Abstract
Bifidobacterium longum subsp. infantis is a common member of the intestinal microbiota in breast-fed infants and capable of metabolizing human milk oligosaccharides (HMO). To investigate the bacterial response to different prebiotics, we analyzed both cell wall associated and whole cell proteins in B. infantis. Proteins were identified by LC-MS/MS followed by comparative proteomics to deduce the protein localization within the cell. Enzymes involved in the metabolism of lactose, glucose, galactooligosaccharides, fructooligosaccharides and HMO were constitutively expressed exhibiting less than two-fold change regardless of the sugar used. In contrast, enzymes in N-Acetylglucosamine and sucrose catabolism were induced by HMO and fructans, respectively. Galactose-metabolizing enzymes phosphoglucomutase, UDP-glucose 4-epimerase and UTP glucose-1-P uridylytransferase were expressed constitutively, while galactokinase and galactose-1-phosphate uridylyltransferase, increased their expression three fold when HMO and lactose were used as substrates for cell growth. Cell wall-associated proteomics also revealed ATP-dependent sugar transport systems associated with consumption of different prebiotics. In addition, the expression of 16 glycosyl hydrolases revealed the complete metabolic route for each substrate. Mucin, which possesses O-glycans that are structurally similar to HMO did not induced the expression of transport proteins, hydrolysis or sugar metabolic pathway indicating B. infantis do not utilize these glycoconjugates.
Highlights
Bifidobacterium longum subsp. infantis (B. infantis) is a common member of the gastrointestinal tract (GIT) of breast-fed infants [1]
Genome sequencing showed that B. infantis has a 40 kb gene cluster, termed human milk oligosaccharides (HMO) cluster I, that encodes several enzymes and transport systems required for HMO catabolism including afucosidase, a-sialidase, b-hexosaminidase, b-galactosidase and the ABC transport systems with six family 1, extracellular solute binding proteins (SBPs) predicted to bind oligosaccharides [11]
Mass spectrometry analysis of whole cell proteins is a common method to directly obtain information on the existing proteins within a biological system enabling the prediction of active metabolic pathways or regulatory networks
Summary
Bifidobacterium longum subsp. infantis (B. infantis) is a common member of the gastrointestinal tract (GIT) of breast-fed infants [1]. Genome sequencing showed that B. infantis has a 40 kb gene cluster, termed HMO cluster I, that encodes several enzymes and transport systems required for HMO catabolism including afucosidase, a-sialidase, b-hexosaminidase, b-galactosidase and the ABC transport systems with six family 1, extracellular solute binding proteins (SBPs) predicted to bind oligosaccharides [11]. These clusters of HMO-linked genes suggested a broader evolutionary partnership among B. infantis, the developing infant and human milk [12]
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