The implication of YggT of Escherichia coli in osmotic regulation.

An Escherichia coli mutant lacking three major K(+) uptake systems, Trk, Kup, and Kdp, did not grow under low K(+)and high Na(+) concentrations. The introduction of fkuA and of fkuB of a marine bacterium, Vibrio alginolyticus, has been reported to compensate for the growth defect by accelerating the rate of K(+) uptake (Nakamura, Katoh, Shimizu, Matsuba, and Unemoto, Biochim. Biophys. Acta, 1277, 201-208 (1996)). We investigated the function of unknown genes of E. coli, yggS and yggT, homologs of fkuA and fkuB respectively. E. coli TK2420 cells, which lack the three K(+) uptake systems, did not grow under high Na(+) or mannitol concentrations. The growth defect was compensated by the introduction of the yggT gene alone: yggS was not required. Here we found that YggT endowed E. coli cells with a tolerance for osmotic shock, and discuss a possible mechanism.