Molecular identification and physiological characterization of halophilic and alkaliphilic bacteria belonging to the genus Halomonas

Alkaline saline lakes are unusual extreme environments formed in closed drainage basins. Qabar - oun and Um - Alma lakes are alkaline saline lakes in the Libyan Sahara. There were only a few reports (Ajali et al., 1984) on their microbial diversity before the current work was undertaken. Five Gram-negative bacterial strains, belonging to the family of Halomonadaceae, were isolated from the lakes by subjecting the isolates to high salinity medium, and identified using 16S rRNA gene sequencing as Halomonas pacifica, Halomonas sp, Halomonas salifodinae, Halomonas elongata and Halomonas campisalis. Two of the Halomonas species isolated (H. pacifica and H. campisalis) were chosen for further study on the basis of novelty (H. pacifica) and on dual stress tolerance (high pH and high salinity) shown by H. campisalis. Both species showed optimum growth at 0.5 M NaCl, but H. campisalis alone was able to grow in the absence of NaCl. H. pacifica grew better than H. campisalis at high salinities in excess of 1 M NaCl and was clearly a moderately halophile. H. pacifica showed optimum growth at pH 7 to 8, but in contrast H. campisalis could grow well at pH values up to 10. 13C - NMR spectroscopy was used to determine and identify the compatible solutes accumulated by H. pacifica and H. campisalis grown in rich and minimal media at different concentrations of NaCl. H. pacifica and H. campisalis accumulated betaine in rich (LB) medium with ectoine only appearing at the highest salinity tested (2.5 M NaCl). In contrast, in M9 minimal medium, no betaine was detected and ectoine and hydroxyectoine were accumulated at high salinities. H. campisalis was able to grow well with urea or nitrate as the sole source of nitrogen and was shown to be capable of efficiently removing nitrate from the medium under aerobic assimilatory conditions, where it is incorporated into biomass.