Emerging Electrophysiology of Facultative Bacterial Pathogens

Abstract

In contrast to strictly marine microorganisms or obligatory parasites dwelling in a constant environment, facultative pathogens that spend part of their life inside the host and part as free-living forms possess exquisitely robust osmoregulation. Their survival and persistence in highly variable conditions outside of the host defines the pathways and efficacy of transmission. Giant spheroplasts as a system for patch-clamp recording, previously developed for E. coli, already permitted detailed characterization of osmoprotective tension-activated channels in this organism, but homologous channels from other bacteria have never been recorded in their native setting. We have recently developed giant spheroplast preparations for Vibrio cholerae and Pseudomonas aeruginosa. The first patch-clamp survey of both organisms revealed channels with conductances and gating phenotypes similar to MscS and MscL of E. coli, with comparable tension midpoints. Conductive responses to saturating tension are dominated by MscL-like channels in both species. Analysis of genomes pointed to single orthologs of MscL and MscS in V. cholereae, but P. aeruginosa, in addition to MscL, possesses two mscS-like channel genes. Homology models reveal differences from E. coli channels in the distributions of charged and aromatic residues, underlying potentially different interactions with lipids. MS channels in both species are modulated by ampthipathic autoinducers (CAI-1 and PAI-1) from respective bacterial species, which shift their activation curves to the right on the tension scale. This apparently indirect effect mediated by a distorted lateral pressure profile in the membrane suggests that autoinducers easily partition into the cytoplasmic membranes of these bacteria and may not require special transport systems for entry. Amenability to patch-clamp recording for the two new bacterial species opens broad opportunities for studies of solute permeability and electrogenic transport in their membranes.