Abstract
Fluctuation test was performed to determine the frequency and nature of mutations in strains Salmonella typhimurium SF553 and JF2794 having different rpoS genotypes. The role of rpoS gene in adaptive mutagenesis was revealed. The frequency of His(+) reversions as well as mutations in kanamycin and rifampicin resistance genes was 2-8 times higher in S. typhimurium SF553 (rpoS(+)) than in S. typhimurium JF2794 (rpoS(-)). S. typhimurium SF553 was more resistant to death under starvation conditions than S. typhimurium JF2794; however, the difference in viability of the cultures was less than 30%. Our results suggest that variations in the mutation frequency of these two strains can be explained by the fact that rpoS is directly involved in adaptive mutagenesis. We hypothesize that RpoS protein plays a regulatory role in the activation of stress-induced mutagenesis in bacteria.