Abstract: Salmonella typhimurium adapts to environmental stresses through its own regulatory system, in which the stationary-phase?sigma?(RpoS) factor plays an important role. The objective of this study was to construct a rpoS-defective mutant strain (SL1344/DrpoS) of S. typhimurium SL1344 using Red homologous recombination technique and to compare the growth of SL1344/DrpoS and SL1344 under different stresses including 3.5% NaCl, 42 ℃, and pH 4.0. Besides, this research also focused on the effect of pre-treatment of Salmonella with different concentrations of salt on its growth in a medium containing 3.5% NaCl in order to demonstrate the effect of rpoS on the adaptability of S. typhimurium to the stressful environment. The results showed that the growth of both strains was inhibited by 3.5% NaCl, and SL1344/DrpoS was more significantly inhibited. The maximum growth rate of SL1344 was 2.49 times as higher as that of SL1344/DrpoS. Under the conditions of 42 ℃ and pH 4.0, the maximum growth rate of SL1344 was 1.33 and 2.77 times as higher as that of SL1344/DrpoS, respectively. There were differences in the growth of the two strains after stimulation by different salt concentrations for different times. The construction of SL1344/DrpoS can lay the foundation for further study on the role of RpoS of S. typhimurium in response to environmental stresses and for the prevention and treatment of salmonellosis.

Key words: Salmonella typhimurium, gene knockout, RpoS, osmotic pressure, temperature, pH