A prominent role for glucosylglycerol in the adaptation of Pseudomonas mendocina SKB70 to osmotic stress.

The mechanism of osmoadaptation in a salt-tolerant (1.2 M NaCl) bacterial isolate identified as Pseudomonas mendocina (N. J. Palleroni, M. Doudoroff, R. Y. Stanier, R. E. Solanes, and R. Mandel, J. Gen. Microbiol. 60:215-231, 1970) was investigated. In response to osmotic stress, this species accumulated a number of compatible solutes, the intracellular levels of which depended on both the osmolarity and the ionic composition of the growth medium. Glucosylglycerol [alpha-D-glucopyranosyl-alpha-(1-->2)-glycerol], N-acetylglutaminylglutamine amide, and L-alpha-glutamate were the major compatible solutes accumulated via de novo biosynthesis. Trehalose was also accumulated, but only in cells grown in the presence of high concentrations of sulfate or phosphate ions. Glycine betaine was accumulated only when supplied exogenously to cells grown at high osmolarity, and its accumulation caused a significant depletion of the intracellular pools of glucosylglycerol and glutamate. Glucosylglycerol was also found to accumulate in the type strains of P. mendocina and P. pseudoalcaligenes. This is the first report demonstrating the pivotal role of glucosylglycerol in osmoadaptation in a nonphotosynthetic microorganism.