The pha2 gene cluster involved in Na+ resistance and adaption to alkaline pH in Sinorhizobium fredii RT19 encodes a monovalent cation/proton antiporter.

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.
FEMS Microbiology Letters (Impact Factor: 2.05). 09/2006; 262(2):172-7. DOI: 10.1111/j.1574-6968.2006.00385.x
Source: PubMed

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.

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