Abstract
The effects of various amino acids on the growth of lactobacilli (L. gasseri, L. acidophilus, L. fermentum and L. rhamnosus) were investigated. Thirty-eight amino acids (10 mM final concentration) were studied, including both D- and L-forms; glycine was not studied. MRS broth was modified to 40% of the normal concentration and was used as the culture medium. The results showed that phenylalanine and tryptophan promoted growth. However, no concentration dependence was observed for the growth-promoting effects, so improved growth was attributed to an improvement in nutrient balance. Arginine, histidine, cysteine and serine suppressed growth in a concentration-dependent manner, with stronger suppression at higher concentrations. The D-form of cysteine and serine suppressed growth more strongly than the L-form. Growth suppression by arginine and histidine was only observed in L. fermentum, while the suppressing effects of cysteine and/or serine were observed in three strains: L. gasseri, L. acidophilus and L. fermentum. The growth suppression caused by these amino acids is likely due to end product (feedback) inhibition in the biosynthesis of each amino acid. The inhibitory effects of cysteine and serine on the growth of lactobacilli are discussed.
