Homolactic Acid Fermentation by the Genetically Engineered Thermophilic Homoacetogen Moorella thermoacetica ATCC 39073.

For the efficient production of target metabolites from carbohydrates, syngas, or H-CO by genetically engineered , the control of acetate production (a main metabolite of ) is desired. Although propanediol utilization protein (PduL) was predicted to be a phosphotransacetylase (PTA) involved in acetate production in , this has not been confirmed. Our findings described herein directly demonstrate that two putative PduL proteins, encoded by Moth_0864 () and Moth_1181 (), are involved in acetate formation as PTAs. To disrupt these genes, we replaced each gene with a lactate dehydrogenase gene from ATCC 33223 (). The acetate production from fructose as the sole carbon source by the deletion mutant was not deficient, whereas the disruption of significantly decreased the acetate yield to approximately one-third that of the wild-type strain. The double-deletion (both genes) mutant did not produce acetate but produced only lactate as the end product from fructose. These results suggest that both genes are associated with acetate formation via acetyl-coenzyme A (acetyl-CoA) and that their disruption enables a shift in the homoacetic pathway to the genetically synthesized homolactic pathway via pyruvate. This is the first report, to our knowledge, on the experimental identification of PTA genes in and the shift of the native homoacetic pathway to the genetically synthesized homolactic pathway by their disruption on a sugar platform.