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

The role of the Lactobacillus pentosus phosphoenolpyruvate :mannose phospho transferase system (mannose PTS) in sugar transport and control of sugar ut ilization was investigated. Growth experiments and measurements of PEP-depe ndent phosphorylation of sugars, of sugar transport and of catabolic enzyme activity were performed, to compare a wild-type strain with an EIIBMan mut ant, LPE6, and a ccpA mutant, LPE4. Fructose uptake in wild-type bacteria d emonstrated the presence of two fructose-specific PTSs: a high-affinity sys tem, EIIFru (K-m = 52 muM) which is inducible by fructose, and a low-affini ty system (K-m = 300 muM), The latter system was racking in LPE6 and theref ore corresponds to EIIMan. LPE6 was unable to phosphorylate glucose, mannos e, N-acetylglucosamine and 2-deoxyglucose in a PEP-dependent reaction, indi cating that these sugars are substrates of EIIMan. Transport and phosphoryl ation of these compounds was the same in LPE4 and in wild-type bacteria, al though growth of LPE4 on these sugars was impaired. In wild-type bacteria a nd in LPE4 the activity of EIIFru was lowered by the presence of EIIMan sub strates in the growth medium, but this decrease was not observed in LPE6. T hese results indicate that EIIMan but not CcpA regulates the synthesis of E IIFru. Mutations in EIIMan or CcpA resulted in a relief of catabolite repre ssion exerted by EIIMan substrates on the activity of beta -galactosidase a nd beta -glucosidase, indicating that EIIMan and CcpA are important compone nts in catabolite repression in L. pentosus. Fructose-mediated repression o f these two enzymes appeared to be correlated with the activity of EIIFru.