title: 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).
authors.affiliation: Department of Microbiology, Niigata University of Pharmacy and Applied Life Sciences, Niigata 950-2081, Japan.
authors.forename: Martha V
authors.initials: MV
authors.lastname: Radchenko
authors.forename: Rungaroon
authors.initials: R
authors.lastname: Waditee
authors.forename: Sawako
authors.initials: S
authors.lastname: Oshimi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Fukuhara
authors.forename: Teruhiro
authors.initials: T
authors.lastname: Takabe
authors.forename: Tatsunosuke
authors.initials: T
authors.lastname: Nakamura
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics*; D004983:Ethanolamines / Q000494:pharmacology; D017136:Ion Transport; D011188:Potassium / Q000378:metabolism; D027961:Potassium-Hydrogen Antiporters / Q000235:genetics*; D014736:Vibrio parahaemolyticus / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004983:Ethanolamines; D027961:Potassium-Hydrogen Antiporters; C020283:diethanolamine; D011188:Potassium