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.

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 Gassericin T is a two-component lactacin F-family bacteriocin, and its productive genes have been reported to widely spread over other Lactobacillus gasseri strains. Lb. gasseri LA158 isolated from feces of a human infant had been also presumed to produce gassericin T. In this study, we determined the full-length sequence of gassericin T operon and confirmed production of gassericin T on Lb. gasseri LA158. Nucleotide sequencing revealed 6.3-kb region containing nine genes, gatPKRTCZAXI, responsible for gassericin T production, immunity, secretion and regulation. The latter five genes were identical to gat genes of another strains already reported. In addition, the nine genes had highly homology to some genes of the other lactacin F-family bacteriocins. Purification of gassericin T from the culture supernatant of Lb. gasseri LA158 cultivated in a cheese whey-based medium was addressed using dialysis and hydrophobic and reverse-phase chromatography. In the final step using RP-HPLC, a broad peak fraction with antibacterial activity was collected. MS analysis showed coexistence of the two component peptides (mature GatA and GatX) of gassericin T in the fraction. These results present certain genetic and biochemical evidence for gassericin T production from Lb. gasseri LA158. Production of gassericin T in the food-grade cheese whey-based medium would contribute to the future use of gassericin T and its producers for food biopreservation.

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