The glucose permease of the phosphotransferase system of Bacillus subtilis: evidence for IIGlc and IIIGlc domains

Abstract

Glucose is taken up in Bacillus subtilis via the phosphoenolpyruvate:glucose phosphotransferase system (glucose PTS). Two genes, orfG and ptsX, have been implied in the glucose‐specific part of this PTS, encoding an Enzyme II^Glc and an Enzyme III^Glc, respectively. We now show that the glucose permease consists of a single, membrane‐bound, polypeptide with an apparent molecular weight of 80000, encoded by a single gene which will be designated ptsG. The glucose permease contains domains that are 40‐50% identical to the II^Glc and III^Glc proteins of Escherichia coli. The B. subtilis III^Glc domain can replace III^Glc in E. coli crr mutants in supporting growth on glucose and transport of methyl α‐glucoside. Mutations in the II^Glc and III^Glc domains of the B. subtilis ptsG gene impaired growth on glucose and in some cases on sucrose. ptsG mutants lost all methyl α‐glucoside transport but retained part of the glucose‐transport capacity. Residual growth on glucose and transport of glucose in these ptsG mutants suggested that yet another uptake system for glucose existed, which is either another PT system or regulated by the PTS. The glucose PTS did not seem to be involved in the regulation of the uptake or metabolism of non‐PTS compounds like glycerol. In contrast to ptsl mutants in members of the Enterobacteriaceae, the defective growth of B. subtilis ptsl mutants on glycerol was not restored by an insertion in the ptsG gene which eliminated II^Glc. Growth of B. subtilis ptsG mutants, lacking II^Glc, was not impaired on glycerol. From this we concluded that neither non‐phosphorylated nor phosphorylated II^Glc was acting as an inhibitor or an activator, respectively, of glycerol uptake and metabolism.