“…The use of lactic acid in the synthesis of polylactic acid has grown over the years, and high optical purity is an inevitable prerequisite for lactic acid polymerization (1, 23). Strains of Lactobacillus, the largest genus of lactic acid bacteria (LAB), are the most frequently used lactic acid producers (2,4,10,19,22,24), but the optical purities of lactic acid produced by various Lactobacillus strains are markedly different (Table 1) (3,15).The enzymes responsible for L-and D-lactic acid production are NAD-dependent L-lactate dehydrogenases (L-nLDHs) and NAD-dependent D-lactate dehydrogenases (D-nLDHs), respectively, which fall into two different families and are encoded by ldhL and ldhD, respectively (7,20). Lactate racemase, which converts L-lactic acid into D-lactic acid, has only been reported in a few DL-type Lactobacillus strains.…”