Salt-tolerance genes involved in cation efflux and osmoregulation of Sinorhizobium fredii RT19 detected by isolation and characterization of Tn5 mutants

Authors

  • Ju Quan Jiang,

    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author
  • Wei Wei,

    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author
  • Bing Hai Du,

    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author
  • Xiao Hong Li,

    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author
  • Lei Wang,

    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author
  • Su Sheng Yang

    Corresponding author
    1. Department of Microbiology, College of Biological Sciences, China Agricultural University and Key Laboratory of Agro-Microbial Resource and Application, Ministry of Agriculture, No. 2 Yuanmingyuan West Road, Beijing, 100094, PR China
    Search for more papers by this author

  • Edited by A. Oren

*Corresponding author. Tel.: +86 10 62732674; fax: +86 10 62731332, E-mail address: yangssh@cau.edu.cn

Abstract

Salt-tolerance genes of Sinorhizobium fredii RT19 were identified by the construction and screening of a transposon Tn5-1063 library containing over 30,000 clones. Twenty-one salt-sensitive mutants were obtained and five different genes were identified by sequencing. Eight mutants were found with disruptions in the phaA2 gene, which encodes a cation efflux system protein, while mutations in genes encoding other cation effux system proteins were found in seven (phaD2), two (phaF2) and two (phaG2) mutants. A mutation in the metH gene, encoding 5′ methyltetrahydrofolate homocysteine methyltransferase, was found in two of the salt sensitive strains. Growth experiments showed that phaA2, phaD2, phaF2 and phaG2 mutants were hypersensitive to Na+/Li+ and slightly sensitive to K+ and not sensitive to sucrose and that metH mutants were highly sensitive to any of Na+, Li+, K+ and sucrose. Na+ intracellular content measurements established that phaA2, phaD2, phaF2 and phaG2 are mainly involved in the Na+ efflux in S. fredii RT19. Recovery of growth of the metH mutants incubated with different concentrations of NaCl could be obtained by additions of methionine, choline and betaine, which showed that the metH gene is probably involved in osmoregulation in S. fredii RT19.

Ancillary