Cloning, functional expression and primary characterization of Vibrio parahaemolyticus K+/H+ antiporter genes in Escherichia coli

Abstract

The regulation of internal Na+ and K+ concentrations is important for bacterial cells, which, in the absence of Na+ extrusion systems, cannot grow in the presence of high external Na+. Likewise, bacteria require K+ uptake systems when the external K + concentration becomes too low to support growth. At present, we have little knowledge of K+ toxicity and bacterial outward-directed K+ transport systems. We report here that high external concentrations of K+ at alkaline pH are toxic and that bacteria require K+ efflux and/or extrusion systems to avoid excessive K + accumulation. We have identified the first example of a bacterial K+(specific)/H+ antiporter, Vp-NhaP2, from Vibrio parahaemolyticus. This protein, a member of the cation: proton antiporter-1 (CPA1) family, was able to mediate K+ extrusion from the cell to provide tolerance to high concentrations of external KCl at alkaline pH. We also report the discovery of two V. parahaemolyticus Na+/H+ antiporters, Vp-NhaA and Vp-NhaB, which also exhibit a novel ion specificity toward K+, implying that they work as Na+(K +)/H+ exchangers. Furthermore, under specific conditions, Escherichia coli was able to mediate K+ extrusion against a K + chemical gradient, indicating that E. coli also possesses an unidentified K+ extrusion system(s). © 2005 Blackwell Publishing Ltd.