title: The pha2 gene cluster involved in Na+ resistance and adaption to alkaline pH in Sinorhizobium fredii RT19 encodes a monovalent cation/proton antiporter.
abstract: Sinorhizobium fredii RT19 can tolerate up to 0.6 M NaCl, whereas all its pha2-disrupted mutants, constructed by Tn5 mutagenesis, failed to grow in even the presence of 0.1 M NaCl. No growth difference was detected in pha2 mutants at a pH<7.5 in the presence or absence of K+, but growth reduction was observed in the presence of K+ when pH>7.5. The pha2 gene cluster was able to completely restore the growth of the pha2 mutants of S. fredii RT19 in 0.6 M NaCl. Measurement of monovalent cation intracellular content suggested that pha2 was involved in both Na+ (Li+) and K+ efflux. The pha2 mutants exhibited K+/H+, but no apparent Na+(Li+)/H+ antiporter activity in everted membrane vesicles. Taken together, these results indicated that the pha2 cluster of S. fredii RT19 encodes a monovalent cation/proton antiporter involved in resistance to Na+ and adaption to pH, which was very different from the pha1 cluster of Sinorhizobium meliloti, which encodes a K+/H+ antiporter.
authors.affiliation: Department of Microbiology and Immunology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, Beijing, China.
authors.forename: Lifu
authors.initials: L
authors.lastname: Yang
authors.forename: Juquan
authors.initials: J
authors.lastname: Jiang
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Susheng
authors.initials: S
authors.lastname: Yang
mesh_terms: D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000378:metabolism; D009154:Mutation; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D027961:Potassium-Hydrogen Antiporters / Q000378:metabolism; D042181:Sinorhizobium fredii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: D027682:Cation Transport Proteins; D027961:Potassium-Hydrogen Antiporters; D008094:Lithium; D012964:Sodium; D011188:Potassium