-tuned and methods of use thereof. For example, the recombinant microorganisms of any one of the embodiments disclosed herein may comprise genes encoding transhydrogenases and/or NAD kinases to increase the intracellular concentrations of NADH and/or NADPH thereby reaching increased product yield. In an exemplary embodiment, the recombinant microorganisms of any one of the embodiments disclosed herein may comprise genes encoding transhydrogenases such as “pntAB” and/or “udhA” from  E. coli  and/or a gene encoding NAD kinase such as “yfjB” from  E. coli . The expression of these genes can, for example, increase the intracellular concentration of NADPH thereby increasing the activity of NADPH-dependent glyoxylate reductase to facilitate the conversion of glyoxylate to glycolate. 
     The use of transhydrogenases (e.g. gene pntAB and udhA in  E. coli ) and/or NAD kinases (e.g. gene yfjB in  E. coli ) to increase intracellular concentrations of NADH or NADPH has been described in US20140335578, Cui et al., Microbial Cell Factories 2014, 13:21, and Shi et al., Metabolic Engineering 16 (2013)1-10; all of which are incorporated by reference herein. 
     In one embodiment, reducing agents such as sulfur-containing compounds (e.g., sulfites, sulfur dioxide and cystein) and/or hydrogen can be added to the culture medium as an additional reducing power source in order to adjust the redox balance of the metabolic pathway to increase the product yield. In another embodiment, an exogenous source of hydrogen or other additional source of electrons/NAD(P)H may be added to the culture medium for metabolic pathways with negative balance of NADH or NADPH. 
     In certain embodiments, a gene encoding malate: quinone oxidoreductase (also called malate dehydrogenase) is inactivated by deletion or attenuation in the recombinant microorganisms comprising the reverse GS pathway. 
     The rGS pathway of the present disclosure can be combined with known GA and glycine producing pathways. Currently known GA and/or glycine producing pathways include a serine/hydroxypyruvate pathway described in U.S. Pat. No. 8,911,978; a glyoxylate shunt (GS) pathways described in U.S. Pat. Nos. 9,034,615 and 8,945,888, PCT Publication No. WO 2016/193540 and U.S. Pre-Grant Publication No. 2014/0295510; a D-erythrose based pathway described in PCT Publication No. WO 2015/181074; and a pentose derivative to glycolaldehyde based pathways described in PCT Publication Nos. WO 2017/059236 and WO 2016/79440 and U.S. Pre-grant Publication Nos. US 2016/0076061 and US 2015/0147794. All these pathways generate excess NADH and release excess CO 2 , i.e., these pathways do not reach the thermodynamic possible maximum yield. By combining these known GA and glycine producing pathways with the rGS pathway of the present disclosure, the yield of GA and/or glycine can be increased substantially. 
     Yield of GA using some of the previously published pathways: 
     Serine/Hydroxypyruvate Pathways: 
     1 Glucose→→2 GA+2 CO 2 +6 NADH+0 ATP; y=0.84 g/g, 49% of Y(max)=1.70 g/g 
     GS Pathway: 
     Glucose→2 GA+2 CO 2 +4 NADH+2 quinol+2 ATP; y=0.84 g/g, 49% of Y(max)=1.70 g/g 
     Pentose Derivative Pathways, with GS: 
     Xylose→2 GA+1 CO 2 +3 NADH+1 quinol+0 ATP; y=1.01 g/g, 59% of Y(max)=1.71 g/g 
     Erythrose Pathway: 
     Glucose→3 GA+2 NADH+1 quinol−1 ATP, y=1.27 g/g, 75% of Y(max)=1.70 g/g. 
     By combining or co-utilizing the above pathways with the rGS pathway of the present invention, the yield of GA can be substantially increased. For example, in certain embodiments, a co-utilization of the known GA producing pathways with the rGS pathway of the invention could provide increased GA yield as follows: 
     GS and rGS Pathway: 
     Glucose+2/3 CO 2 +2/3 ATP→10/3 GA+2 quinol; y=1.41 g/g, 83% of Y(max)=1.69 g/g 
     GS and rGS Pathway (No Flux on Malate Dehydrogenase): 
     Glucose+2 CO 2 +2 NAD(P)H→4 GA+2 quinol; y=1.69 g/g, 100% of Y(max)=1.69 g/g 
     Pentose Derivative Pathways, with GS and rGS: 
     Xylose+CO 2 +1 ATP→3 GA+1 quinol; y=1.52 g/g, 90% of Y(max)=1.69 g/g 
     Serine, GS and rGS Pathways: 
     Glucose+CO 2 +1.5 ATP→3.5 GA+1.5 quinol; y=1.48 g/g, 88% of Y(max)=1.69 g/g. 
     In one embodiment, the reverse glyoxylate shunt pathway of the present invention utilizes NADH and CO 2  generated by other glycolic acid glycine producing pathways and/or glycoaldehyde generating pathway, and/or CO 2  and/or HCO3 −  and/or other carbon source exogenously provided, thereby increasing the yield potential. For example, in one embodiment, the reverse glyoxylate shunt pathway of the present disclosure utilizes the NADH and CO 2  generated by a serine/hydroxypyruvate-based pathway described in U.S. Pat. No. 8,911,978. In another embodiment, the reverse glyoxylate shunt pathway utilizes the NADH and CO 2  generated by a glyoxylate shunt pathway described in U.S. Pat. Nos. 9,034,615 and 8,945,888, PCT Publication No. WO 2016/193540 and U.S. Pre-Grant Publication No. 2014/0295510. In yet another embodiment, the reverse glyoxylate shunt pathway utilizes the NADH and CO 2  generated by a D-erythrose and pentose derivative to glycoaldehyde based pathways described in a PCT Publication Nos. WO 2015/181074, WO 2017/059236, and WO 2016/79440 and U.S. Pre-grant Publication Nos. US 2016/0076061 and US 2015/0147794. 
     The recombinant microorganisms of the present disclosure include a bacterium, yeast or a fungus. In certain embodiments, the microorganism is selected from, but not limited to, Enterobacteriaceae, Clostridiaceae, Bacillaceae, Streptomycetaceae, Corynebacteriaceae and Saccharomycetaceae. In one embodiment, the microorganism is a species of  Escherichia, Clostridium, Bacillus, Klebsiella, Pantoea, Salmonella, Lactobacillaceae, Corynebacterium  or  Saccharomyces . In one embodiment, the microorganism is  Escherichia coli  or  Corynebacterium glutamicum  or  Clostridium acetobutylicum  or  Bacillus subtilis  or  Saccharomyces cerevisiae.    
     Glycine Production 
     Glyoxylate produced using any one of the pathways described above can be converted to glycine using various enzymes. For example, glycine can be produced from glyoxylate through transamination with alanine, for e.g., by alanine-glyoxylate aminotransferase (EC 2.6.1.44). Usually, natural pathways utilize glutamate as an amino group donor in another transamination reaction to replenish alanine from pyruvate catalyzed by alanine transaminase (EC 2.6.1.2). Glutamate itself can be replenished from the resulting 2-oxoglutarate by fixing the common nitrogen source NH 3  into it, requiring a NAD(P)H glutamate synthase (EC 1.4.1.13, EC 1.4.1.14). The overall stoichiometry is glyoxylate+NH3+1 NAD(P)H→glycine. Other enzymes that can facilitate the conversion of glyoxylate to glycine include glycine dehydrogenase (E.C. 1.4.1.10), glycine transaminase (E.C. 2.6.1.4), serine-glyoxylate transaminase (E.C. 2.6.1.45) and glycine oxidase (E.C. 1.4.3.19). Accordingly, the recombinant microorganism of any one of the embodiments disclosed herein may comprise one or more gene selected from the group consisting of: a gene encoding alanine-glyoxylate aminotransferase (EC 2.6.1.44), a gene encoding glycine dehydrogenase (E.C. 1.4.1.10), a gene encoding glycine transaminase (E.C. 2.6.1.4), a gene encoding serine-glyoxylate transaminase (E.C. 2.6.1.45) and/or a gene encoding glycine oxidase (E.C. 1.4.3.19). 
     In an exemplary embodiment, a gene encoding glycine dehydrogenase (EC 1.4.1.10) can be from  Mycobacterium  sp. (e.g.  Mycobacterium tuberculosis, Mycobacterium smegmatis ),  Pseudomonas  sp.,  Xanthobacter  sp., or  Bacillus  sp. 
     In an exemplary embodiment, a gene encoding glycine transaminase (EC 2.6.1.4): can be from  Rhodopseudomonas palustris, Lactobacillus  sp.,  Hydrogenobacter  sp.,  Rattus  sp., or  Rhodopseudomonas  sp. 
     Yield of glycine using previously published or natural pathways: 
     Glyoxylic Acid Using Glyoxylate Shunt: 
     glucose→2 glyoxylic acid+6 NADH+2 quinol+2 ATP; y=0.82 g/g, 33% of Y(max)=2.51 g/g 
     Glycine Via Glyoxylate Transamination: 
     glucose+2 NH 3 →2 glycine+4 NADH+2 quinol+2 ATP; y=0.701 g/g(glucose+2NH 3 ), 58% of Y(max)=1.20 g/g 
     Glycine Via Serine Decarboxylation: 
     glucose+2 THF+2 NH 3 →2 glycine+2 M-THF+2 NADH+0 ATP; y=0.701 g/g(glucose+2NH 3 ). 
     Yield of glycine by co-utilizing the known pathways with the rGS pathway of the invention: 
     Pentose Derivative Pathways, GS and rGS, Using Glyoxylate Transamination: 
     xylose+3 NH 3 +CO 2 +1 ATP→3 glycine+1 quinol; y=1.12 g/g(xylose+3NH 3 ), 90% of Y(max)=1.25 g/g 
     GS and rGS, Using Glyoxylate Transamination: 
     glucose+10/3 NH 3 +2/3 CO 2 +2/3 ATP→10/3 glycine+2 quinol; y=1.06 g/g(glucose+10/3 NH 3 ), 85% of Y(max)=1.24 g/g 
     GS and rGS, Using Glyoxylate Transamination (No Flux on Malate Dehydrogenase): 
     Glucose+4 NH 3+2  CO 2 +2 NAD(P)H→4 glycine+2 quinol; y=1.24 g/g, 100% of Y(max)=1.24 g/g 
     Serine, GS and rGS Pathways: 
     glucose+3.5 NH 3 +CO 2 +1.5 ATP→3.5 glycine+1.5 quinol; y=1.10 g/g(glucose+3.5NH 3 ), 89% of Y(max)=1.24 g. 
     In one embodiment, the level of expression of at least one gene selected from the group consisting of: 
     (a) a gene encoding alanine-glyoxylate aminotransferase; 
     (b) a gene encoding glycine dehydrogenase; 
     (c) a gene encoding glycine transaminase; 
     (d) a gene encoding serine-glyoxylate transaminase; 
     (e) a gene encoding glycine oxidase; 
     (f) a gene encoding alanine transaminase; and 
     (g) a gene encoding NAD(P)H-dependent glutamate synthase; 
     is increased in the recombinant microorganism comprising the rGS pathway to increase the production of glycine. In another embodiment, one or more of these genes may comprise a gain of function mutation that increases the activity of the enzymes encoded by these genes. 
     The glyoxylate producing recombinant microorganisms of the present invention may also co-produce glycolic acid and glycine. 
     In some embodiments, microorganisms of the present invention do not produce isopropyl alcohol. In one embodiment, microorganisms of the present invention do not produce serine and/or glutamic acid via the reverse glyoxylate shunt pathway. In some embodiments, microorganisms of the present invention may not comprise one or more enzymes that convert glycine to serine. For example, in one embodiment, the microorganisms of the present invention may comprise a loss of function mutation in the gene encoding serine hydroxymethyltransferase. In another embodiment, the microorganisms may not comprise glycine consuming pathways. 
     The microorganisms comprising the reverse glyoxylate pathway show increased production of glycolic acid and glycine. In one embodiment, the microorganisms of the present disclosure lack pathways that convert glycolic acid and/or glycine into other products or intermediates. 
     Co-Utilization of the rGS Pathway with Other Glycolic Acid Producing Pathways 
     In certain embodiments, the recombinant microorganisms comprising the reverse glyoxylate shunt pathway utilizes NADH and CO 2  generated by other glycolate and/or glycine generating pathways and/or other carbon source (CO 2  and/or HCO 3   −  and/or other carbonates) exogenously provided. For example, in one embodiment, the rGS pathway of the present invention can be co-utilized with pentose derivative to glycoaldehyde based pathways described in WO 2017/059236, US 2016/0076061, US 2015/0147794, and WO 2016/079440. 
     Accordingly, in one embodiment, the recombinant microorganism comprising the rGS pathway may further comprise pathways and/or modifications described in these documents. For example, the recombinant microorganism comprising the rGS pathway may have reduced or eliminated activity of, or reduced or eliminated expression of xylulokinase, recombinantly express an enzyme that interconverts xylulose to ribulose, recombinantly expresses D-ribulose-phosphate aldolase (e.g., fucA gene from  E. coli ), recombinantly expresses a D-ribulokinase (e.g., gene fucK from  E. coli ), and/or recombinantly expresses a glycolaldehyde dehydrogenase, such as aldehyde dehydrogenase A (e.g., gene aldA from  E. coli ). 
     The recombinant microorganism comprising the rGS pathway may have reduced or eliminated activity of, or reduced or eliminated expression of xylulokinase, recombinantly express an enzyme to convert D-xylulose to D-xylulose-1P (e.g., khk-C from  Homo sapiens ), recombinantly expresses D-xylulose-1-phosphate aldolase (e.g., gene aldoB from  Homo sapiens ) and recombinantly expresses a glycoaldeyde dehydrogenase, such as aldehyde dehydrogenase A (e.g., gene aldA from  E. coli ). The recombinant microorganism comprising the rGS pathway may have reduced or eliminated activity of, or reduced or eliminated expression of an enzyme that interconverts xylose to D-xylulose (e.g., gene xylA from  E. coli ), recombinantly expresses an enzyme to convert xylose to D-xylonate, recombinantly expresses an enzyme to convert D-xylonate to 2-dehydro-3-deoxy-D-pentonate (DPP) (e.g., gene yagF from  E. coli ), recombinantly expresses a 2-keto-3-deoxy-D-pentonate aldolase (e.g., gene yagE from  E. coli ) and recombinantly expresses a glycoaldeyde dehydrogenase, such as aldehyde dehydrogenase A (e.g., gene aldA from  E. coli ). 
     In some embodiments, the recombinant microorganism comprising the rGS pathway may include a deletion of the gene encoding xylulokinase (e.g., gene xylB from  E. coli ). In some embodiments, the enzyme that interconverts xylulose and ribulose is D-tagatose 3-epimerase (e.g. gene dte from  Pseudomonas cichorii ). In certain embodiments, D-tagatose 3-epimerase is encoded by the dte gene from  P. cichorii  that is codon-optimized for  E. coli  or  S. cerevisiae . In some embodiments, the recombinant microorganism comprising the rGS pathway may have reduced or eliminated activity of, or reduced or eliminated expression of glycolaldehyde reductase. For example, the recombinant microorganism may include a deletion of the gene encoding glycolaldehyde reductase (e.g. gene fucO). 
     In another embodiment, the rGS pathway of the present invention can be co-utilized with a serine/hydroxypyruvate pathway described in U.S. Pat. No. 8,911,978. Accordingly, in one embodiment, the recombinant microorganism comprising the rGS pathway may show an increased level of expression of pyruvate decarboxylase (e.g., pyruvate decarboxylase encoded by genes Pdc1, Pdc 5, Pdc6 from yeast), aldehyde dehydrogenase (e.g., aldehyde dehydrogenase encoded by genes aldA, aldB, aldH, and gabD), serine transaminase, and/or serine oxidase. 
     In another embodiment, the recombinant microorganism comprising the rGS pathway may further comprise genetic modifications described in U.S. Pat. Nos. 9,034,615, and 8,945,888; PCT Publication Nos. WO 2016/193540 and WO 2015/181074; and U.S. Pre-Grant Publication No. 2014/0295510. 
     Methods 
     The present invention provides methods for the production of glycolic acid and glycine using any one of the recombinant microorganisms described herein. 
     In one embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate, a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A. The gene encoding malate dehydrogenase may encode for malate dehydrogenase that catalyzes the conversion of pyruvate to malate and/or OAA to malate but preferably does not catalyze (or catalyzes less efficiently) the reverse reaction from malate to pyruvate or malate to OAA. 
     In one embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA in combination with a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A. 
     In one embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA in combination with a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine. In the same embodiment, the recombinant microorganism that may have, or may not have, a glucose-6-phosphate isomerase, pyruvate kinase, pyruvate dehydrogenase and/or malate dehydrogenase enzymes down-regulated or deleted. 
     In one embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA in combination with a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate, a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A. The gene encoding malate dehydrogenase may encode for malate dehydrogenase that catalyzes the conversion of pyruvate to malate and/or OAA to malate but preferably does not catalyze (or catalyzes less efficiently) the reverse reaction from malate to pyruvate or malate to OAA. 
     In another embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate; a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A. In one embodiment, the gene encoding malate dehydrogenase encodes for a modified malate dehydrogenase that catalyzes the conversion of pyruvate to malate or OAA to malate but does not catalyze the reverse reaction of malate to pyruvate or malate to OAA or shows reduced conversion of malate to pyruvate or malate to OAA. 
     In another embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A, wherein the microorganism does not comprise a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate or comprises a deletion or loss-of-function mutation in the gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate. 
     In another embodiment, the method comprises culturing in a suitable culture medium a recombinant microorganism that expresses a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA; a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A, and a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl coenzyme A, wherein the microorganism does not comprise a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate or comprises a loss-of-function mutation in the gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate. 
     In one embodiment, glyoxylate is reduced to glycolate by the NAD(P)H-dependent glyoxylate reductase expressed by the recombinant microorganisms. 
     In one embodiment, glyoxylate is converted to glycine using alanine-glyoxylate aminotransferase; glycine dehydrogenase; glycine transaminase; serine-glyoxylate transaminase; and/or glycine oxidase expressed by the recombinant microorganisms. 
     A suitable culture medium used in the methods of the present disclosure comprises a fermentable carbon source. In one embodiment, the carbon source is selected from sugars, glycerol, alcohols, organic acids, alkanes, fatty acids, lignocellulose, proteins, carbon dioxide, and carbon monoxide. In an exemplary embodiment, the carbon source is sugar. In a further exemplary embodiment, the carbon source is a hexose and/or a pentose sugar. In another embodiment, the carbon source is glucose or oligomers of glucose, or comprises a biomass hydrolysate comprising hemicellulose. In another embodiment, the carbon source is a monosaccharide (such as glucose, xylose, arabinose, fructose, and mannose), a disaccharide (such as sucrose, lactose, and maltose), an oligosaccharide (such as galactose) or a polysaccharide (such as cellulose). 
     In another embodiment, the method for producing GA and/or glycine comprises culturing in a suitable culture medium a recombinant microorganism that expresses a set of genes encoding: 
     (a) malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate; 
     (b) malate thiokinase that catalyzes the conversion of malate to malyl-CoA; and 
     (c) malyl CoA lyase that catalyzes the split of malyl-CoA into glyoxylate and acetyl-CoA; 
     (d) optionally phosphoenolpyruvate carboxylase, and/or phosphoenolpyruvate carboxykinase, and/or pyruvate carboxylase; 
     and comprises at least one modification selected from the group consisting of: 
     (a) deletion or attenuation of a gene encoding malate synthase; 
     (b) deletion or attenuation of a gene encoding isocitrate dehydrogenase; 
     (c) deletion or attenuation of a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase; 
     (d) deletion or attenuation of a gene encoding malate dehydrogenase that converts oxaloacetate to malate or malate to oxaloacetate; and 
     (e) deletion or attenuation of a gene encoding pyruvate kinase. 
     In another embodiment, the method for producing GA and/or glycine comprises culturing in a suitable culture medium a recombinant microorganism that expresses a set of genes encoding: 
     (a) malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate; 
     (b) malate thiokinase that catalyzes the conversion of malate to malyl-CoA; and 
     (c) malyl CoA lyase that catalyzes the split of malyl-CoA into glyoxylate and acetyl-CoA; 
     and comprises: 
     (a) an attenuation of the gene encoding malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate or the gene encoding malate dehydrogenase that catalyzes malate to oxaloacetate or an attenuation/mutation of the gene encoding malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate so it shows reduced conversion of malate to pyruvate; and
 
(b) deletion or attenuation of a gene encoding malate synthase (e.g. genes aceB and/or glcB in  E. coli  or genes DAL7 and MLS1 in  S. cerevisiae ).
 
     In another embodiment, the method for producing GA and/or glycine comprises culturing in a suitable culture medium a recombinant microorganism that expresses a set of genes encoding: 
     (a) phosphoenolpyruvate carboxylase that catalyzes the carboxylation of PEP to oxaloacetate and/or phosphoenolpyruvate carboxykinase that catalyzes the carboxylation of PEP to oxaloacetate and/or pyruvate carboxylase that catalyzes the carboxylation of pyruvate to oxaloacetate and/or malate dehydrogenase that catalyzes the carboxylation or pyruvate to malate;
 
(b) malate thiokinase that catalyzes the conversion of malate to malyl-CoA; and
 
(c) malyl-CoA lyase that catalyzes the conversion of malyl-CoA to glyoxylate and acetyl-CoA;
 
(d) and optionally malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate, and;
 
wherein the microorganism comprises at least one modification selected from the group consisting of:
 
(a) deletion or attenuation of a gene encoding malate synthase;
 
(b) deletion or attenuation of a gene encoding isocitrate dehydrogenase;
 
(c) deletion or attenuation of a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(d) deletion or attenuation of the gene encoding malate dehydrogenase that catalyzes the conversion of malate to pyruvate or the gene encoding malate dehydrogenase that catalyzes the conversion of malate to oxaloacetate;
 
(e) deletion or attenuation of a gene encoding pyruvate kinase
 
(f) deletion or attenuation of a gene encoding glyoxylate carboligase;
 
(g) deletion or attenuation of a gene encoding 2-oxo-4-hydroxyglutarate aldolase;
 
(h) deletion or attenuation of a gene encoding glycoaldehyde reductase;
 
(i) deletion or attenuation of a gene encoding glycolate oxidase; and
 
(j) deletion or attenuation of a gene encoding a repressor of isocitrate lyase.
 
     In yet another embodiment, the method for producing GA and/or glycine comprises culturing in a suitable culture medium a recombinant microorganism that shows an increased level of expression or increased activity (i.e., enhanced kinetic parameters for the desired reaction) or higher specificity (i.e., engineered enzyme that is &gt;5×, &gt;10 1 ×, &gt;10 2 ×, &gt;10 3 ×, 10 4 × or preferably &gt;10 5  more specific to the target substrate compared to its wild-type enzyme; or novel homologous enzyme) of one or more enzymes selected from the group consisting of: pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate thiokinase, malyl coenzyme A lyase, NADH-dependent glyoxylate reductase, and NADPH-dependent glyoxylate reductase. 
     In yet another embodiment, the method for producing GA and/or glycine comprises culturing in a suitable culture medium a recombinant microorganism that shows a decreased level of expression of at least one enzyme selected from the group consisting of: malate synthase, isocitrate dehydrogenase, pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase, pyruvate kinase, glyoxylate carboligase, 2-oxo-4-hydroxyglutarate aldolase, glucose-6-phosphate isomerase, glycoaldehyde reductase, and glycolate oxidase. 
     In another embodiment, the method for producing GA and/or glycine may comprise a deletion or modification that decreases the activity of the pyruvate dehydrogenase, preventing or at least diminishing a major carbon loss from pyruvate conversion to acetyl-CoA, and favoring the carbon rerouting from pyruvate or phosphoenolpyruvate into oxaloacetate via carboxylation activity of enzyme candidates proposed herein. 
     In another embodiment, the method for producing GA and/or glycine may comprise a deletion or modification that decreases the activity of the pyruvate kinase, favoring the carbon fixation of phosphoenolpyruvate into oxaloacetate via carboxylation activity of enzyme candidates proposed herein. 
     The methods of the present disclosure may provide a yield of glycolic acid in the range of about 1.1 g of glycolic acid per g of carbon source to about 2.0 g/g, including values and ranges therebetween. For example, the yield of glycolic acid can be about 1.1., 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or about 2.0 g/g. The yield of glycolic acid may range from about 1.1 to about 1.8 g/g, about 1.2 to about 1.8 g/g, about 1.3 to about 1.8 g/g, about 1.4 to 1.8 g/g, about 1.4 to 1.7 g/g, or about 1.4 to 1.6 g/g. 
     The methods of the present disclosure may provide a yield of glycine in the range of about 1.0 g of glycine per g of carbon source to about 1.5 g/g, including values and ranges therebetween. For example, the yield of glycine can be about 1.0, 1.1., 1.2, 1.3, 1.4, or 1.5 g/g. The yield of glycine may range from about 1.0 to about 1.4 g/g, about 1.0 to about 1.3 g/g, about 1.0 to about 1.2 g/g, about 1.1 to 1.5 g/g, about 1.1 to 1.4 g/g, or about 1.1 to 1.3 g/g, or about 1.2 to 1.4 g/g. 
     Production of Poly-Glycolic Acid (PGA) 
     The present disclosure also encompasses methods of producing polyglycolic acid (PGA). The glycolic acid produced by the recombinant microorganisms of the present disclosure can be used for the production of PGA. PGA can be produced from GA via in vivo polymerization reactions or via chemical polymerization reactions. 
     In one embodiment, PGA is produced using an in vivo polymerization route described in U.S. Pre-Grant Publication No. 2011/0118434A1, incorporated by reference in its entirety. In this route, once GA is produced, two classes of enzymes—Coenzyme A transferase/synthase and PHA synthase, may be used to produce PGA inside the cell. Accordingly, in one embodiment, the recombinant microorganism of any one of the embodiments disclosed herein may comprise a gene encoding polyhydroxyalkanoate (PHA) synthase. 
     Four major classes of PHA synthases are known (Rhem, B., 2003). Class I and Class II PHA synthases comprise enzymes consisting of only one type of subunit (PhaC). According to their in vivo and in vitro specificity, class I PHA synthases (e.g. in  Ralstonia eutropha ) preferentially utilize CoA-thioester of various hydroxy fatty acids comprising 3 to 5 carbons atoms, whereas class II PHA synthases (e.g. in  Pseudomonas aeruginosa ) preferentially utilize CoA-thioester of various hydroxy fatty acids comprising 6 to 14 carbon atoms. Class III synthases (e.g. in  Allochromatium vinosum ) comprises enzymes consisting of two different types of subunits: the PhaC and the PhaE subunits. These PHA synthases prefer CoA-thioesters of hydroxy fatty acids comprising 3 to 5 carbons atoms. Class IV PHA synthases (e.g. in  Bacillus megaterium ) resemble the class III PHA synthases, but PhaE is replaced by PhaR. 
     In one embodiment, the gene encoding the PHA synthase is phaC, phaEC and/or phaCR. 
     In one embodiment, glycolic acid is converted into glycolyl-coA by one or more enzymes selected from the group consisting of: acyl-CoA synthetases, acyl-CoA transferases, and phosphotransbutyrylase associated to butyrate kinase. 
     In an exemplary embodiment, the enzyme transforming the glycolic acid into glycolyl-CoA is from an Enterobacteriaceae species. In an exemplary embodiment, the recombinant microorganism of any one of the embodiments described herein may comprise the gene prpE encoding propionyl coenzyme A synthetase from  Escherichia coli  or  Salmonella thyphimurium , the gene acs from  E. coli  encoding acetyl-CoA transferase, the gene ptb encoding phosphotransbutyrylase and/or the gene buk encoding butyrate kinase. 
     If not through in vivo polymerization, there are chemical polymerization methods known in the Art: Ring opening polymerization from Kureha to have a high-molecular weight PGA (paper is attached) as well as direct polycondensation that reaches to a low-molecular weight PGA (Singh &amp; Tiwari, 2010.). 
     Alternatively, the PGA can be prepared via chemical polymerization routes such as the ring-opening polymerization of cyclic diesters or the polycondensation of 2-hydroxycarboxylic acids. In an exemplary embodiment, the PGA can be produced using the ring opening polymerization method described by Yamane et al. (Polymer Journal, August 2014, pp. 1-7) to obtain a high-molecular weight PGA. In another exemplary embodiment, the PGA can be produced via direct polycondensation to obtain a low-molecular weight PGA (Singh &amp; Tiwari, International Journal of Polymer Science, Volume 2010, Article ID 652719, 23 pages, doi:10.1155/2010/652719). 
     The present disclosure also provides methods for producing recombinant microorganisms capable of producing glycolic acid and/or glycine from glyoxylate using a reverse glyoxylate shunt. In one embodiment, the method for producing a recombinant microorganism comprises introducing into the microorganism one or more genes or introducing a gain-of-function mutation into one or more genes selected from the group consisting of: 
     (a) a gene encoding pyruvate carboxylase to convert pyruvate to OAA; 
     (b) a gene encoding phosphoenolpyruvate carboxylase to convert phosphoenolpyruvate to OAA; 
     (c) a gene encoding phosphoenolpyruvate carboxykinase to convert phosphoenolpyruvate to OAA; 
     (d) a gene encoding malate dehydrogenase to convert OAA to malate and/or pyruvate to malate; 
     (e) a gene encoding malate thiokinase to convert malate to malyl coenzyme A; 
     (f) a gene encoding malyl coenzyme A lyase to convert malyl coenzyme A to glyoxylate and acetyl-CoA; 
     (g) a gene encoding NADH-dependent glyoxylate reductase to convert glyoxylate to glycolate; and 
     (h) a gene encoding NADPH-dependent glyoxylate reductase to convert glyoxylate to glycolate. 
     The nucleotide sequences for the genes encoding the above polypeptides are known in the art and are publicly available (www.ncbi.nlm.nih.gov/genbank/). Methods for incorporating a desired nucleic acid sequence into the genome of the microorganism or into an expression vector are also known. For example, U.S. Pat. No. 9,034,615, which is incorporated by reference herein, discloses a method for incorporating the gene ycdW (encoding NADPH-dependent glyoxylate reductase) into an expression vector. 
     In certain embodiments, the recombinant microorganism comprises a deletion or modification that attenuates the expression of an endogenous gene. Exemplary methods for producing these microorganisms include deleting the gene or attenuating the expression of the gene by replacing the natural promoter by a low strength promoter or by introducing mutations into the gene that lead to decreased enzymatic activity. 
     In some embodiments, the method for producing a recombinant microorganism comprises introducing into the microorganism a deletion or modification that attenuates the expression of or inhibits the activity of the enzyme encoded by at least one endogenous gene selected from the group consisting of: 
     (a) a gene encoding malate synthase; 
     (b) a gene encoding isocitrate dehydrogenase; 
     (c) a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase; 
     (d) a gene encoding pyruvate kinase; 
     (e) a gene encoding malate dehydrogenase; 
     (f) a gene encoding glyoxylate carboligase; 
     (g) a gene encoding 2-oxo-4-hydroxyglutarate aldolase; 
     (h) a gene encoding glycoaldehyde reductase; 
     (i) a gene encoding glycolate oxidase; 
     (j) a gene encoding a repressor of isocitrate lyase; and 
     (l) a gene encoding a glucose-6-phosphate isomerase. 
     The methods for producing a recombinant microorganism may further comprise (a) introducing into the microorganism a deletion or modification that attenuates the expression of a gene encoding malate: quinone oxidoreductase and/or (b) introducing a gain-of-function mutation into a gene encoding malate dehydrogenase, a gene encoding pyruvate carboxylase, a gene encoding phosphoenolpyruvate carboxylase, a gene encoding phosphoenolpyruvate carboxykinase, a gene encoding malate thiokinase, a gene encoding malyl-CoA lyase a gene encoding alanine-glyoxylate aminotransferase; a gene glycine dehydrogenase; a gene encoding glycine transaminase; a gene encoding serine-glyoxylate transaminase; a gene encoding glycine oxidase; a gene encoding alanine transaminase and/or a gene encoding NADPH-dependent glutamate synthase. 
     The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art. 
     While the disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains and as may be applied to the essential features hereinbefore set forth and as follows in the scope of the appended claims. 
     EXAMPLES 
     Example 1 
     In Silico Analysis for the Biosynthesis and Improvement of Glycolic Acid Production Via Reverse Glyoxylate Shunt Activity in  E. coli    
     Flux balance analyses (FBAs) were performed to simulate the impact of the genetic modifications as described herein, on the production yield of glycolate under various scenarios ( FIG. 3  and  FIG. 4 ). To do so, genome-scale metabolic model iJO1366, containing all known metabolic reactions of  Escherichia coli  (Orth J D. et al. (2011) A comprehensive genome-scale reconstruction of  Escherichia coli  metabolism—2011. Mol Syst Biol. 7:535), was modified to simulate glycolic acid (GA) production using a combination of glyoxylate (GS) and reverse glyoxylate (rGS) shunts. The model was modified to include additional reactions and the corresponding metabolites, including a malate thiokinase reaction (EC 6.2.1.9), a malyl-coA ligase reaction (EC 4.1.3.24), and a pyruvate carboxylase reaction (EC 6.4.1.1). 
     Simulations were carried out using the OptFlux software (Rocha L. (2010) OptFlux: an open-source software platform for in silico metabolic engineering. BMC Syst Biol. 4:45). In exemplary embodiments, parsimonious flux balance analyses were performed to evaluate the maximal theoretical production yields of GA through GS/rGS engineering. Depending on the exemplary embodiment, the transport system used was either hexokinase HXK (E.C. 2.7.1.1) or phosphotransferase system (PTS), while the carboxylation enzyme used to enter the TCA cycle was either phosphoenolpyruvate carboxykinase (PEPCK) (E.C. 4.1.1.32), phosphoenolpyruvate carboxylase (PPC) (E.C. 4.1.1.31), or pyruvate carboxylase PPC (EC 6.4.1.1). 
     Simulations were performed by applying a set of constraints readily reproduced under in vivo culture conditions of an  E. coli  strain, in which glucose is a carbon substrate and under aerobic conditions. The glucose substrate flux was arbitrarily set at 10 Cpmoles.gCDW-1.h-1. No constraints were set regarding a minimal biomass yield, or cell maintenance cost. Simulation results depicting the maximal theoretical production of GA are presented in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Simulation results depicting the maximal theoretical production of GA. 
               
            
           
           
               
               
            
               
                   
                 Theoretical 
               
               
                   
                 production 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 qSubstrates 
                 qProducts 
                 yield 
               
               
                 Glucose 
                 Carboxylation 
                 (μmole · gCDW−1 · h−1) 
                 (μmole · gCDW−1 · h−1) 
                 (gGA/ 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Transport 
                 Reaction 
                 Glucose 
                 O2 
                 CO2 
                 Glycolate 
                 Pyruvate 
                 Acetate 
                 gGlucose) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 HXK 
                 PEPCK 
                 10 
                 8.57 
                 8.57 
                 34.29 
                 0 
                 0 
                 1.43 
               
               
                   
                 PPC 
                 10 
                 10.3 
                 6.06 
                 32.12 
                 0.61 
                 0 
                 1.34 
               
               
                   
                 PYC 
                 10 
                 10.3 
                 6.06 
                 32.12 
                 0.61 
                 0 
                 1.34 
               
               
                 PTS 
                 PEPCK 
                 10 
                 5 
                 10 
                 20 
                 10 
                 0 
                 0.83 
               
               
                   
                 PPC 
                 10 
                 5 
                 10 
                 20 
                 10 
                 0 
                 0.83 
               
               
                   
                 PYC 
                 10 
                 10.09 
                 6.44 
                 33.04 
                 0.004 
                 0.17 
                 1.38 
               
               
                   
               
            
           
         
       
     
     Simulated flux maps are depicted in  FIG. 3  and  FIG. 4 . Simulations show that a theoretical production yield of GA from glucose, via GS/rGS, can reach between 0.83 and 1.43 g GA /g Glucose , depending on the glucose transport system and the carboxylation enzyme used. Strains relying on PEPCK or PPC as a carboxylation enzyme are less performant in a PTS+ strain. This is likely due to the competition between the PTS system and PEPCK/PPC for their common substrate, phosphoenolpyruvate. The performance of said strains can however be enhanced in a PTS deficient strain, where glucose is mostly transported via hexokinase HXK. As depicted on the flux maps ( FIG. 3  and  FIG. 4 ), maximal yields can only be achieved by diverting 86 to 100% of the carbon flux coming from glucose towards the pentose phosphate pathway, to provide the redox cofactors for the final glyoxylate reductase reaction (E.C. 1.1.1.26). This carbon flow towards the pentose phosphate pathway was considered as an alternative to provide the NADPH cofactor requirement for a NADPH-dependent glyoxylate reductase. 
     Example 2 
     In Vive Biosynthesis and Improvement of Glycolic Acid Production Via Reverse Glyoxylate Shunt Activity in  E. coli , Combined with Carboxylation Through Pyruvate Carboxylase Activity 
     As previously described (Alkim C. (2016) The synthetic xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures. Biotechnol Biofuels, 9:201), production of glycolic acid (GA) in  E. coli  can be enhanced by inactivating all annotated reactions that consume glyoxylic acid, i.e., malate synthase, encoded by aceB (GenBank Gene ID: 948512) and glcB (GenBank Gene ID: 948857), glyoxylate carboligase, encoded by gcl (GenBank Gene ID: 945394), and 2-oxo-4-hydroxyglutarate aldolase, encoded by eda (GenBank Gene ID: 946367). Reoxidation of GA can further be prevented by deleting the glycolate oxidase-encoding glcDEFG operon (GenBank Gene ID: 947353, 2847718, 2847717, 947473). 
     The experiments described below were thus carried out in an  Escherichia coli  K12 strain MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda. The strain, referred to as SGK_rGS_00, was a gift from Alkim et al. (Alkim C. (2016) The synthetic xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures. Biotechnol Biofuels, 9:201). 
     Deletion of the Pgi Locus, Encoding for Phosphoglucose Isomerase 
     To construct a strain with an enhanced pentose phosphate activity and NADPH pool, deletion of pgi (GenBank Gene ID: 948535), encoding for glucose-6-phosphate isomerase, was performed by CRISPR-Cas9 according to standard procedure (Jiang Y. et al. (2015) Multigene editing in the  Escherichia coli  genome via the CRISPR-Cas9 system. Appl Environ Microbiol, 81:2506-2514). Plasmids pTargetF (pMB1 aadA sgRNA-cadA) harboring a guide RNA, and pCas (repA101-Ts kan Pcas-cas9 ParaB-Red lacIq Ptrc-sgRNA-pMB1) harboring a cas9 gene and a 1-Red recombinase, were obtained from AddGene (respectively, Addgene plasmid #62226 and #62225; Addgene, Cambridge, USA). 
     A pTargetF pMB1 aadA sgRNA-pgi, expressing a guide RNA with a N20 sequence targeting the pgi locus, was obtained by overlap PCR, using primers Pgi_N20_FW, and Pgi_N20_RV described in Table 2. The donor DNA/disruption cassette was supplied as a PCR fragment, obtained by amplifying and combining 500 bp upstream and downstream the pgi locus by overlap PCR, using primers Pgi_H1_FW, Pgi_H1_RV, Pgi_H2_FW and Pgi_H2_RV (see Table 2). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Oligonucleotides used for pgi disruption using CRISPR-Cas9. Binding 
               
               
                 regions are underlined. N20 sequence specific for pgi is indicated 
               
               
                 in italics. 
               
            
           
           
               
               
            
               
                 Primer Name 
                 Sequence 
               
               
                   
               
               
                 Pgi_N20_FW 
                 GTCCTAGGTATAATACTAGT CCGATTATCTGGGGTGAACC   GTTTTAGAGCTAGAAATAGC   
               
               
                   
                 (SEQ ID NO: 1) 
               
               
                   
               
               
                 Pgi_N20_RV 
                   ACTAGTATTATACCTAGGACTGAG  (SEQ ID NO: 2) 
               
               
                   
               
               
                 Pgi_H1_FW 
                   ATGAAAAACATCAATCCAACGC  (SEQ ID NO: 3) 
               
               
                   
               
               
                 Pgi_H1_RV 
                 GGTGGATCAG TCGGTCACCATGTATGGGC  (SEQ ID NO: 4) 
               
               
                   
               
               
                 Pgi_H2_FW 
                 TGGTGACCGA CTGATCCACCAGGGAACCA  (SEQ ID NO: 5) 
               
               
                   
               
               
                 Pgi_H2_RV 
                   CATATCGACGATGATTAACCGC  (SEQ ID NO: 6 
               
               
                   
               
            
           
         
       
     
     Genome editing was performed by adapting the protocol from (Jiang Y. et al. (2015) Multigene editing in the  Escherichia coli  genome via the CRISPR-Cas9 system. Appl Environ Microbiol, 81:2506-2514). Strain SGK_rGS_00 was first transformed by electroporation with the pCAS plasmid using standard procedure (Woodall C A. (2003) Plasmid Vectors. Methods in Molecular Biology. 235). Competent cells of the strain SGK_rGS_00 harboring pCAS were prepared while inducing λ-Red recombinase with arabinose (10 mM final concentration), as described previously (Jiang Y. et al. (2015) Multigene editing in the  Escherichia coli  genome via the CRISPR-Cas9 system. Appl Environ Microbiol, 81:2506-2514). 50 μl of competent cells was thereafter mixed with 100 ng of pTargetF plasmid, and 400 ng of donor DNA. Electroporation was performed in a 2-mm electroporation cuvette (VWR) at 2.5 kV, and the product was suspended immediately in 1 ml of LB medium (pre-warmed at 30° C.). Cells were allowed to recover at 30° C. overnight, before being plated onto LB agar containing kanamycin (50 μg/ml) and spectinomycin (50 μg/ml), and were incubated overnight at 30° C. Transformants were identified by colony PCR and sequencing. The resulting strain was called SGK_rGS_01: MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi. 
     Deletion of the aceE Locus, Encoding for Subunit E1 of the Pyruvate Dehydrogenase 
     To construct a strain that accumulates pyruvate to enhance the use of a carboxylation enzyme such as pyruvate carboxylase to enter the Krebs cycle, deletion of pyruvate dehydrogenase subunit E1 aceE was performed in strain SGK_rGS_01 according to standard procedure (Thomasson L C. (2007)  E. coli  Genome Manipulation by P1 Transduction. Curr Protoc Mol Biol. 79:1.17), using a MG1655 Δpgi::KanR strain JW0110, obtained from the Keio single-gene deletion collection (Baba T. et al. (2006) Construction of  Escherichia coli  K-12 in-frame, single-gene knockout mutants: the Keio collection. Mol Syst Biol. 2:2006.0008). Transformants were selected on LB agar supplemented with 100 μg/ml kanamycin and identified by colony PCR and sequencing. Removal of the antibiotic marker was further performed by specific recombination of FTR regions, using Flp recombination, as previously described in the literature (Datsenko K A. et al. (2000) One-step inactivation of chromosomal genes in  Escherichia coli  K-12 using PCR products. Proc Natl Acad Sci USA. 97(12):6640-5). The resulting strain was called SGK_rGS_02: MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔaceE. 
     Expression of Pyruvate Carboxylase, Citrate Synthase, Isocitrate Lyase and Glyoxylate Reductase to Enhance Carbon Fixation, Glyoxylate Shunt Activity and Glycolic Acid Synthesis 
     Pyruvate carboxylase from  Rhizobium etli  strain CFN42 (SEQ ID NO: 20) (Uniprot accession number: Q2K340) was synthesized by Genewiz® (Leipzig, Germany). Native isocitrate lyase aceA (SEQ ID NO: 21) (GeneBank Gene ID: 948517) and glyoxylate reductase ghrA (SEQ ID NO: 23) (GeneBank Gene ID: 946431) genes were amplified by PCR from the genome of  E. coli  MG1655 using primers in Table 3. A NADH-insensitive citrate synthase mutant gltA R163L  (SEQ ID NO: 22) was recovered by PCR from plasmid pACT3w-ppc K620S -gltA R163L , as described in Trichez et al. (Trichez D. (2018) Engineering of  Escherichia coli  for Krebs cycle-dependent production of malic acid. Microb Cell Fact. 17:113). 
     To express these genes as a synthetic operon, a pZS13-Luc plasmid (Expressys) was first modified by replacing the P AllacO-1  promoter by a J23119 constitutive promoter (SEQ ID NO: 19) (http://parts.igem.org/Promoters/Catalog/Anderson) and introducing a multiple cloning site. The J23119 promoter was obtained as a synthetic gene fragment, synthesized by GeneWiz® (Leipzig, Germany). It was subsequently cloned into a pZS13-Luc plasmid by restriction cloning, between restriction sites AatII and KpnI. A multiple cloning site was recovered by digestion with KpnI and AvrII from a pZA21-MCS plasmid (Expressys), and incorporated into the plasmid by restriction cloning between said restriction sites KpnI and AvrII. The resulting plasmid is referred to as pZS1-J23119-MCS. 
     All genes were amplified by PCR using the primers described in Table 3. PCR fragments were purified on gel using EZ-10 Spin Column DNA Gel Extraction Kit (BioBasic) according to the manufacturer&#39;s protocol. Purified fragments were subsequently cloned into pZS1-J23119-MCS plasmid linearized by restriction with KpnI and HindIII, by using the NEBuilder® HiFi DNA Assembly Cloning Kit (New England Biolabs) according to the manufacturer&#39;s protocol. Construction was confirmed by PCR and sequencing. The resulting synthetic operon is referred to as J23119-pyc-aceA-gltA R163L -ghrA (SEQ ID NO: 24), and the plasmid as pZS1-pyc. (see Table 4). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Oligonucleotides used for the construction of the synthetic operon 
               
               
                 J23119-pyc-aceA-gltAR164L-ghrA. Binding regions are underlined. 
               
               
                 Overhangs are used for assembly cloning using NEBuilder ® HiFi 
               
               
                 DNA Assembly Cloning Kit (New England Biolabs). 
               
            
           
           
               
               
            
               
                 Primer Name 
                 Sequence 
               
               
                   
               
               
                 pyc_FW 
                 TTGTTTAACTTTAAGGAGGTTTGGA GGTACCATGCCCATATCCAAG  (SEQ 
               
               
                   
                 ID NO: 7) 
               
               
                   
               
               
                 pyc_RV 
                 TTTTCATACGGTTCCTCCTTCTAGA TCATCCGCCGTAAACCG  (SEQ ID NO: 
               
               
                   
                 8) 
               
               
                   
               
               
                 aceA_FW 
                 CGGATGATCTAGAAGGAGGAACCGT ATGAAAACCCGTACACAACAAAT   
               
               
                   
                 (SEQ ID NO: 9) 
               
               
                   
               
               
                 aceA_RV 
                 TTGTATCAGCCATCGTGTGCCTCCT TTAGAACTGCGATTCTTCAGTG  (SEQ 
               
               
                   
                 ID NO: 10) 
               
               
                   
               
               
                 gltA_FW 
                 ATCGCAGTTCTAAAGGAGGCACACG ATGGCTGATACAAAAGCAAAACTC   
               
               
                   
                 (SEQ ID NO: 11) 
               
               
                   
               
               
                 gltA_RV 
                 AGATGATATCCATCGTGTGCCTCCT TTAACGCTTGATATCGCTTTTAAAGTC   
               
               
                   
                 (SEQ ID NO: 12) 
               
               
                   
               
               
                 ghrA_FW 
                 TATCAAGCGTTAAAGGAGGCACACG ATGGATATCATCTTTTATCACCCAAC   
               
               
                   
                 (SEQ ID NO: 13) 
               
               
                   
               
               
                 ghrA_RV 
                 GGCTGCAGGAATTCGATATCATAGA TTAGTAGCCGCGTGCGCG  (SEQ ID 
               
               
                   
                 NO: 14) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Oligonucleotides used for the construction of the synthetic 
               
               
                 operon PTac-sucCD-mcl. Binding regions are underlined. 
               
               
                 Overhangs are used for assembly cloning using NEBuilder ® HiFi 
               
               
                 DNA Assembly Cloning Kit (New England Biolabs). 
               
            
           
           
               
               
            
               
                 Primer Name 
                 Sequence 
               
               
                   
               
               
                 sucCD_FW 
                 ACAATTTCACACAGGAAACA GAATTCCTATAATTTTGTTTAACTTTAAG   
               
               
                   
                 (SEQ ID NO: 15) 
               
               
                   
               
               
                 sucCD_RV 
                 TATAG TCTAGATCAGAATCTGATTCCGTG  (SEQ ID NO: 16) 
               
               
                   
               
               
                 mcl_FW 
                 GAATCAGATTCTGATCTAGA CTATAATTTTGTTTAACTTTAAGGAGGTT   
               
               
                   
                 (SEQ ID NO: 17) 
               
               
                   
               
               
                 mcl_RV 
                 TAGCACGCGT TTACTTTCCGCCCATCGCG  (SEQ ID NO: 18) 
               
               
                   
               
            
           
         
       
     
     Expression of Malate Thiokinase and Malyl-coA Ligase to Introduce Reverse Glyoxylate Shunt Activity 
     The sucC2-sucD2 operon from  Methylococcus capsulatus  str. Bath (SEQ ID NO: 26) (Uniprot Q607L9 and Q607L8), encoding a malate thiokinase, and mcl gene from  Methylobacterium extorquens  AM1 (SEQ ID NO: 27) (Uniprot C5B113), encoding a malyl-coA lyase, were ordered as synthetic genes from GeneWiz® (Leipzig, Germany). To express these genes as a synthetic operon, a pZA31-MCS plasmid (Expressys) was first modified by replacing the P LtetO-1  promoter by a P Tac  inducible promoter (SEQ ID NO: 25), recovered from a standard pACT3 plasmid, and cloned by restriction cloning between restriction sites AatII and KpnI. The resulting plasmid is referred to as pZA3-P Tac -MCS. 
     All genes were amplified by PCR using the primers described in Table 4. PCR fragments were purified on gel using EZ-10 Spin Column DNA Gel Extraction Kit (BioBasic) according to the manufacturer&#39;s protocol. Purified fragments were subsequently cloned as a synthetic operon into pZA3-P Tac -MCS plasmid linearized by restriction with EcoRI and MluI, by using the NEBuilder® HiFi DNA Assembly Cloning Kit (New England Biolabs) according to the manufacturer&#39;s protocol. Construction was confirmed by PCR and sequencing. The resulting synthetic operon is referred to as P Tac -sucCD-mcl (SEQ ID NO: 28), and the plasmid as pZA3-rGS (see Table 5). 
     Assay for Glycolic Acid Production 
     Three  E. coli  strains were tested for the GA production assay. Wild-type strain MG1655, and engineered strains SGK_rGS_01 and SGK_rGS_02 were tested (i) without plasmids, as negative controls (ii) with plasmid pZS1-pyc only, (ii) with plasmid pZA3-rGS, (iv) with both plasmids. All strains were transformed by electroporation with the corresponding plasmids using standard procedure (Woodall C A. (2003) Plasmid Vectors. Methods in Molecular Biology. 235). Genotypes of plasmids and strains are presented in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Genotypes of plasmids and strains for the glycolic acid production assay. 
               
            
           
           
               
               
               
            
               
                 Category 
                 Name 
                 Genotype 
               
               
                   
               
               
                 Plasmids 
                 pZS1-pyc 
                 pZS1-J23119-pyc-aceA-gltA R163L -ghrA (SEQ ID NO: 24) 
               
               
                   
                 pZA3-rGS 
                 pZA3-P Tac -sucCD-mcl 
               
               
                 Strains 
                 MG1655 
                 K12, F − , lambda − , rph-1 
               
               
                   
                 MG1655_pyc 
                 K12, F − , lambda − , rph-1 + pZS1-pyc 
               
               
                   
                 MG1655_rGS 
                 K12, F − , lambda − , rph-1 + pZA3-rGS 
               
               
                   
                 MG1655_pyc_rGS 
                 K12, F − , lambda − , rph-1 + pZS1-pyc + pZA3-rGS 
               
               
                   
                 SGK_rGS_01 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi 
               
               
                   
                 SGK_rGS_01_pyc 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi + pZS1-pyc 
               
               
                   
                 SGK_rGS_01_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi + pZA3-rGS 
               
               
                   
                 SGK_rGS_01_pyc_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi + pZS1-pyc + 
               
               
                   
                   
                 pZA3-rGS 
               
               
                   
                 SGK_rGS_02 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔaceE 
               
               
                   
                 SGK_rGS_02_pyc 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔaceE + pZS1- 
               
               
                   
                   
                 pyc 
               
               
                   
                 SGK_rGS_02_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔaceE + pZA3- 
               
               
                   
                   
                 rGS 
               
               
                   
                 SGK_rGS_02_pyc_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔaceE + pZS1- 
               
               
                   
                   
                 pyc + pZA3-rGS 
               
               
                   
               
            
           
         
       
     
     Strains were grown in M9 glucose medium (20 g/L glucose) supplemented with 15 mM acetate and 1 g/L Casamino acid for about 50 hours. Ampicillin and chloramphenicol were added with a final concentration of 100 μg/mL and 25 μg/mL, respectively (i.e. ampicillin for strain harboring pZS1-pyc, and chloramphenicol for strains harboring pZA3-rGS). Cultures were induced with IPTG (0.5 mM final) when their OD600 reaches around 0.6-0.8. Growth was monitored by OD 600 . Samples were taken during growth until stationary phase. Glucose consumption and metabolite production was then analyzed by HPLC-UV/RI (Dionex Ultimate 3000, Thermo Fisher Scientific), with a Rezex ROA-Organic Acid column (Phenomenex), at 80° C. with H 2 SO 4  0.5 mM as mobile phase (0.5 mL/min). GA titer and GA yield after 24H are presented in Table 6. 
     As shown in Table 6, no significant production of glycolic acid was detected in the MG1655 wild-type control strain, without plasmid or with plasmid pZS1-pyc or pZA3-RGS only. This was expected, as all major competitive pathway (i.e. glyoxylate and glycolate degradation pathways) are still active in the wild-type strain. Interestingly, a limited amount of GA could however be detected when expressing both the pZS1-pyc plasmid, and the pZA3-rGS in the MG1655 wild-type strain. Titer reached up to 0.11 g/L of GA, which is a first indication that the combination of GS/rGS pathway has a positive impact on the production of GA, even in the wild-type strain. 
     Regarding engineered strain SGK_rGS_01, no significant GA production could be detected in the empty control strain, or in the strain with pZA3-rGS only. GA production could however be detected up to a titer of ca. 0.18 g/L when enhancing the glyoxylate shunt activity and glyoxylate reductase activity, using plasmid pZS1-pyc. The addition of the pZA3-rGS plasmid in the strain improved the GA titer by 910%, reaching up to 1.91 g/L. The production yield reached up to 0.24 g GA /g glucose  after 22.5 hours, showing a 2400% improvement when compared to the production yield without the rGS engineering 
     Regarding engineered strain SGK_rGS_02, no significant GA production could be detected in the control strain with single plasmid. GA production was only detected when combining both plasmids, up to a titer of ca. 0.28 g/L. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 GA titer and yield evaluated during glycolic acid production assay after 24 h of growth 
               
            
           
           
               
               
               
               
            
               
                   
                 MG1655 
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 With 
                 SGK_rGS_01 
                 SGK_rGS_02 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 pZS1- 
                   
                   
                   
                 With 
                   
                   
                   
                 With 
               
               
                   
                   
                 With 
                 With 
                 pyc + 
                   
                 With 
                 With 
                 pZS1-pyc + 
                   
                 With 
                 With 
                 pZS1-pyc + 
               
               
                   
                 Empty 
                 pZS1- 
                 pZA3- 
                 pZA3- 
                 Empty 
                 pZS1- 
                 pZA3- 
                 pZA3- 
                 Empty 
                 pZS1- 
                 pZA3- 
                 pZA3- 
               
               
                   
                 (control) 
                 pyc 
                 rGS 
                 rGS 
                 (control) 
                 pyc 
                 rGS 
                 rGS 
                 (control) 
                 pyc 
                 rGS 
                 rGS 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 GA titer (g/L) 
                 0 
                 0 
                 0 
                 0.11 
                 0 
                 0.18 
                 0 
                 1.91 
                 0 
                 0 
                 0 
                 0.28 
               
               
                 GA yield 
                 0 
                 0 
                 0 
                 0.01 
                 0 
                 0.01 
                 0 
                 0.24 
                 0 
                 0 
                 0 
                 0.025 
               
               
                 (gGA/gGlucose) 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Biosynthesis and Improvement of Glycolic Acid Production Via Reverse Glyoxylate Shunt Activity in  E. coli  Combined with Carboxylation Through Pep Carboxylase Activity 
     The experiments described below were carried out in an  Escherichia coli  K12 strain MG1655 ΔaceB ΔglcDEFGB Δgcl/Δedd-eda. The strain, referred to as SGK_rGS_00, was a gift from Alkim et al. (Alkim C. et al. (2016) The Synthetic Xylulose-1 phosphate pathway increases production of glycolic acid from xylose-rich sugar mixtures. Biotechnol Biofuels, 9:201). 
     Deletion of the Pgi Locus, Encoding for Phosphoglucose Isomerase 
     To construct a strain with an enhanced pentose phosphate activity and NADPH pool, deletion of pgi (GenBank Gene ID: 948535), encoding for glucose-6-phosphate isomerase, was performed by CRISPR-Cas9 according to standard procedure (Jiang Y. et al. (2015) Multigene editing in the  Escherichia coli  genome via the CRISPR-Cas9 system. Appl Environ Microbiol, 81:2506-2514). Disruption of the strain was performed as previously described in Example 2, and is referred to as SGK_rGS_01 (Table 5). 
     Deletion of the pykF Locus, Encoding for Pyruvate Kinase I 
     To construct a strain that accumulates phosphoenol pyruvate to enhance the use of a carboxylation enzyme such as pep carboxylase to enter the Krebs cycle, deletion of pyruvate kinase I pykF (GenBank Gene ID: 946179) was performed in strain SGK_rGS_01 by transduction according to standard procedure (Thomasson L C. (2007)  E. coli  Genome Manipulation by P1 Transduction. Curr Protoc Mol Biol. 79:1.17), using a MG1655 Δpgi::KanR strain JW1666, obtained from the Keio single-gene deletion collection (Baba T. et al. (2006) Construction of  Escherichia coli  K-12 in-frame, single-gene knockout mutants: the Keio collection. Mol Syst Biol. 2:2006.0008). Transformants were selected on LB agar supplemented with 100 μg/ml kanamycin and identified by colony PCR and sequencing. Removal of the antibiotic marker was further performed by specific recombination of FTR regions, using Flp recombination, as previously described in the literature (Datsenko K A. et al. (2000) One-step inactivation of chromosomal genes in  Escherichia coli  K-12 using PCR products. Proc Natl Acad Sci USA. 97(12):6640-5). The resulting strain was called SGK_rGS_03 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔpykF. 
     Expression of pep carboxylase, citrate synthase, isocitrate lyase and glyoxylate reductase to enhance carbon fixation, glyoxylate shunt activity and glycolic acid synthesis 
     Plasmid pACT3w-ppc K620S -gltA R163L  was obtained from Trichez et al. (Trichez D. (2018) Engineering of  Escherichia coli  for Krebs cycle-dependent production of malic acid. Microb Cell Fact. 17:113). It contains a malate-insensitive pep carboxylase mutant ppc K620S  and a NADH-insensitive citrate synthase mutant gltA R163L , under the control of an inducible P Tac  promoter. It was further modified as described below and used as a backbone to construct a synthetic operon. Genes encoding for the native isocitrate lyase aceA (GeneBank Gene ID: 948517) and the glyoxylate reductase ghrA (GeneBank Gene ID: 946431) were amplified by PCR from the genome of  E. coli  MG1655, respectively using the primers aceA_FW/aceA_RV and ghrA_FW/ghrA_RV described in Table 7. Geneppc K620S  (SEQ ID NO: 29) was amplified by PCR along with plasmid backbone pACT3, using plasmid pACT3w-ppc K620S -gtA R163L  as a template, and primers pACT3_FW/ppc_RV, described in Table 7. Finally, gene gltA R163L  was amplified by PCR, using plasmid pACT3w-ppc K620S -gltA R1163L  as template, and primers gltA_FW/gltA_RV described in Table 7. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Oligonucleotides used for the construction of the synthetic operon 
               
               
                 J23119-pyc-aceA-gltAR164L-ghrA. Binding regions are underlined. 
               
               
                 Overhangs are used for assembly cloning using NEBuilder ® HiFi 
               
               
                 DNA Assembly Cloning Kit (New England Biolabs). 
               
            
           
           
               
               
            
               
                 Primer name 
                 Sequence 
               
               
                   
               
               
                 pACT3_FW 
                   TCTAGAAAGCTTCTGTTTTGGC  (SEQ ID NO: 31) 
               
               
                   
               
               
                 ppc_RV 
                   GTTCCTCCTTCTAGATTAGCCG  (SEQ ID NO: 32) 
               
               
                   
               
               
                 aceA_FW 
                 CGGCTAATCTAGAAGGAGGAACCGT ATGAAAACCCGTACACAACAAAT  (SEQ ID 
               
               
                   
                 NO: 33) 
               
               
                   
               
               
                 aceA_RV 
                 TTGTATCAGCCATCGTGTGCCTCCT TTAGAACTGCGATTCTTCAGTG  (SEQ ID NO: 
               
               
                   
                 34) 
               
               
                   
               
               
                 gltA_FW 
                 ATCGCAGTTCTAAAGGAGGCACACG ATGGCTGATACAAAAGCAAAACTC  (SEQ ID 
               
               
                   
                 NO: 35) 
               
               
                   
               
               
                 gltA_RV 
                 AGATGATATCCATCGTGTGCCTCCT TTAACGCTTGATATCGCTTTTAAAGTC  (SEQ ID 
               
               
                   
                 NO: 36) 
               
               
                   
               
               
                 ghrA_FW 
                 TATCAAGCGTTAAAGGAGGCACACG ATGGATATCATCTTTTATCACCCAAC  (SEQ ID 
               
               
                   
                 NO: 37) 
               
               
                   
               
               
                 ghrA_RV 
                 TCCGCCAAAACAGAAGCTTTCTAGA TTAGTAGCCGCGTGCGCG  (SEQ ID NO: 38) 
               
               
                   
               
            
           
         
       
     
     PCR fragments were purified on gel using EZ-10 Spin Column DNA Gel Extraction Kit (BioBasic) according to the manufacturer&#39;s protocol. Purified fragments were subsequently assembled, by using the NEBuilder® HiFi DNA Assembly Cloning Kit (New England Biolabs) according to the manufacturer&#39;s protocol. Construction was confirmed by PCR and sequencing. The resulting synthetic operon is referred to as P tac -ppc K620S -aceA-gtA R163L -ghrA (SEQ ID NO: 30), and the plasmid as pACT3-ppc. 
     Expression of Malate Thiokinase and Malyl-coA Ligase to Introduce Reverse Glyoxylate Shunt Activity 
     As described in Example 2, the sucC2-sucD2 operon from  Methylococcus capsulatus  str. Bath (SEQ ID NO: 26) (Uniprot Q607L9 and Q607L8), encoding a malate thiokinase, and mcl gene from  Methylobacterium extorquens  AM1 (Uniprot C5B113), encoding a malyl-coA lyase, were ordered as synthetic genes from GeneWiz® (Leipzig, Germany). Plasmid pZA3-rGS, containing the synthetic operon P Tac -sucCD-mcl (SEQ ID NO: 28), was obtained as described in Example 2. In order to express the P Tac -sucCD-mcl in a background compatible with plasmid pACT3-ppc, it was further transferred into a pZE23-MCS plasmid (Expressys), by restriction cloning between restriction sites AvrII and BglII. The resulting plasmid is referred to as pZE2-rGS. 
     Assay for Glycolic Acid Production 
     Two strains were tested for the GA production assay. Wild-type MG1655 and engineered strain SGK_rGS_03 were tested (i) with plasmid pACT3-ppc only, (ii) with plasmid pZE2-rGS only, and (iii) with both plasmids. All strains were transformed by electroporation with the corresponding plasmids using standard procedure (Woodall C A. (2003) Plasmid Vectors. Methods in Molecular Biology, 235). Genotypes of plasmids and strains are presented in Table 8. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Genotypes of plasmids and strains used for glycolic acid production assay. 
               
            
           
           
               
               
               
            
               
                 Category 
                 Name 
                 Genotype 
               
               
                   
               
               
                 Plasmids 
                 pACT3-ppc 
                 pZS1-J23119-pyc-aceA-gltA R163L -ghrA 
               
               
                   
                 pZE3-rGS 
                 pZE2-P Tac -sucCD-mcl 
               
               
                 Strains 
                 MG1655_ppc 
                 K12, F − , lambda − , rph-1 + pACT3-ppc 
               
               
                   
                 MG1655_rGS 
                 K12, F − , lambda − , rph-1+ pZE2-rGS 
               
               
                   
                 MG1655_ppc_rGS 
                 K12, F − , lambda − , rph-1+ pZE2-rGS 
               
               
                 Strains 
                 SGK_rGS_03_ppc 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔpykF + pACT3- 
               
               
                   
                   
                 PPC 
               
               
                   
                 SGK_rGS_03_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔpykF + pZE2-rGS 
               
               
                   
                 SGK_rGS_03_ppc_rGS 
                 MG1655 ΔaceB ΔglcDEFGB Δgcl Δedd-eda Δpgi ΔpykF + pZE2-rGS 
               
               
                   
               
            
           
         
       
     
     Strains were grown in M9 glucose medium (20 g/L glucose) supplemented with 15 mM acetate and 1 g/L Casamino acid for about 50 hours. Chloramphenicol and kanamycin were added with a final concentration of 25 μg/mL and 50 μg/mL, respectively (i.e. chloramphenicol for strain harboring pACT3-ppc, and kanamycin for strains harboring pZE2-rGS). Cultures were induced with IPTG (0.5 mM final) when their OD600 reaches around 0.6-0.8. Growth was monitored by OD 600 . Samples were taken during growth until stationary phase. Glucose consumption and metabolite production was then analyzed by HPLC-UV/RI (Dionex Ultimate 3000, Thermo Fisher Scientific), with a Rezex ROA-Organic Acid column (Phenomenex), at 80° C. with H 2 SO 4  0.5 mM as mobile phase (0.5 mL/min). Glucose titer, GA titer and GA yield are presented in Table 9. 
     As shown in Table 9, a production of GA could be detected in the wild-type control, when expressing the pACT3-ppc with and without pZE2-rGS, but only with a maximal yield of 0.02 g GA /g glucose ; whereas no production of glycolic acid was measured in the SGK_rGS_03 strain with plasmid pZE2-rGS only. GA production could, however, be detected in this strain up to a titer of about 0.8 g/L when enhancing the carbon fixation, glyoxylate shunt activity and glyoxylate reductase activity, using plasmid pACT3-ppc. The addition of the pZE2-rGS plasmid in SGK_rGS_03 does not improve the GA titer. The production yield reached up to 0.21 g GA /g glucose  after 46 hours, showing a 525% improvement with the strain expressing pACT3-ppc, and a 1050% improvement with the wild-type strain expressing both plasmids. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 GA titer and yield evaluated during glycolic acid production assay after 46 h. 
               
            
           
           
               
               
               
            
               
                   
                 MG1655 
                 SGK_rGS_03 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 With 
                   
                   
                   
                 With 
               
               
                   
                   
                 With 
                 With 
                 pACT3- 
                   
                 With 
                 With 
                 pACT3- 
               
               
                   
                 Empty 
                 pACT3- 
                 pZE2- 
                 ppc + 
                 Empty 
                 pACT3- 
                 pZE2- 
                 ppc + 
               
               
                   
                 (control) 
                 ppc 
                 rGS 
                 pZE2-rGS 
                 (control) 
                 ppc 
                 rGS 
                 pZE2-rGS 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 GA titer (g/L) 
                 0 
                 0.35 
                 0 
                 0.2 
                 ND 
                 0.8 
                 0 
                 0.71 
               
               
                 GA yield 
                 0 
                 0.02 
                 0 
                 0.02 
                 ND 
                 0.04 
                 0 
                 0.21 
               
               
                 (gGA/gGlucose) 
               
               
                   
               
            
           
         
       
     
     Enumerated Embodiments 
     1. A glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, comprising: 
     (a) a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate; 
     (b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and 
     (c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA. 
     2. A glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, comprising: 
     (a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA;
 
(b) a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate;
 
(c) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and
 
(d) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine.
 
3. A glyoxylate producing recombinant microorganism for the synthesis of glycolic acid (GA) and/or glycine, comprising:
 
(a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA;
 
(b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and
 
(c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the recombinant microorganism does not catalyze the conversion of oxaloacetate to malate.
 
4. The recombinant microorganism of any preceding embodiment, wherein the recombinant microorganism does not produce isopropyl alcohol, ethanol, acetone, citric acid, itaconic acid, acetic acid, butyric acid, (poly-)3-hydroxybutyric acid, 3-hydroxyisobutyric acid, 3-aminoisobutyric acid, 2-hydroxyisobutyric acid, methacrylic acid, (poly)glutamic acid, glutamic acid, arginine, ornithine, citrulline, leucine, isoleucine, or proline via the acetyl-CoA produced by the malyl coenzyme A lyase.
 
5. The recombinant microorganism of any preceding embodiment, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine.
 
6. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a mutation in the gene encoding malate dehydrogenase, wherein the mutation results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate, malate to pyruvate and/or malate to oxaloacetate.
 
7. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a gene encoding NADH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate or a gene encoding NADPH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate.
 
8. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase to catalyze the conversion of glyoxylate to glycine.
 
9. The recombinant microorganism of any preceding embodiment, wherein the malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate is from the Enzyme Classification (E.C.) 1.1.1.38, E.C. 1.1.1.39, or E.C. 1.1.1.40.
 
10. The recombinant microorganism of any preceding embodiment, wherein the malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate is from the Enzyme Classification (E.C.) 1.1.1.37.
 
11. The recombinant microorganism of any preceding embodiment, wherein the gene encoding the malate dehydrogenase that catalyzes the carboxylation of pyruvate to malate is selected from the group consisting of: maeA, maeB, dme, mez, mae1, nad-me1, and nad-me2 or homologs thereof.
 
12. The recombinant microorganism of any preceding embodiment, wherein the gene maeA is from  E. coli, Pseudomonas , or  Bacillus ; the gene maeB is from  E. coli  or  Salmonella ; the gene dme is from  Rhizobium ; the gene mez is from  Mycobacterium ; the gene mae1 is from  S. cerevisiae ; and the gene nad-me1 or nad-me2 is from  Arabidopsis thaliana.  
 
13. The recombinant microorganism of any preceding embodiment, wherein the gene maeA is from  B. subtilis ; the gene dme is from  R. melilote ; or the gene mez is from  Mycobacterium tuberculosis.  
 
14. The recombinant microorganism of any preceding embodiment, wherein the gene encoding the malate dehydrogenase that catalyzes the conversion of oxaloacetate to malate is selected from the group consisting of: gene mdh from  E. coli, Corynebacterium, Streptomyces, Saccharomyces  and  Arabidopsis  or homologs thereof.
 
15. The recombinant microorganism of any preceding embodiment, wherein the gene mdh is from  S. coelicolor  or gene mdh1/2/3 from  S. cerevisiae.  
 
16. The recombinant microorganism of any preceding embodiment, wherein the gene encoding malate thiokinase is sucCD and/or SucCD-2 and/or mtkAB from  Methylobacterium  sp.,  Methylobacterium extorquens, Escherichia coli, Thermus thermophiles, Hyphomicrobium  sp.,  Methanocaldococcus jannaschii, Methanothermobacter thermautotrophicus, Rhizobium, Methylococcus capsulatus  or  Pseudomonas ; or homologs thereof.
 
17. The recombinant microorganism of any preceding embodiment, wherein the gene encoding malyl coenzyme A lyase is mcl and/or Mcl1 and/or mclA from  Methylobacterium extorquens, Rhodobacter sphaeroides, Streptomyces, Chloroflexus aurantiacus, Nitrosomonas europaea, Methylococcus capsulans, Nereida ignava, Hyphomicrobium methylovorum, Thalassobius activus, Roseobacter litoralis, Hyphomicrobium denitrificans, R. sphaeroides, Mycobacterium smegmatis  or  Rhodococcus fascians ; or homologs thereof.
 
18. The recombinant microorganism of any preceding embodiment, wherein the gene encoding pyruvate carboxylase is pyc from  Rhizobium etli , PYC1 or PYC2 from yeast or pyc from  B. subtilis ; or homologs thereof.
 
19. The recombinant microorganism of any preceding embodiment, wherein the gene encoding phosphoenolpyruvate carboxylase is ppc from  E. coli , ppc or pepC from  R. marinus , ppcA from  M. thermautotrophicus , pep1 from  Z. mays , ppc1/2/3 from  A. thaliana , ppc from  G. max  or is from  Rhodothermus, Corynebacterium, Salmonella, Hyphomicrobium, Streptococcus, Streptomyces, Pantoea, Bacillus, Clostridium, Pseudomonas, Rhodopseudomonas, Nicotiana tabacum, Amaranthus hypochondriacus, Triticum aestivum  or  Medicago sativa ; or homologs thereof.
 
20. The recombinant microorganism of any preceding embodiment, wherein the gene encoding phosphoenolpyruvate carboxykinase is pck or pckA from  Escherichia coli , pckA from  Selenomonas ruminantium , pckA from  Salmonella typhimurium , pckA from  Klebsiella  sp., pckA from  Thermus  sp, pck or pckA from  Ruminococcus albus  or  Ruminococcus flavefaciens , pckA from  Actinobacillus succinogenes , pck or pckA from  Streptococcus bovis , or is from  Bacillus, Ruminiclostridium thermocellum, Klebsiella, Mycobacterium ; or homologs thereof.
 
21. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises:
 
(a) a gene encoding citrate synthase to convert OAA and acetyl-coA produced by the malyl-coA lyase to citrate;
 
(b) a gene encoding citrate hydro-lyase to convert citrate to cis-aconitate;
 
(c) a gene encoding D-threo-isocitrate hydro-lyase or aconitase to convert cis-aconitate to isocitrate;
 
(d) a gene encoding isocitrate lyase to convert isocitrate to succinate and glyoxylate;
 
(e) a gene encoding succinate dehydrogenase to convert succinate to fumarate; and
 
(f) a gene encoding fumarase to convert fumarate to malate.
 
22. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a loss of function mutation or deletion of the gene encoding malate synthase.
 
23. The recombinant microorganism of any preceding embodiment, wherein the gene encoding glyoxylate reductase activity is selected from the group consisting of: ycdW and/or yiaE from  E. coli , GOR1 from  S. cerevisiae , gyaR from  Thermococcus litoralis  and/or GLYR1 from  A. thaliana.  
 
24. The recombinant microorganism of any preceding embodiment, wherein the pyruvate carboxylase that converts pyruvate to OAA is from the Enzyme Classification System No. E.C. 6.4.1.1; the phosphoenolpyruvate carboxylase that converts phosphoenolpyruvate to OAA is from the E.C. 4.1.1.31; the phosphoenolpyruvate carboxykinase that converts phosphoenolpyruvate to OAA is from the E.C. 4.1.1.32 and E.C. 4.1.1.49.
 
25. The recombinant microorganism of any preceding embodiment, wherein the malate thiokinase that converts malate to malyl coenzyme A is from the Enzyme Classification System No. E.C. 6.2.1.4, E.C. 6.2.1.5, E.C. 6.2.1.9, or E.C. 6.2.1.-; and/or the malyl coenzyme A lyase that converts malyl coenzyme A to glyoxylate and acetyl-CoA is from the E.C. 4.3.1.24 or E.C. 4.3.1.25.
 
26. The recombinant microorganism of any preceding embodiment, wherein one or more genes are expressed heterologously.
 
27. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a deletion or modification that decreases the activity of one or more endogenous genes selected from the group consisting of:
 
(a) a gene encoding isocitrate dehydrogenase;
 
(b) a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(c) a gene encoding pyruvate kinase, and
 
(d) a gene encoding glycolate oxidase.
 
28. The recombinant microorganism of any preceding embodiment, wherein the gene encoding malate synthase is aceB and/or glcB from  E. coli  or DAL7 and/or MLS1 from yeast.
 
29. The recombinant microorganism of any preceding embodiment, wherein the gene encoding isocitrate dehydrogenase is icd from  E. coli  or IDP2 and/or IDH1/2 from yeast.
 
30. The recombinant microorganism of any preceding embodiment, wherein the gene encoding pyruvate dehydrogenase is aceE and/or aceF from  E. coli.  
 
31. The recombinant microorganism of any preceding embodiment, wherein the gene encoding pyruvate kinase is pykA and/or pykF from  E. coli.  
 
32. The recombinant microorganism of any preceding embodiment, wherein the gene encoding glycolate oxidase is glcD, glcE, glcF, and/or glcG from  E. coli.  
 
33. The recombinant microorganism of any preceding embodiment, wherein the yeast is  S. cerevisiae.  
 
34. The recombinant microorganism of any preceding embodiment, wherein the microorganism comprises a deletion or modification that decreases the activity of one or more endogenous genes selected from the group consisting of:
 
(a) a gene encoding glyoxylate carboligase;
 
(b) a gene encoding 2-oxo-4-hydroxyglutarate aldolase;
 
(c) a gene encoding glycoaldehyde reductase; and
 
(d) a gene encoding a repressor of isocitrate lyase.
 
35. The recombinant microorganism of any preceding embodiment, wherein the gene encoding glyoxylate carboligase is gcl; the gene encoding 2-oxo-4-hydroxyglutarate aldolase is edA; the gene encoding glycoaldehyde reductase is fucO and/or gldA; and the gene encoding the repressor of isocitrate lyase is iclR.
 
36. The recombinant microorganism of any preceding embodiment, wherein the level of expression of a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase is increased.
 
37. The recombinant microorganism of any preceding embodiment, wherein the level of expression of a gene encoding alanine transaminase and/or a gene encoding NADPH-dependent glutamate synthase is increased.
 
38. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes NADH and CO 2  generated by other glycolic acid and/or glycine producing pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
39. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes exogenously added CO 2 , a carbonate, and/or a reducing agent in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
40. The recombinant microorganism of any preceding embodiment, wherein the reducing agent is hydrogen, electrons, and/or NAD(P)H.
 
41. The recombinant microorganism of any preceding embodiment, wherein the reducing agent comes from an external source.
 
42. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes NADH and CO 2  generated by a serine/hydroxypyruvate-based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
43. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes NADH and CO 2  generated by a glyoxylate shunt pathway in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
44. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes NADH and CO 2  generated by a D-erythrose to glycoaldehyde based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
45. The recombinant microorganism of any preceding embodiment, wherein the microorganism utilizes NADH and CO 2  generated by a pentose derivative to glycoaldehyde based pathways in the reactions catalyzed by malate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate thiokinase, and malyl coenzyme A lyase.
 
46. The recombinant microorganism of any preceding embodiment, wherein the microorganism is selected from the group consisting of bacterium, yeast, and fungus.
 
47. The recombinant microorganism of any preceding embodiment, wherein the microorganism is a bacterium selected from the group consisting of Enterobacteriaceae, Clostridiaceae, Bacillaceae, Streptomycetaceae, and Corynebacteriaceae.
 
48. The recombinant microorganism of any preceding embodiment, wherein the microorganism is a species of  Escherichia, Clostridium, Bacillus, Klebsiella, Pantoea, Salmonella, Lactobacillus , or  Corynebacterium.  
 
49. The recombinant microorganism of any preceding embodiment, wherein the microorganism is  Escherichia coli  or  Corynebacterium glutamicum  or  Clostridium acetobutylicum  or  Bacillus subtilis.  
 
50. The recombinant microorganism of any preceding embodiment, wherein the microorganism is a yeast selected from the family Saccharomycetaceae.
 
51. The recombinant microorganism of any preceding embodiment, wherein the microorganism is a species of  Saccharomyces.  
 
52. The recombinant microorganism of any preceding embodiment, wherein the microorganism is  Saccharomyces cerevisiae.  
 
53. The recombinant microorganism of any preceding embodiment, wherein the synthesis of glycolic acid and/or glycine is increased by increasing the level of expression or the activity or the specificity of at least one enzyme selected from the group consisting of: pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate thiokinase, malyl coenzyme A lyase, alanine-glyoxylate aminotransferase, glycine dehydrogenase, glycine transaminase, serine-glyoxylate transaminase, glycine oxidase, NADH-dependent glyoxylate reductase, and NADPH-dependent glyoxylate reductase.
 
54. The recombinant microorganism of any preceding embodiment, wherein the synthesis of glycolic acid and/or glycine is increased by decreasing the level of expression or the activity or the specificity of at least one enzyme selected from the group consisting of: malate synthase, isocitrate dehydrogenase, pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase, pyruvate kinase, glucose-6-phosphate isomerase, glyoxylate carboligase, 2-oxo-4-hydroxyglutarate aldolase, glycoaldehyde reductase, and glycolate oxidase.
 
55. The recombinant microorganism of any preceding embodiment, wherein the synthesis of glycolic acid and/or glycine is increased by decreasing the level of expression of a gene encoding a repressor of isocitrate lyase.
 
56. A method of producing glycolic acid and/or glycine using a recombinant microorganism of any preceding embodiment, wherein the method comprises cultivating the recombinant microorganism in a culture medium containing a feedstock providing a carbon source until the glycolic acid and/or glycine are produced.
 
57. The method of any preceding embodiment, wherein the carbon source is selected from the group consisting of: sugars, glycerol, alcohols, organic acids, alkanes, fatty acids, hemicellulose, lignocellulose, proteins, carbon dioxide, and carbon monoxide.
 
58. The method of any preceding embodiment, wherein the carbon source is a hexose and/or pentose sugar.
 
59. The method of any preceding embodiment, wherein the carbon source is glucose.
 
60. The method of any preceding embodiment, wherein the carbon source is sucrose.
 
61. The method of any preceding embodiment, wherein the carbon source comprises a biomass hydrolysate comprising hemicellulose.
 
62. The method of any preceding embodiment, wherein the carbon source is CO 2  or carbonate.
 
63. The method of any preceding embodiment, wherein the carbonate is HCO 3   − .
 
64. A method of producing a recombinant microorganism that produces glycolic acid and/or glycine from glyoxylate, comprising introducing into the microorganism:
 
(a) a gene encoding malate dehydrogenase that catalyzes the conversion of pyruvate to malate;
 
(b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and
 
(c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA.
 
65. A method of producing a recombinant microorganism that produces glycolic acid and/or glycine from glyoxylate, comprising introducing into the microorganism:
 
(a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or
 
a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA;
 
(b) a gene encoding malate dehydrogenase that catalyzes the conversion of OAA to malate;
 
(c) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and
 
(d) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the acetyl-CoA produced by the malyl coenzyme A lyase combines with the OAA to increase the biosynthesis of GA and/or glycine.
 
66. A method of producing a recombinant microorganism that produces glycolic acid and/or glycine from glyoxylate, comprising introducing into the microorganism:
 
(a) a gene encoding pyruvate carboxylase that catalyzes the conversion of pyruvate to oxaloacetate (OAA), and/or a gene encoding phosphoenolpyruvate carboxylase that catalyzes the conversion of phosphoenolpyruvate to OAA, and/or a gene encoding phosphoenolpyruvate carboxykinase that catalyzes the conversion of phosphoenolpyruvate to OAA;
 
(b) a gene encoding malate thiokinase that catalyzes the conversion of malate to malyl coenzyme A; and
 
(c) a gene encoding malyl coenzyme A lyase that catalyzes the conversion of malyl coenzyme A to glyoxylate and acetyl-CoA, wherein the recombinant microorganism does not catalyze the conversion of oxaloacetate to malate.
 
67. The method of any preceding embodiment, wherein the gene encoding malate dehydrogenase comprises a mutation that results in a partial or complete inhibition of the malate dehydrogenase activity that catalyzes the conversion of oxaloacetate to malate, malate to pyruvate or malate to oxaloacetate.
 
68. The method of any preceding embodiment, comprising introducing into the microorganism;
 
(a) a gene encoding NADH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate;
 
(b) a gene encoding NADPH-dependent glyoxylate reductase that catalyzes the conversion of glyoxylate to glycolate; or
 
(i) a gene encoding alanine-glyoxylate aminotransferase, a gene encoding glycine dehydrogenase, a gene encoding glycine transaminase, a gene encoding serine-glyoxylate transaminase, and/or a gene encoding glycine oxidase that catalyzes the conversion of glyoxylate to glycine.
 
69. The method of any preceding embodiment, comprising introducing into the microorganism a loss of function mutation or deletion of the gene encoding malate synthase.
 
70. The method of any preceding embodiment, comprising introducing into the microorganism a deletion or modification that reduces the activity of one or more enzymes encoded by the genes selected from the group consisting of:
 
(a) a gene encoding isocitrate dehydrogenase;
 
(b) a gene encoding pyruvate dehydrogenase, pyruvate oxidase and/or pyruvate formate-lyase;
 
(c) a gene encoding pyruvate kinase;
 
(d) a gene encoding glycolate oxidase; and
 
(e) a gene encoding glucose-6-phosphate isomerase.
 
71. The method of any preceding embodiment, comprising introducing into the microorganism a deletion or modification that reduces the activity of one or more enzymes encoded by the genes selected from the group consisting of:
 
(a) a gene encoding glyoxylate carboligase;
 
(b) a gene encoding 2-oxo-4-hydroxyglutarate aldolase;
 
(c) a gene encoding glycoaldehyde reductase; and
 
(d) a gene encoding a repressor of isocitrate lyase.
 
72. The method of any preceding embodiment, comprising introducing a gain of function mutation into the gene encoding alanine-glyoxylate aminotransferase, the gene encoding alanine-glyoxylate aminotransferase glyoxylate to glycine, the gene encoding glycine dehydrogenase, the gene encoding glycine transaminase, the gene encoding serine-glyoxylate transaminase, and/or the gene encoding glycine oxidase that catalyze the conversion of glyoxylate to glycine.
 
73. The method of any preceding embodiment, comprising introducing a gain of function mutation into a gene encoding alanine transaminase and/or a gene encoding NADPH-dependent glutamate synthase.
 
74. The method of any preceding embodiment, wherein the recombinant microorganism is selected from the group consisting of bacterium, yeast, and fungus.
 
75. The method of any preceding embodiment, wherein the recombinant microorganism is a bacterium selected from the group consisting of Enterobacteriaceae, Clostridiaceae, Bacillaceae, Streptomycetaceae, and Corynebacteriaceae.
 
76. The method of any preceding embodiment, wherein the recombinant microorganism is a species of  Escherichia, Clostridium, Bacillus. Klebsiella, Pantoea, Salmonella, Lactobacillus , or  Corynebacterium.  
 
77. The method of any preceding embodiment, wherein the recombinant microorganism is  Escherichia coli  or  Corynebacterium glutamicum  or  Clostridium acetobutylicum  or  Bacillus subtilis.  
 
78. The method of any preceding embodiment, wherein the recombinant microorganism is a yeast selected from the family Saccharomycetaceae.
 
79. The method of any preceding embodiment, wherein the recombinant microorganism is a species of  Saccharomyces.  
 
80. The method of any preceding embodiment, wherein the recombinant microorganism is  Saccharomyces cerevisiae.  
 
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     However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.