Different strategies of osmoadaptation in the closely related marine myxobacteria SWB007 and SIR-1.

Only a few myxobacteria are known to date that are classified as marine, owing to their salt dependency. In this study, the salt tolerance mechanism of these bacteria was investigated. To this end, a growth medium was designed in which the mutated strain BKA13 served as sole food source for the predatory, heterotrophic myxobacteria. This enabled measurement of the osmolytes without any background and revealed that the closely related strains SWB007 and SIR-1 developed different strategies to handle salt stress. SIR-1, which was grown between 1 and 4 % NaCl, relies solely on the accumulation of amino acids, while SWB007, which was grown between 0.5 and 3 % NaCl, employs, besides betaine, hydroxyectoine as the major compatible solute. In accordance with this analysis, only in the latter strain was a locus identified that codes for genes corresponding to the biosynthesis of betaine, ectoine and hydroxyectoine.