Contribution of the phosphoenolpyruvate:mannose phosphotransferase system to carbon catabolite repression in Lactobacillus pentosus

The role of the Lactobacillus pentosus phosphoenolpyruvate :mannose phosphotransferase system (mannose PTS) in sugar transport and control of sugar utilization was investigated. Growth experiments and measurements of PEP-dependent phosphorylation of sugars, of sugar transport and of catabolic enzyme activity were performed, to compare a wild-type strain with an EIIBMan mutant, LPE6, and a ccpA mutant, LPE4. Fructose uptake in wild-type bacteria demonstrated the presence of two fructose-specific PTSs: a high-affinity system, EIIFru (K-m = 52 muM) which is inducible by fructose, and a low-affinity system (K-m = 300 muM), The latter system was racking in LPE6 and therefore corresponds to EIIMan. LPE6 was unable to phosphorylate glucose, mannose, N-acetylglucosamine and 2-deoxyglucose in a PEP-dependent reaction, indicating that these sugars are substrates of EIIMan. Transport and phosphorylation of these compounds was the same in LPE4 and in wild-type bacteria, although growth of LPE4 on these sugars was impaired. In wild-type bacteria and in LPE4 the activity of EIIFru was lowered by the presence of EIIMan substrates in the growth medium, but this decrease was not observed in LPE6. These results indicate that EIIMan but not CcpA regulates the synthesis of EIIFru. Mutations in EIIMan or CcpA resulted in a relief of catabolite repression exerted by EIIMan substrates on the activity of beta -galactosidase and beta -glucosidase, indicating that EIIMan and CcpA are important components in catabolite repression in L. pentosus. Fructose-mediated repression of these two enzymes appeared to be correlated with the activity of EIIFru.