ABSTRACTHuman milk contains a high concentration of complex oligosaccharides that influence the composition of the intestinal microbiota in breast-fed infants. Previous studies have indicated that select species such asBifidobacterium longumsubsp.infantisandBifidobacterium bifidumcan utilize human milk oligosaccharides (HMO)in vitroas the sole carbon source, while the relatively fewB. longumsubsp.longumandBifidobacterium breveisolates tested appear less adapted to these substrates. Considering the high frequency at whichB. breveis isolated from breast-fed infant feces, we postulated that someB. brevestrains can more vigorously consume HMO and thus are enriched in the breast-fed infant gastrointestinal tract. To examine this, a number ofB. breveisolates from breast-fed infant feces were characterized for the presence of different glycosyl hydrolases that participate in HMO utilization, as well as by their ability to grow on HMO or specific HMO species such as lacto-N-tetraose (LNT) and fucosyllactose. AllB. brevestrains showed high levels of growth on LNT and lacto-N-neotetraose (LNnT), and, in general, growth on total HMO was moderate for most of the strains, with several strain differences. Growth and consumption of fucosylated HMO were strain dependent, mostly in isolates possessing a glycosyl hydrolase family 29 α-fucosidase. Glycoprofiling of the spent supernatant after HMO fermentation by select strains revealed that allB. brevestrains can utilize sialylated HMO to a certain extent, especially sialyl-lacto-N-tetraose. Interestingly, this specific oligosaccharide was depleted before neutral LNT by strain SC95. In aggregate, this work indicates that the HMO consumption phenotype inB. breveis variable; however, some strains display specific adaptations to these substrates, enabling more vigorous consumption of fucosylated and sialylated HMO. These results provide a rationale for the predominance of this species in breast-fed infant feces and contribute to a more accurate picture of the ecology of the developing infant intestinal microbiota.
Phenotypic and Genomic Analyses of Human Strains Belonging or Related to Bifidobacterium longum, Bifidobacterium infantis, and Bifidobacterium breve
