Intestinal bacteria, including the facultative pathogen Vibrio cholerae , can adapt to a wide range of osmotic environments. In high-osmolarity media, bacteria accumulate small compatible metabolites to maintain turgor pressure, but under drastic osmotic down-shifts bacteria are able to avoid mechanical rupture by rapidly releasing these metabolites through mechanosensitive (MS) channels. Previous experiments on V. cholerae have identified two major types of MS channels - MscS and MscL. We functionally examine these channels' specific roles in Vibrio's osmotic rescuing via genetic modification, bacterial patch-clamp electrophysiology, and stopped-flow light scattering. The light scattering kinetics revealed that WT Vibrio cells were capable of releasing up to 10% of their total non-aqueous content within ∼30 ms. To investigate each channel's individual contribution to V. cholerae's osmotic permeability response, we generated and characterized the first individual ΔmscS, ΔmscL , and double ΔmscL ΔmscS mutants in V. cholerae O395. Both mutants lacking MscS exhibited delayed osmolyte release kinetics and decreased osmotic survival rates compared to WT. Surprisingly, the ΔmscL mutant had comparable kinetics to WT, but a much higher osmotic survival, whereas Δ mscS had low survival, comparable to the double ΔmscL Δ mscS mutant. The data indicate that MscS is much more efficient in osmotic adjustment and is up-regulated in the absence of MscL, whereas in the absence of the low-threshold MscS, MscL even becomes toxic. Kinetic modeling of the cell swelling process and channel activation reveals the advantage of low-threshold MscS in curbing tension surges in Vibrio and its role in proper termination of the osmotic permeability response.

MscS is a critical component for osmotic survival ofVibrio cholerae