Ectoines as compatible solutes and carbon and energy sources for the halophilic bacterium Chromohalobacter salexigens
Abstract
Aims: To investigate the catabolism of ectoine and hydroxyectoine, which are the major compatible solutes synthesized by Chromohalobacter salexigens. Methods and Results: Growth curves performed in M63 minimal medium with low (0·75 mol l-1 NaCl), optimal (1·5 mol l-1 NaCl) or high (2·5 mol l-1 NaCl) salinity revealed that betaine and ectoines were used as substrate for growth at optimal and high salt. Ectoine transport was maximal at optimal salinity, and showed 3- and 1·5-fold lower values at low and high salinity respectively. The salt-sensitive ectA mutant CHR62 showed an ectoine transport rate 6·8-fold higher than that of the wild type. Incubation of C. salexigens in a mixture of glucose and ectoine resulted in a biphasic growth pattern. However, CO2 production due to ectoine catabolism was lower, but not completely abolished, in the presence of glucose. When used as the sole carbon source, glycine betaine effectively inhibited ectoine and hydroxyectoine synthesis at any salinity. Conclusions: The catabolic pathways for ectoine and hydroxyectoine in C. salexigens operate at optimal and high (although less efficiently) salinity. Endogenous ectoine(s) may repress its own transport. Ectoine utilization was only partially repressed by glucose. Betaine, when used as carbon source, suppresses synthesis of ectoines even under high osmolarity conditions. Significance and Impact of the Study: This study is a previous step to the subsequent isolation and manipulation of the catabolic genes, so as to generate strains with enhanced production of ectoine and hydroxyectoine