A transport system for phosphoenolpyruvate, 2-phosphoglycerate, and 3-phosphoglycerate in Salmonella typhimurium

Abstract

Salmonella typhimurium strain LT-2 was found to utilize phosphoenolpyruvate, 2-phosphoglycerate, and 3-phosphoglycerate as sole sources of carbon and energy for growth, but Escherichia coli strains did not. The following evidence suggests that this growth difference was due to the presence in Salmonella cells of an inducible phosphoglycerate permease distinct from previously studied transport systems: (a) The ability of cells to take up 3-phospho[14-C]glycerate was induced by growth in the presence of phosphoenolpyruvate, 2-phosphoglycerate, or 3-phosphoglycerate, but not glycerate, alpha-glycerophosphate, or other carbon sources tested. (b) Uptake of 3-phospho[14-C]glycerate was strongly inhibited by the three nonradioactive inducers of 3-phosphoglycerate uptake, but not by glycerate or alpha-glycerophosphate. (c) Mutants which lost the ability to utilize and take up 3-phosphoglycerate simultaneously lost the ability to utilize 2-phosphoglycerate and phosphoenolpyruvate, but not other compounds tested. (d) Mutant strains which constitutively synthesized the phosphoglycerate transport system could use both phosphoglycerates and phosphoenolpyruvate as sole sources of phosphate at low substrate concentrations. (e) A strain lacking alkaline and acid phosphatases could still grow with 3-phosphoglycerate as sole carbon source. Maximal rates of 3-phospho[14-C]glycerate uptake occurred at pH 6 in the presence of an exogenous energy source. The apparent Km for 3-phosphoglycerate uptake under these conditions was about 10-minus 4 M. The maximal uptake rate (but not the Km) was dependent on potassium ions. Although synthesis of the phosphoglycerate transport system appeared to be under adenosine 3:5-monophosphate control, glucose repressed induction only slightly. The genes controlling synthesis of the phosphoglycerate transport system (pgt genes) appeared to map at about 74 min on the Salmonella chromosome.