Production of high concentration of l-lactic acid from cellobiose by thermophilic Bacillus coagulans WCP10-4

Abstract

Thermophilic Bacillus coagulans WCP10-4 is found to be able to convert cellobiose to optically pure l-lactic acid. Its β-glucosidase activity is detected in whole cells (7.3 U/g dry cells) but not in culture medium, indicating the intracellular location of the enzyme. Its β-glucosidase activity is observed only when cultured using cellobiose as the sole carbon source, indicating that the expression of this enzyme is tightly regulated in cells. The enzyme is most active at 50 °C and pH 7.0. The supplement of external β-glucosidase during fermentation of cellobiose (106 g/l) by B. coagulans WCP10-4 increased the fermentation time from 21 to 23 h and decreased the lactic acid yield from 96.1 to 92.9 % compared to the control without β-glucosidase supplementation. B. coagulans WCP10-4 converted 200 g/l of cellobiose to 196.3 g/l of l-lactic acid at a yield of 97.8 % and a productivity of 7.01 g/l/h. This result shows that B. coagulans WCP10-4 is a highly efficient strain for converting cellobiose to l-lactic acid without the need of supplementing external β-glucosidases.