Identification and functional characterisation of cellobiose and lactose transport systems in Lactococcus lactis IL1403

Physiological, biochemical and macroarray analyses of Lactococcus lactis IL1403 and its ccpA and bglR single and double mutants engaged in lactose and β-glucosides catabolism were performed. The kinetic analysis indicated the presence of different transport systems for salicin and cellobiose. The control of salicin catabolism was found to be mediated by the transcriptional regulator BglR and the CcpA protein. The transcriptional analysis by macroarray technology of genes from the PEP:PTS regions showed that several genes, like ybhE, celB, ptcB and ptcA, were expressed at higher levels both in wild type cells exposed to cellobiose and in the ccpA mutant. We also demonstrated that in L. lactis IL1403 cultured on medium with cellobiose and lactose as carbon sources, after the first phase of cellobiose consumption and then co-metabolism of the two sugars, when cellobiose is exhausted the strain uses lactose as the only carbon source. These data could indicate that lactose and cellobiose are transported by a unique system—a PTS carrier induced by the presence of cellobiose, and negatively controlled by the CcpA regulator.