Bacterial exopolysaccharides (EPSs) are mono- or oligo-saccharide units linked by glycosidic bonds, forming homo- or hetero-polymers. In gut commensals, these macromolecules are claimed to protect bacterial cells against gastrointestinal challenges and to be involved in modulating the cross talk between the producing bacterium and its gut environment. The predicted EPS arsenal of theBifidobacteriumgenus, which we designate here as theeps-ome, consists of 9epsgene clusters conserved among different bifidobacterial species and a further 44 uniqueepsloci, together representing a large proportion of the inter(sub)species variability identified among bifidobacterial genomes. Co-cultivations of bifidobacterial species in media simulating adult and infant human gut environments resulted in an increased transcription of key genes for EPS biosynthesis, including glycosyltransferase-encoding genes, as well as genes specifying EPS transporter and polymerase functions, and saccharide biosynthesis and modification enzymes.