Structure-dependent degradation of milk oligosaccharides by newly isolated intestinal commensal bacterial strains from suckling piglets and rabbits

Mammalian milk oligosaccharides serve as the first natural prebiotics for newborns, promoting the development of a beneficial gut microbiota. The ability of bacteria to use these complex sugars depends on their structure, but data are limited to bacteria isolated from newborn humans. This study aims to investigate in vitro the functional relationship between the structural variability of milk oligosaccharides and the metabolic capacities of newly intestinal commensal bacteria isolated from suckling rabbits and piglets. A total of 240 anaerobic intestinal bacterial strains were isolated from suckling piglets and rabbits, and 9 strains were cultivated in the presence of structurally different milk oligosaccharides: lacto-N-tetraose, 2'-fucosyllactose, and 3'-sialyllactose or 6'-sialyllactose. Five strains, belonging to Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides sp. D2, Bacteroides sp. 3₁₃3FAA and Phocaeicola vulgatus were able to utilize milk oligosaccharides. Growth curves revealed that glucose supported faster growth, while, leading to a lower final biomass compared to milk oligosaccharides. Both the growth rate and the final bacterial biomass varied depending on the milk oligosaccharide structure, with higher final biomass reached with 2'-fucosyllactose. The consumption rates of milk oligosaccharides exceeded 40% for all oligosaccharides in B. fragilis, Bacteroides sp. 3₁₃3FAA and P. vulgatus strains. Conversely, B. thetaiotaomicron with 6'-sialyllactose and Bacteroides sp. D2 strains for each milk oligosaccharide displayed a consumption rate below 40%. Milk oligosaccharide fermentation generated a more diverse metabolome compared to glucose. Utilization of milk oligosaccharides increased the production of propionate, isobutyrate, isovalerate, 2-methylbutyrate and 1, 2-propanediol. Remarkably, fermentation of 2'-fucosyllactose resulted in substantial 1, 2-propanediol production. Whole genome sequencing of the bacterial strains revealed the presence of diverse glycoside hydrolase in the strains capable of metabolizing milk oligosaccharides. This study demonstrates the capacity of diverse intestinal commensal bacteria from suckling rabbits and piglets to ferment diverse milk oligosaccharide structures, revealing species-specific and milk oligosaccharide structure-dependent metabolization profiles. These findings highlight the potential application of milk oligosaccharides as prebiotic supplements to support gut health in farm animals.