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Physiological Roles of Three Na + /H + Antiporters in the Halophilic Bacterium Vibrio parahaemolyticus
Author(s) -
Kuroda Teruo,
Mizushima Tohru,
Tsuchiya Tomofusa
Publication year - 2005
Publication title -
microbiology and immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.664
H-Index - 70
eISSN - 1348-0421
pISSN - 0385-5600
DOI - 10.1111/j.1348-0421.2005.tb03662.x
Subject(s) - antiporters , vibrio parahaemolyticus , antiporter , halophile , mutant , biology , strain (injury) , bacteria , microbiology and biotechnology , homeostasis , biochemistry , membrane , anatomy , genetics , gene
Vibrio parahaemolyticus mutants lacking three Na + /H + antiporters (NhaA, NhaB, NhaD) were constructed. The AnhaA strains showed significantly higher sensitivity to LiCl regarding their growth compared to the parental strain. The AnhaA and AnhaB strains exhibited higher sensitivities to LiCl. The mutant XACabd lacking all of the three antiporters could not grow in the presence of 500 mM LiCl at pH 7.0, or 50 mM at pH 8.5. The XACabd mutant was also sensitive to 1.0 M NaCl at pH 8.5. These results suggest that Na + /H + antiporters, especially NhaA, are responsible for resistance to LiCl and to high concentrations of NaCl. Reduced Na + /H + and Li + /H + antiport activities were observed with everted membrane vesicles of AnhaB strains. However, Li + /H + antiport activities of AnhaB strains were two times higher than those of AnhaA strains when cells were cultured at pH 8.5. It seems that expression of nhaA and nhaB is dependent on medium pH to some extent. In addition, HQNO (2‐heptyl‐4‐hydroxyquinoline N ‐oxide), which is a potent inhibitor of the respiratory Na + pump, inhibited growth of XACabd, but not of the wild type strain. Moreover, survival rate of XACabd under hypoosmotic stress was lower than that of wild type strain. It is likely that the Na + /H + antiporters are involved in osmoregulation under hypoosmotic stress. Based on these findings, we propose that the Na + /H + antiporters cooperate with the respiratory Na + pump in ionic homeostasis in V. parahaemolyticus