Increasing evidence suggests that isomaltooligosaccharides (IMO, α-1,6-linked glucosides) and panose exert a prebiotic effect by positively stimulating the growth of probiotics from the Lactobacillus and Bifidobacterium genera while reducing the levels of other gut commensals in the human gastrointestinal tract (1,2). Remarkably, the genetics and the enzymology of IMO utilisation in the gut niche remain virtually unexplored at the molecular level. We have used genomic and transcriptomic analyses to identify and analyse IMO utilisation loci in probiotic bifidobacteria and lactobacilli as typified by Lactobacillus acidophilus NCFM and Bifidobacterium animalis subsp. lactis B1-04 respectively. Interestingly, IMO utilisation was characterised by high diversity regarding uptake transporters, glycoside hydrolases (GHs), and co-occurrence of GHs with other specificities within the same loci. A phylogenetics and sequence motif analysis showed the enrichment of glucan α-1,6 glucosidases of GH13_31 in probiotic lactobacilli as compared to other taxonomic groups colonising the gut niche, thus indicating that these enzymes mediate the hydrolysis of longer IMO in this group of organisms, while bifidobacteria possessed other GH13 glucosidases active on MOs. The GH13_31 enzymes targeting IMO occurred frequently within maltooligosaccharide loci, suggesting a possible link between the metabolism of α-1,4 and of α-1,6 glucosides in this group of bacteria, while genes encoding GH13 IMO active enzymes were co-localised with GH36 α-galactosidases in several bifidobacteria together with a single ABC transporter, suggesting dual specificity of this transporter.
展开▼
