Protection of Escherichia coli cells against extreme turgor by activation of MscS and MscL mechanosensitive channels: identification of genes required for MscS activity

Mechanosensitive channels are ubiquitous amongst bacterial cells and have b een proposed to have major roles in the adaptation to osmotic stress, in pa rticular in the management of transitions from high to low osmolarity envir onments. Electrophysiological measurements have identified multiple channel s in Escherichia coli cells, One gene, mscL, encoding a large conductance c hannel has previously been described, but null mutants were without well-de fined phenotypes, Here, we report the characterization of a new gene family required for MscS function, YggB and KefA, which has enabled a rigorous te st of the role of the channels. The channel determined by KefA does not app ear to have a major role in managing the transition from high to low osmola rity, In contrast, analysis of mutants of E,coli lacking YggB and MscL show s that mechanosensitive channels are designed to open at a pressure change just below that which would cause cell disruption leading to death.