Carbohydrate metabolism in Bifidobacteria

Members of the genus Bifidobacterium can be found as components of the gastrointestinal microbiota, and are believed to play an important role in maintaining and promoting human health by eliciting a number of beneficial properties. Bifidobacteria can utilize a diverse range of dietary carbohydrates that escape degradation in the upper parts of the intestine, many of which are plant-derived oligo- and polysaccharides. The gene content of a bifidobacterial genome reflects this apparent metabolic adaptation to a complex carbohydrate-rich gastrointestinal tract environment as it encodes a large number of predicted carbohydrate-modifying enzymes. Different bifidobacterial strains may possess different carbohydrate utilizing abilities, as established by a number of studies reviewed here. Carbohydrate-degrading activities described for bifidobacteria and their relevance to the deliberate enhancement of number and/or activity of bifidobacteria in the gut are also discussed in this review.     

Carbohydrate metabolism in Agrobacterium tumefaciens

The activity of pentose cycling (PC) reactions in Agrobacterium tumefaciens is much greater than that normally found in bacteria, and in this regard the organism represents a unique category. Equations specifically derived from radiorespirometric data for bacteria with high PC activity in the presence of an alternate pathway are presented. A. tumefaciens utilizes d-glucose by strictly aerobic mechanisms involving the Entner-Doudoroff (ED) and PC pathways; relative participation by the ED pathway is 55% and by the PC cycle, 44%. The 3-ketoglycose-synthesizing system in the bacterium does not affect the relative participation of these two pathways. Radiorespirometric and enzymatic analyses clearly demonstrate that the Embden-Meyerhof-Parnas pathway does not function. Studies on the oxidation of pyruvic, acetic, succinic, and glutamic acids show that terminal respiration includes both the tricarboxylic acid and glyoxylic acid cycles.     

Carbohydrate moieties in human secretory component.

Human secretory component has seven putative sites for N-linked glycosylation. From tryptic and Glu-C digests we have isolated peptides encompassing asparagines 65, 72, 117, 168, 403, 451 and 481. Analysis by on line HPLC-electrospray mass spectrometry indicated that these residues were fully glycosylated and that the major carbohydrate moieties were far less diversified in composition than expected. Fast atom bombardment mass spectrometry performed on oligosaccharides released by peptide-N-glycosidase F treatment of fractionated and unfractionated SC digests showed the following glycan compositions: Fuc(2)Hex(5)HexNAc(4), Fuc(3)Hex(5)HexNAc(4), NeuAcFucHex(5)HexNAc(4), NeuAcFuc(2)Hex(5)HexNAc(4), NeuAc(2)Hex(5)HexNAc4 and NeuAc(2)FucHex(5)HexNAc(4). Three of these oligosaccharides are the major carbohydrate moieties in human lactoferrin. A possible biological role of the secretory component glycans in the protection of mucosal surfaces is discussed.