Inhibition of Induced Mutagenesis in Salmonella typhimurium by the Protein of Propionibacterium freudenreichii subsp. shermanii

Culture liquid and cells of Propionibacterium freudenreichii subsp. shermanii VKM-103 exerted a strong antimutagenic effect on mutations induced by 4-nitroquinoline-1-oxide, N-methyl-N′-nitro-N′-nitrosoguanidine, sodium azide (base pair substitutions) and 9-aminoacridine (frameshift mutations). No inhibitory effect was observed against mutagenesis induced by 2-nitrofluorene (frameshift mutations). The highest antimutagenic activity was found in the culture liquid of cells grown for 24 h. Acetic and propionic acids of the culture liquid produced by propionibacteria made no observable contribution to the antimutagenicity. Antimutagenic activity of the culture liquid was considerably reduced by protease treatment and by heating at 92°C for 10 min. Upon dialysis, the culture liquid lost almost all of its inhibitory activity. Cell wash solution also contained high antimutagenic activity which was lost upon protease treatment and dialysis. According to the exclusion limit of the dialysis bag, the molecular weight of the antimutagenic factor, presumably a protein, is less than 1.5 kDa. In addition, the cells of P. shermanii were capable of binding or modifying the mutagens, thereby decreasing their mutagenicity.