Plant Glycan Metabolism by Bifidobacteria

Abstract

Members of the genus Bifidobacterium, of which the majority have been isolated as gut commensals, are Gram-positive, non-motile, saccharolytic, non-sporulating, anaerobic bacteria. Many bifidobacterial strains are considered probiotic and therefore are thought to bestow health benefits upon their host. Bifidobacteria are highly abundant among the gut microbiota of healthy, full term, breast-fed infants, yet the relative average abundance of bifidobacteria tends to decrease as the human host ages. Because of the inverse correlation between bifidobacterial abundance/prevalence and health, there has been an increasing interest in maintaining, increasing or restoring bifidobacterial populations in the infant, adult and elderly gut. In order to colonize and persist in the gastrointestinal environment, bifidobacteria must be able to metabolise complex dietary and/or host-derived carbohydrates, and be resistant to various environmental challenges of the gut. This is not only important for the autochthonous bifidobacterial species colonising the gut, but also for allochthonous bifidobacteria provided as probiotic supplements in functional foods. For example, Bifidobacterium longum subsp. longum is a taxon associated with the metabolism of plant-derived poly/oligosaccharides in the adult diet, being capable of metabolising hemicellulose and various pectin-associated glycans. Many of these plant glycans are believed to stimulate the metabolism and growth of specific bifidobacterial species and are for this reason classified as prebiotics. In this review, bifidobacterial carbohydrate metabolism, with a focus on plant poly-/oligosaccharide degradation and uptake, as well as its associated regulation, will be discussed.

Consistent Prebiotic Effects of Carrot RG-I on the Gut Microbiota of Four Human Adult Donors in the SHIME® Model despite Baseline Individual Variability

“…The released oligo-and monosaccharides could further be then scavenged by Bifidobacteriaceae that indeed are capable of fermenting arabinans and galactans [60,61], both side chains of cRG-I [26]. While likely not being the primary degraders, the consistent increase of Bifidobacteriaceae species in this or preceding studies [27], along with the well-documented health effects of members of this family [15], support the health-promoting potential of cRG-I fermentation by the human gut microbiota.…”

“…Moreover, this is also in agreement with the conclusion of Kelly et al that the complexity of pectin is likely too high for Bifidobacteriaceae, rendering them dependent on the initial degradation of these large polymers by Bacteroides sp. [15]. The released oligo-and monosaccharides could further be then scavenged by Bifidobacteriaceae that indeed are capable of fermenting arabinans and galactans [60,61], both side chains of cRG-I [26].…”

“…Among the hundreds of gut microbes, Bacteroides species display diverse and versatile glycan metabolising capabilities, allowing them to ferment extremely complex glycans [11][12][13][14], with other members such as Bifidobacterium species growing on the polysaccharide degradation products and metabolites [15]. In contrast to the beneficial effect of fiber fermentation, fermentation of amino acids results in the formation of potentially detrimental compounds (e.g., phenols, cresol, and hydrogen sulfide), contributing to IBD or colon cancer [16].…”

Phylogenomic disentangling of the Bifidobacterium longum subsp. infantis taxon

“…Our data therefore suggest that B. longum subsp. longum plays an ecological role in the metabolism of dietary, plant-derived carbohydrates during weaning and postweaning phases when infants are gradually introduced to a solid diet containing such complex carbohydrates [80][81][82]). Accordingly, the identified fermentation capabilities may provide an explanation as to how B. longum subsp.…”

Dietary fibre complexity and its influence on functional groups of the human gut microbiota

“…Within the other Gram-positive phylum that is commonly detected in the human gut, the Actinobacteria, most research has been carried out on Bifidobacterium species. There is diversity in which types of fibre are utilised by different species, but many species appear to be adapted to utilise mainly oligosaccharides or monosaccharides rather than complex insoluble fibre, and some species utilise host-derived carbohydrates (6,44,45) . Furthermore, resistant starch-degrading species such as B. adolescentis have also been reported (21,41) .…”