A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli.

In this communication we reported the study of a cation channel present in the cytoplasmic membrane of the nitrogen fixing bacterium Rhizobium etli. Inner-membrane (IM) vesicles were purified and fused into planar lipid bilayers (PLBs), under voltage clamp conditions. We have found that fusion of IM-enriched vesicle fractions with these model membranes leads, mainly (>30% of 46 experiments), to the reconstitution of high-conductance channels. Following this strategy, the activity of a channel with main open conductance of 198 pS, in symmetrical 100 mM KCl, was recorded. The single-channel conductance increase to 653 pS in the presence of a 5:1 (cis to trans) gradient of KCl. The channel exhibits voltage dependency and a weak selectivity for cations showing a permeability ratios of P (Rb)/P (K) = 0.96, P (Na)/P (K) = 0.07, and a conductance ratio of gamma(Rb)/gamma(K) = 1.1. The channel here characterized represents a previously undescribed Rhizobium channel although its precise role in rhizobial physiology remains yet to be determined.