Studies of the Listeria monocytogenes Cellobiose Transport Components and Their Impact on Virulence Gene Repression.

Background:Many bacteria transport cellobiose via a phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). InListeria monocytogenes, two pairs of soluble PTS components (EIIA(Cel1)/EIIBCel1 and EIIA(Cel2)/EIIBCel2) and the permease EIICCel1 were suggested to contribute to cellobiose uptake. Interestingly, utilization of several carbohydrates, including cellobiose, strongly represses virulence gene expression by inhibiting PrfA, the virulence gene activator.Results:The LevR-like transcription regulator CelR activates expression of the cellobiose-induced PTS operonscelB1-celC1-celA1,celB2-celA2, and the EIIC-encoding monocistroniccelC2. Phosphorylation by P similar to His-HPr at His550 activates CelR, whereas phosphorylation by P similar to EIIBCel1 or P similar to EIIBCel2 at His823 inhibits it. Replacement of His823 with Ala or deletion of bothcelAorcelBgenes caused constitutive CelR regulon expression. Mutants lacking EIICCel1, CelR or both EIIA(Cel) exhibitedslow cellobiose consumption. Deletion ofcelC1orcelRprevented virulence gene repression by the disaccharide, but not by glucose and fructose. Surprisingly, deletion of bothcelAgenes caused virulence gene repression even during growth on non-repressing carbohydrates. No cellobiose-related phenotype was found for thecelC2mutant.Conclusion:The two EIIA/B-Cel pairs are similarly efficient as phosphoryl donors in EIICCel1-catalyzed cellobiose transport and CelR regulation. The permanent virulence gene repression in thecelAdouble mutant further supports a role of PTSCel components in PrfA regulation.