Utilization of Host-Derived Glycans by Intestinal Lactobacillus and Bifidobacterium Species

Abstract

Members of the genus Lactobacillus are commonly found at the gastrointestinal tract and other mucosal surfaces of humans. This genus includes various species with a great number of potentially probiotic bacteria. Other often-used probiotic species belong to Bifidobacterium, a genus almost exclusively associated with the gut. As probiotics must survive and be metabolically active at their target sites, namely host mucosal surfaces, consumption of host-produced glycans is a key factor for their survival and activity. The ability to metabolize glycans such as human milk oligosaccharides (HMOs), glycosaminoglycans and the glycan moieties of glycoproteins and glycolipids found at the mucosal surfaces grants a competitive advantage to lactobacilli and bifidobacteria. The analyses of the great number of sequenced genomes from these bacteria have revealed that many of them encode a wide assortment of genes involved in the metabolism and transport of carbohydrates, including several glycoside hydrolases required for metabolizing the carbohydrate moieties of mucins and HMOs. Here, the current knowledge on the genetic mechanisms, known catabolic pathways and biochemical properties of enzymes involved in the utilization of host-produced glycans by lactobacilli and bifidobacteria will be summarized.

Role of Protein Glycosylation in Host-Pathogen Interaction

“…In animals, the glycoproteins facilitate the growth of probiotics in the gut thus provides a chemical barrier against pathogens [93]. The O-glycans of glycoproteins like MUC2 can serve as attachment sites for probiotic colonization [13,94] by providing favorable nutrition substances [95]. Consequently, intestinal surface harbors a complex ecosystem consisting of a myriad of intestinal microorganisms that affect the physiology, immune function, and fitness of the host [96].…”

Enzymatic Adaptation of Bifidobacterium bifidum to Host Glycans, Viewed from Glycoside Hydrolyases and Carbohydrate-Binding Modules

“…longum (B. longum), are frequently detected in the stool of breast-fed infants. Many studies [9][10][11][12][13][14][15][16][17][18][19] have indicated that the formation of a bifidus-flora in the gut of breast-fed infants can be attributed to human milk oligosaccharides (HMOs), which are the third most abundant solid component in breastmilk after lactose and lipids [20][21][22]. Mothers produce the energy-rich HMOs, even though HMOs have no direct nutritional value for infants, as HMOs are resistant to digestive enzymes secreted in the gastrointestinal tract.…”

Unique Microbial Catabolic Pathway for the Human Core N -Glycan Constituent Fucosyl-α-1,6- N -Acetylglucosamine-Asparagine

“…N-Glycosylated proteins are present at human mucosal surfaces and in breast milk (9,10,52), and therefore, they can be accessible to the gut microbiota. Most studies about energy sources for gut-beneficial microbes have been focused on carbohydrates present in the diet or added as prebiotics (53), whereas knowledge about the catabolism of host-derived carbon and nitrogen sources is scarce (16). We have demonstrated that L. casei is able to metabolize the glycoamino acid 6=FN-Asn, which is the core structure of the N-glycan sites of ␣1,6-fucosylated glycoproteins.…”

“…Protein N-glycosylation plays a crucial role in a variety of cellular processes, such as cell adhesion (13), immune pathway signaling (14), and bacterial recognition (15). Some intestinal microorganisms have the ability to process the carbohydrate moieties of N-glycosylated proteins (16) so that the type, abundance, and location of these glycans contribute to shaping the composition and distribution of the gut microbiota (17). Some bacterial pathogens possess endo-␤-N-acetylglucosaminidase enzymes that cleave the ␤-1,4 linkage of the core ChbNAc present in all N-glycoproteins, releasing the N-glycan moiety (18).…”