Abstract

Salmonella typhimurium can stand against and survive under lethal osmotic exposure. Two systems of osmotic tolerance response(OTR) were found to be utilized by that organism, which were possibly overlapping with each other. The first system is an induction in response to non-lethal high osmoshock(0.3~0.7 M NaCl) at log-phase. The second system is induced during famine condition of stationary-phase. The viability of wild types(UK1, LT2) under these unfavorable conditions was increased by both systems. The viability of stationary-phase cells was approximately 5-fold that of the cells adapted at log-phase. In addition, a few regulatory fenes(rpoS, fur, crp, atp), one carbonstarvation-inducible(cstA104), and an osmotic-inducible gene(proU) were found to play an important role in osmotic tolerance at both growth phases. RpoS, a putative alternative sigma factor (σ^38), was found to participate in OTR systems regardless of growth-phase, but rpoS-defective mutant could still develope the adaptive tolerance. Thus, we concluded that there is rpoS-defective and rpoS-independent systems for osmotic tolerance at both growth-phase. Of the possible otr mutants newly isolated using MudJ(Km, lac) operon fusion techniques, YK3092 (otr201::MudJ) was most sensitive to osmotic challenge regardless of growth phase. It was mapped nearby at 57 min on chromosome and showed rpoS-negative phenotypes such as no catalase activity and inability to accumulate glycogen : but was not linked to rpoS. Therefore, this result strongly suggest that otr201 might be a rpoS-related regulatory gene not gound before.

• Keywords: osmotic tolerance response; S. typhimurium; otr201; rpoS; growth-phase; viability