title: Metagenomic cloning and characterization of Na⁺ transporters from Huamachi Salt Lake in China.
abstract: Moderately halophilic bacteria are a kind of extreme environment microorganism that can tolerate moderate salt concentrations ranging from 0.5M to 2.5M. Here, via a metagenomic library screen, we identified four putative Na(+) transporters, designated H7-Nha, H16-Mppe, H19-Cap and H35-Mrp, from moderately halophilic community in the hypersaline soil of Huamachi Salt Lake, China. Functional complementation observed in a Na(+)(Ca(2+))/H(+) antiporter-defective Escherichia coli mutant (KNabc) suggests that the four putative Na(+) transporters could confer cells a capacity of Na(+) resistance probably by enhancing Na(+) or Ca(2+) efflux, but not Li(+) or K(+) exchange. Blastp analysis of the deduced amino-acid sequences indicates that H7-Nha has 71% identity to the NhaG Na(+)/H(+) antiporter of Bacillus subtilis, while H19-Cap shows 99% identity to Enterobacter cloacae Ca(2+) antiporter. Interestingly, H16-Mppe shares 59% identity to the metallophosphoesterase of Bacillus cellulosilyticus and H35-Mrp shows 68% identity to multidrug resistance protein of Lysinibacillus sphaericus. This is the first report that predicts a potential role of metallophosphoesterase in Na(+) resistance in halophilic bacteria. Furthermore, everted membrane vesicles prepared from E. coli cells harboring H7-Nha exhibit Na(+)/H(+) antiporter activity, but not Li(+) (K(+))/H(+) antiporter activity, confirming that H7-Nha supports Na(+) resistance mainly via Na(+)/H(+) antiport. Our report also demonstrates that metagenomic library screen is a convenient and effective way to explore more novel types of Na(+) transporters.
authors.affiliation: State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing 100193, People's Republic of China.
authors.forename: Miao
authors.initials: M
authors.lastname: Gao
authors.forename: Li
authors.initials: L
authors.lastname: Tao
authors.forename: Sanfeng
authors.initials: S
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002681:China; D003001:Cloning, Molecular / Q000379:methods*; D004950:Esterases / Q000235:genetics / Q000378:metabolism; D060106:Lakes / Q000737:chemistry / Q000382:microbiology*; D054892:Metagenome; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride / Q000378:metabolism* / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D004950:Esterases