Strategies for optimizing acetyl-CoA formation from glucose in bacteria

Industrial production of acetyl-CoA derivatives, especially commercial chemicals, depends on low feedstock costs. Enhancing acetyl-CoA synthesis from feedstocks such as glucose is essential for reducing the production costs of these end products. Reasonable use of carbon-saving pathways can maximize the production yield and rate of acetyl-CoA while lowering CO2 emission and oxygen dependency. The balance between reducing equivalents and energy must be well designed, especially for anaerobic processes. Fine-tuning the carbon flux between carbon-saving pathways and other pathways via metabolic engineering strategies is not only essential for redox and power balancing but also impels cells to fully utilize the feedstock to maximize the yield of acetyl-CoA and other end products. Acetyl CoA is an important precursor for various chemicals. We provide a metabolic engineering guideline for the production of acetyl-CoA and other end products from a bacterial chassis. Among 13 pathways that produce acetyl-CoA from glucose, 11 lose carbon in the process, and two do not. The first 11 use the Embden–Meyerhof–Parnas (EMP) pathway to produce redox cofactors and gain or lose ATP. The other two pathways function via phosphoketolase with net consumption of ATP, so they must therefore be combined with one of the 11 glycolytic pathways or auxiliary pathways. Optimization of these pathways can maximize the theoretical acetyl-CoA yield, thereby minimizing the overall cost of subsequent acetyl-CoA-derived molecules. Other strategies for generating hyper-producer strains are also addressed. Acetyl CoA is an important precursor for various chemicals. We provide a metabolic engineering guideline for the production of acetyl-CoA and other end products from a bacterial chassis. Among 13 pathways that produce acetyl-CoA from glucose, 11 lose carbon in the process, and two do not. The first 11 use the Embden–Meyerhof–Parnas (EMP) pathway to produce redox cofactors and gain or lose ATP. The other two pathways function via phosphoketolase with net consumption of ATP, so they must therefore be combined with one of the 11 glycolytic pathways or auxiliary pathways. Optimization of these pathways can maximize the theoretical acetyl-CoA yield, thereby minimizing the overall cost of subsequent acetyl-CoA-derived molecules. Other strategies for generating hyper-producer strains are also addressed. these play a key role in supporting diverse industries as essential basic materials. carboxylic acids that have a straight chain of even-numbered carbon atoms. these use the EMP pathway, H2O2-forming or acetic-acid-forming pyruvate oxidase, combined with phosphotransacetylase or acetate kinase and acetyl-CoA synthetase, respectively, to produce acetyl-CoA from glucose. carboxylic acids with an aliphatic straight carbon chain of 6–12 carbon atoms. carboxylic acids that have a straight chain of odd-numbered carbon atoms. this pathway uses the Embden–Meyerhof–Parnas (EMP) pathway and the pyruvate dehydrogenase complex (PDHc) to split 1 glucose to produce 2 acetyl-CoA with the emission of 2 CO2, producing 4 NADH and 2 ATP. this pathway uses the EMP pathway and pyruvate ferredoxin/flavodoxin oxidoreductase (PFOR) to produce acetyl-CoA from glucose. this uses phosphoketolase (PK) and other enzymes to cycle catalyze fructose-6-phosphate to acetyl phosphate from glucose, which is then converted to acetyl-CoA via phosphotransacetylase. the acetyl phosphate produced can also converted to acetyl-CoA by acetate kinase and acetyl-CoA synthetase. the amount of product generated from 1 l volume of reaction system per hour. the complex is composed of pyruvate dehydrogenase (E1), dihydrolipoamide acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). E1 catalyzes the decarboxylation of pyruvate to CO2 with the formation of C2-hydroxyethylidene thiamin diphosphate (ThDP) intermediate and the reductive acetylation of the lipoyl groups covalently attached to the E2. The E2 transfers an acetyl moiety to CoA to form acetyl-CoA. E3 transfers electrons from the dihydrolipoyl moieties of E2 to FAD and then to NAD. these are used to produce acetyl-CoA coupled with a net production of redox cofactor. when the substrate is totally converted to the product, the yield of the product on that substrate is the theoretical maximum. the PDC-A pathway uses the EMP pathway, PDC, and acetylating acetaldehyde dehydrogenase to produce acetyl-CoA from glucose. PDC-B uses the EMP pathway, PDC, acetaldehyde dehydrogenase, and acetyl-CoA synthetase to produce acetyl-CoA from glucose. PDC-C uses the EMP pathway, PDC, acetate kinase, and phosphotransacetylase to produce acetyl-CoA from glucose. the PFL pathway combines the EMP pathway with pyruvate-formate lyase (PFL) to split one glucose to produce 2 acetyl-CoA with the formation of 2 formate, 2 NADH, and 2 ATP. The PFL-FDH pathway combines the PFL pathway with formate dehydrogenase (FDH) to convert formate acids into CO2, H2O, and redox cofactors. mole or weight conversion rate from feedstock such as glucose to products.