Growth characteristics, effects of temperature, and ion specificity of the halotolerant bacterium Halomonas elongata

The genus Halomonas (type species H. elongata) is a new bacterial genus composed of salt tolerant bacteria. The growth characteristics and morphology of the type strain of this bacterial group were studied using both complex and defined media. The salt tolerance of the bacterium decreased significantly on defined medium, suggesting that the type of growth medium used has a great effect on bacterial salt tolerance. Experiments on the effect of temperature on salt tolerance indicate that a temperature of 30 °C permits the greatest salt tolerance. In all of these experiments 0.375 and 1.37 M NaCl yielded the most rapid growth rates while 1.37 and 2.5 M NaCl permitted the greatest temperature tolerance. The Halomonas strain was found to have an absolute requirement for the Na+ cation. While NaNO3 and NaBr would substitute for NaCl in the growth medium, when LiCl, NH4Cl, MgCl2∙6H2O, or KCl was substituted for NaCl, the medium would not support growth. The bacterium consistently retained its rod shape regardless of the NaCl concentration in both complex and defined media. The data indicate that even though this bacterium has been in culture for over 5 years it is still well adapted to life in its natural environment.