Abstract

Hydroxyectoine and ectoine were accumulated in the moderately halophilic bacteriumHalomonas ventosae DL7 as dominant compatible solutes in response to the external thermo- and osmo-stresses (30-42°C, 1-3 M NaCl). As the byproduct of ectoine, hydroxyectoine was directly converted from ectoine mediated by the ectoine hydroxylase in DL7, and the hydroxylase gene sequence was obtained by PCR. Further, the activity of ectoine hydroxylase of strain DL7 cells in vitro was determined at 30 to 42°C, and the thermo-stress conduce the inhibition of this enzyme activity. In addition, DL7 cells showed similar growth level when grown in presence of same level ectoine or hydroxyectoine (1 mM) in medium with high salinity (2-2.7 M NaCl). However, the presence of hydroxyectoine showed higher growth level than ectoine when DL7 cells were incubated at 42°C. The results showed that the alteration of temperature instead of salinity stress obviously stimulated the expression of ectoine hydroxylase, but inhibited its activity, and hydroxyectoine with ectoine together played an important role as thermo- and osmo-protectants in strain DL7 to cope with high temperature and salinity environment.

Key words: Halomonas ventosae DL7, compatible solutes, hydroxyectoine, ectoine hydroxylase, thermo-stress, osmo-stress.