The effect of sodium acetate on the activity of L- and D-lactate dehydrogenases in Lactobacillus sakei NRIC 1071(T) and other lactic acid bacteria

The effect of sodium acetate on the production of stereoisomers of lactic acid produced by Lactobacillus sakei NRIC 1071(T) and other lactic acid bacteria was studied. L. sakei NRIC 1071(T) started producing L-lactic acid at the early logarithmic phase and d-lactic acid at the late logarithmic phase. The activity of L-lactate dehydrogenase [EC 1.1.1.27, L-LDH] from the resting cells of L. sakei NRIC 1071(T) appeared at the early stage of the logarithmic phase during the growth, and the activity of D-lactate dehydrogenase [EC 1.1.1.28, D-LDH] at the late stage of the logarithmic phase. The resting cells and cell-free extracts of L. sakei NRIC 1071(T) did not produce DL-lactic acid from L- or D-lactic acid. Stained bands of L-LDH and D-LDH appeared in the cell-free extracts from the cells of L. sakei NRIC 1071(T). Consequently, L. sakei conclusively produced L- and D-lactic acid by the action of L-LDH and D-LDH. This finding leads to the conclusion that lactate racemase [EC 5.1.2.1] does not exist in this strain. When the specific activity of LDHs (the total activity of L-LDH plus D-LDH) from the cells cultivated in the presence of sodium acetate is compared with that cultivated in its absence, the ratio of the activity between the cells cultivated in the former condition and those in the latter fell from 1.7 on the cell-free extracts to 1.3 on the preparation of the QAE-Toyopearl 550c chromatography. This result indicates that the amount of LDHs in the cells of L. sake NRIC 1071(T) cultivated in the presence of 50 mM sodium acetate was much more than that in the cells cultivated in the absence of sodium acetate. The shift of the type of stereoisomers of lactic acid from the DL-type to the L-type is discussed in the case of L. sakei strains.