Physiological diversity and adaptations of aerobic heterotrophic bacteria from different depths of hypersaline, heliothermal and meromictic Ekho Lake (East Antarctica)

The hypersaline and meromictic Ekho Lake provides, with increasing depth, a large variety of different habitats to microorganisms. Out of 250 isolates, 51 bacterial strains were studied for physiological adaptations to their environment (i.e. to the depth layer from which they were obtained). Their salinity and temperature tolerance ranges for growth reflected the very conditions that were measured in the samples of their origin collected in the summer of 1989/1990. These observations indicated that the isolates are capable of growth at the depth of their origin and that they conceivably were endemics. Additionally, a separation of physiologically different populations of heterotrophic bacteria was indicated with respect to the utilization of C-compounds: the uppermost 4 m of the oxylimnion (with frequent water turnover and more extreme temperature conditions) supported primarily sugar-utilizing and halotolerant x-Proteobacteria and Gram-positives. The deeper, hypersaline and heliothermally heated layers ( > 4-24 m) had more moderately halophilic and amino acid-utilizing gamma -Proteobacteria possibly of marine origin.