The mechanoelectrical response of the cytoplasmic membrane of Vibrio cholerae

Abstract

Persistence of Vibrio cholerae in waters of fluctuating salinity relies on the capacity of this facultative enteric pathogen to adapt to varying osmotic conditions. In an event of osmotic downshift, osmolytes accumulated inside the bacterium can be quickly released through tension-activated channels. With the newly established procedure of giant spheroplast preparation from V. cholerae, we performed the first patch-clamp characterization of its cytoplasmic membrane and compared tension-activated currents with those in Esherichia coli. Saturating pressure ramps revealed two waves of activation belonging to the ~1-nS mechanosensitive channel of small conductance (MscS)- like channels and ~3-nS mechanosensitive channel of large conductance (MscL)-like channels, with a pressure midpoint ratio p0.5MscS/p0.5MscL of 0.48. We found that MscL-like channels in V. cholerae present at a density three times higher than in E. coli, and yet, these vibrios were less tolerant to large osmotic downshocks. The Vibrio MscSlike channels exhibit characteristic inward rectification and subconductive states at depolarizing voltages; they also adapt and inactivate at subsaturating tensions and recover within 2 s upon tension release, just like E. coli MscS. Trehalose, a compatible internal osmolyte accumulated under hypertonic conditions, significantly shifts activation curves of both MscL- and MscS-like channels toward higher tensions, yet does not freely partition into the channel pore. Direct electrophysiology of V. cholerae offers new avenues for the in situ analysis of membrane components critical for osmotic survival and electrogenic transport in this pathogen. © 2013 Rowe et al.