Strain improvement of Lactobacillus delbrueckii NCIM 2365 for lactic acid production

Abstract

Various nitrogen sources were compared with yeast extract for efficient lactic acid production by Lactobacillus delbrueckii (NCIM 2365). None of the nitrogen source gave lactic acid concentration as high as that for yeast extract. The effect of yeast extract could have been due to its B vitamin content. Acclimatization and ultraviolet mutagenesis were used to develop strains of L. delbrueckii (NCIM 2365) that produced increased lactic acid concentrations. Four mutants (Ac-1, Ac-2, Uc-1 and Uc-3) were compared with the wild type L. delbrueckii with 100 g/l cane sugar concentration in a fermentation medium. All the four mutants produced higher levels of lactic acid with enhanced productivity than the wild type. Lactic acid fermentation from various carbohydrates by both wild strain and mutant Uc-3 was investigated. Sucrose, xylose and maltose were not utilized by both the wild and mutant strains. When the cultures were grown in a fermentation medium containing glucose, fructose, lactose or galactose as a carbon source, the average volumetric productivities exhibited by mutant Uc-3 were higher than those of wild strain. Mutant Uc-3 was compared with wild type, L. delbrueckii NCIM 2365 by fermentation with different concentrations of hydrolyzed cane sugar. The highest lactic acid concentration (135 g/l) in batch fermentation was obtained with 150 g/l of cane sugar with 90% lactic acid yield. Overall, mutants exhibited faster growth rates, shorter lag phases, higher productivity and greater lactic acid yield.