SmcR, the Quorum-sensing Master Regulator, Is Partially Involved in Temperature/Salinity-mediated Changes in MetalloproteasevvpEExpression inVibrio vulnificus

Vibrio vulnificus, a gram-negative halophilic marine bacterium and opportunistic human pathogen, must withstand various environmental changes, especially simultaneous changes in temperature and salinity, from 25℃/2.5% to 37℃/0.9% (SCTS) upon entering the human body. In our previous study, SCTS stimulated vvpE expression even in the background of a mutation in luxS encoding LuxS enzyme for the biosynthesis of quorum-sensing (QS) signal molecule autoinducer-2 (AI-2), suggesting that the A1-2-mediated QS system is partially involved in the SCTS-mediated change of vvpE expression. In this study, we examined the effects of the QS master regulator SmcR on SCTS-mediated changes in vvpE expression and extracellular VvpE production. SCTS stimulated V. vulnificus growth, but with no increase in maximal growth levels. The SCTS-mediated prolongation of the stationary growth phase resulted in a significant increase in growth phase-dependent smcR and vvpE expressions. A mutation in smcR seriously repressed vvpE expression, but had no significant effect on V. vulnificus growth. However, the smcR mutation only partially attenuates SCTS-mediated changes in vvpE expression. These results indicate that SCTS stimulates the expressions of smcR and vvpE by stimulating V. vulnificus growth, and that SmcR is only partially involved in SCTS-mediated changes in vvpE expression.