Metabolism of betaine as a carbon source by an osmotolerant bacterium isolated from the weed rhizosphere

An isolate of an osmotolerant rhizobacterium has been obtained from a weed rhizosphere which showed tolerance up to 1.0 M NaCl. The isolate has been subjected to growth analysis in a medium which contained 10 mM betaine as the sole carbon source. It was observed that betaine could be used as the sole carbon source for the growth of salt-tolerant rhizobacteria under NaCl-stress at 1.0 M concentration. Interestingly, it was found that betaine at 100 mM concentration suppressed the growth of salt-tolerant rhizobacteria. The growth of the osmotolerant rhizobacterium was stimulated when it was grown in a medium containing both glucose and betaine, demonstrating that betaine was an osmoprotectant. The presence of glucose at 10 mM concentration, however, did not alleviate the growth-suppressive effect of betaine at 100 mM concentration. The osmoprotective effect of betaine was demonstrated by the fact that the addition of betaine at different time intervals enhanced the growth accordingly. However, the growth-suppressive effect of betaine at 100 mM concentration was also noticeable when betaine was added at different time intervals.