Discovery and characterization of a thermostable d-lactate dehydrogenase from Lactobacillus jensenii through genome mining

The demand on thermostable d-lactate dehydrogenases (d-LDH) has been increased for d-lactic acid production but thermostable d-DLHs with industrially applicable activity were not much explored. To identify a thermostable d-LDH, three d-LDHs from different Lactobacillus jensenii strains were screened by genome mining and then expressed in Escherichia coli. One of the three d-LDHs (d-LDH3) exhibited higher optimal reaction temperature (50 °C) than the others. The T5010 value of this thermostable d-LDH3 was 48.3 °C, much higher than the T5010 values of the others (42.7 and 42.9 °C) and that of a commercial d-lactate dehydrogenase (41.2 °C). The Tm values were 48.6, 45.7 and 55.7 °C for the three d-LDHs, respectively. In addition, kinetic parameter (kcat/Km) of d-LDH3 for pyruvate reduction was estimated to be almost 150 times higher than that for lactate oxidation at pH 8.0 and 25 °C, implying that d-lactate production from pyruvate is highly favored. These superior thermal and kinetic features would make the d-LDH3 characterized in this study a good candidate for the microbial production of d-lactate at high temperature from glucose if it is genetically introduced to lactate producing microbial.

► Three kinds of d-lactate dehydrogenase from genome of Lactobacillus jensenii were expressed in E. coli.
► d-LDH3 exhibited higher optimal temperature up to 50 °C compared with those of other d-LDHs.
► The catalytic efficiency (kcat/Km) of d-LDH3 for pyruvate conversion was estimated to be 200 times higher than that for lactate conversion at pH 8.0 and 25 °C.
► The d-LDH3 can be a good candidate biocatalyst for the d-lactate production at high temperature.