Evidence for the presence of two distinct phosphoenolpyruvate: Mannose phosphotransferase systems in Streptococcus mutans GS5-2

We have isolated a spontaneous 2-deoxyglucose (2DG) resistant mutant from Streptococcus mutans GS5-2, called GM500, that grew as well as the parental strain on mannose. Membranes of glucose-grown cells of the mutant strain were, however, unable to catalyse the phosphoenolpyruvate-dependent phosphorylation of mannose in the presence of purified enzyme I (EI) and hydroxyproline (HPr) unlike the wild-type cells. Resting cells of strain GM500 were also unable to transport mannose after growth at the expense of glucose, whereas glucose-grown cells of strain GS5-2 transported and metabolized mannose at a high rate. These activities were recovered in the mutant strain after growth on mannose. Our results indicate the presence of 2 phosphoenolpyruvate:mannose phosphotransferase systems in S. mutans GS5-2. One system was constitutive and had a Ks for mannose of 2.6 μM. The other system was inducible with a Ks for mannose of 15 μM.