Cloning and Heterologous Expression of Lactate Dehydrogenase Genes from Acid-Tolerant Lactobacillus acetotolerans HT.

Lactic acid (LA) has been used for wide range of food processing and industrial applications, for example, as a raw material of biodegradable plastics, poly(lactic acid)s (PLAs). Thus, there is a demand to incorporate acid-resistance for effective LA production. Acid-tolerant lactic acid bacteria (LAB), Lactobacillus acetotolerans HT, has been isolated from rice vinegar (pH 2.9, 6 % acetic acid). In this study, genes for the D- and L-lactate dehydrogenases (D-LDH, L-LDH1, and L-LDH2) of Lb. acetotolerans HT, which constitute the key enzymes in cell growth and lactic acid production, were cloned and identified. Through heterologous expression of LDH genes in Escherichia coli DH5a, recombinant E. coli DH5a harboring the D-LDH (IdhD) or L-LDH1 (IdhLl) genes were found to produce D-LA or L-LA, respectively, whereas the strain harboring the L-LDH2 (ldhL2) gene did not produce L-LA. This finding strongly suggests that the translational product of the ldhL2 gene does not exhibit L-LDH activity in vivo. [ABSTRACT FROM AUTHOR]