Isolation and characterization of salt-sensitive mutants of the moderately halophilic bacterium Salinivibrio costicola subsp. yaniae.

Salinivibrio costicola subsp. yaniae is a moderately halophilic bacterium which can grow over a wide range of salinity. In response to external osmotic stress (1-3 M NaCl), S. costicola subsp. yaniae can accumulate ectoine, glycine betaine, and glutamate as compatible solutes. We used suicide plasmids pSUP101 to introduce transposon Tn1732 into S. costicola subsp. yaniae via Escherichia coli SM10 mediated by conjugation. One Tn1732-induced mutant, MU1, which was very sensitive to the external salt concentration, was isolated. Mutant MU1 did not grow above 1.5 M NaCl and did not synthesize ectoine, but accumulated Ngamma-acetyldiaminobutyrate, an ectoine precursor, as confirmed by (1)H-NMR analysis. From these data, we concluded that ectoine performs a key role in osmotic adaptation towards high salinity environments in strain S. costicola subsp. yaniae.