Activation of galactose utilization by the addition of glucose for the fermentation of agar hydrolysate using Lactobacillus brevis ATCC 14869

Objective To investigate the application of carbon catabolite repression (CCR) relaxed Lactobacillus brevis ATCC 14869 in the utilization of agar hydrolysate to produce bioethanol and lactic acid through fermentation. Results As a single carbon source, galactose was not metabolized by L. brevis . However, L. brevis consumed galactose simultaneous to glucose and ceased cell growth after depletion of glucose. For complete use of galactose from agar hydrolysis, glucose need to be periodically replenished into the growth medium. Overall, L. brevis successfully used agar hydrolysate and produced 17.2 g/L of ethanol and 31.9 g/L of lactic acid. The maximum specific cell growth rate on galactose and glucose mixture was the same with the glucose-only medium at 0.12 h −1 . The molar product yields from glucose for lactic acid and ethanol were 1.02 and 0.95 respectively, equal to values obtained from the simultaneous utilization of glucose and galactose. Conclusion In contribution to the ongoing efforts to utilize marine biomass, the relaxed CCR in Lactobacillus brevis ATCC 14869 was herein exploited to produce bioethanol and lactic acid from red seaweed hydrolysates.