Isolation of adh mutant of Lactobacillus rhamnosus for production of L(+) Lactic acid

Abstract

Lactobacillus rhamnosus, a facultative anaerobe, which produces L (+) lactic acid and ethanol under anaerobic conditions, is used in the present study. An adh^- mutant of Lactobacillus rhamnosus MTCC 1408, was developed by chemical mutagenesis, which could produce pure L(+) lactic acid as the only product. Batch fermentation kinetics of the wild type and the mutant strain were studied in glucose-yeast extract medium under conditions of temperature 40ºC and pH 6.2 anaerobically. The biomass yield was similar in both wild type and mutant strains, however lactic acid yield increased by 6.6%. A chemically defined media was optimized for supplementation of succinate, acetate and citrate for better biomass formation using single variable optimisation. It was further optimised for varying concentrations of vitamins, amino acids and trace metals by response surface method. The batch biomass yield (0.1g/g) and lactic acid yield (0.88g/g) in the optimised chemically defined media were similar to those obtained in the glucose-yeast extract medium.