Metabolism of a plant derived galactose-containing polysaccharide by Bifidobacterium breve UCC2003

In this study, we describe the functional characterization of the Bifidobacterium breve UCC2003 gal locus, which is dedicated to the utilization of galactan, a plant-derived polysaccharide. Using a combination of molecular approaches we conclude that the galA gene of B. breve UCC2003 encodes a β-1,4-endogalactanase producing galacto-oligosaccharides, which are specifically internalized by an ABC transport system, encoded by galBCDE, and which are then hydrolysed to galactose moieties by a dedicated intracellular β-galactosidase, specified by galG. The generated galactose molecules are presumed to be fed into the fructose-6-phosphate phosphoketolase pathway via the Leloir pathway, thereby allowing B. breve UCC2003 to use galactan as its sole carbon and energy source. In addition to these findings we demonstrate that GalR is a LacI-type DNA-binding protein, which not only appears to control transcription of the galCDEGR operon, but also that of the galA gene.