Role of trehalose in growth at high temperature of Salmonella enterica serovar typhimurium

Moderate osmolality can stimulate bacterial growth at temperatures near the upper limit for growth. We investigated the mechanism by which high osmola lity enhances the thermotolerance of Salmonella enterica serovar Typhimuriu m, by isolating bacteriophage MudI1734-induced insertion mutations that blo cked the growth-stimulatory effect of 0.2 M NaCl at 45 degreesC, One of the se mutations proved to be in the seqA gene (a regulator of initiation of DN A synthesis). Because this gene is cotranscribed with pgm (which encodes ph osphoglucomutase), it is likely to be polar on the expression of the pgm ge ne. Pgm catalyzes the conversion of glucose-6-phosphate to glucose-1-phosph ate during growth on glucose, and therefore loss of Pgm results in a defici ency in a variety of cellular constituents derived from glucose-1-phosphate , including trehalose, To test the possibility that the growth defect of th e seqA::MudI1734 mutant at high temperature in medium of high osmolality is due to the block in trehalose synthesis, we determined the effect of an ot sA mutation, which inactivates the first step of the trehalose biosynthetic pathway. The otsA mutation caused a growth defect at 45 degreesC in minima l medium containing 0.2 M NaCl that was similar to that caused by the pgm m utation, but otsA did not affect growth rate in this medium at 37 degreesC. These results suggest that the growth defect of the seqA-pgm mutant at hig h temperature could be a consequence of the block in trehalose synthesis. W e found that, in addition to the well-known osmotic control, there is a tem perature dependent control of trehalose synthesis such that, in medium cont aining 0.2 M NaCl, cells grown at 45 degreesC had a fivefold higher trehalo se pool size than cells grown at 30 degreesC. Our observations that trehalo se accumulation is thermoregulated and that mutations that block trehalose synthesis cause a growth defect at high temperature in media of high osmola lity suggested that this disaccharide is crucial for growth at high tempera ture either for turgor maintenance or for protein stabilization.