(436e) D-Lactic Acid Fermentation and Enzymatic Activities of a Novel Bacterium Terrilactibacillus Laevilacticus SK5-6

In this study, Terrilactibacillus laevilacticus SK5-6, a novel D-lactate producer, was proven to exhibit a good fermentation performance comparable to the reference D-lactate producer Sporolactobacillus sp. A catalase positive T. laevilacticusSK5-6 produced D-lactate at higher yield, productivity, and optical purity compared with Sporolactobacillus laevolacticus0361^T. Investigation on the glucose metabolism for D-lactate along with the activation of the key enzymes was conducted. The results suggested that D-lactate production and its optical purity were controlled by the key enzymes in glycolysis pathway by their allosteric mechanisms. The results suggested that rapid bioconversion of glucose to D-lactate by T. laevilacticus SK5-6 was responsible by the expression of these key enzymes during the fermentation stage. Among 5 key enzymes observed, phosphofructokinase (PFK) possessed the lowest specific activity; thus, the conversion of fructose-6-phosphate to fructose-1,6-phosphate (F-1,6-P) was considered the rate limiting step. Pyruvate kinase (PYK) was proven to involve in ATP regeneration; therefore, playing role in driving the glycolysis flux. Lactate dehydrogenase (LDH) was allosterically activated by F-1,6-P. With the highest specific activity of LDH followed by PYK and PFK, respectively, this simultaneously drove glucose flux toward lactate at a high rate. Compensation of yeast extract in the preculture medium by ammonium salts, e.g., NH₄Cl and (NH₄)₂HPO₄ was conducted. Complete glucose consumption was observed in the fermentation using NH₄Cl supplemented in preculture medium which yielded a high lactate titer of 102.5 g/L within 48 h with the production yield of 0.84 g/g and the optical purity of 99.74 % enantiomer excess.