Metabolism of human milk oligosaccharides by infant-associated bifidobacteria

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dc.contributor.advisor van Sinderen, Douwe en
dc.contributor.author James, Kieran
dc.date.accessioned 2018-05-14T10:40:18Z
dc.date.issued 2018
dc.date.submitted 2018
dc.identifier.citation James, K. 2018. Metabolism of human milk oligosaccharides by infant-associated bifidobacteria. PhD Thesis, University College Cork. en
dc.identifier.endpage 266 en
dc.identifier.uri http://hdl.handle.net/10468/6097
dc.description.abstract Bifidobacteria are Gram-positive, anaerobic bacteria belonging to the Actinobacteria phylum, and are commensals of the mammalian, avian and occasionally insect gastrointestinal tracts. In humans, bifidobacteria are typically highly abundant in the intestinal microbiota of healthy breastfed infants, in particular a small number of infant-associated species, including Bifidobacterium breve, Bifidobacterium longum subsp. infantis, Bifidobacterium bifidum and Bifidobacterium kashiwanohense. A key adaptation, facilitating the establishment and dominance of these species in the breastfed infant gut microbiota, is the ability to consume and metabolise specific glycans only found in breastmilk, and indigestible for the infant, known as Human Milk Oligosaccharides (HMOs). Fascinatingly, the adaptation to utilise HMO as a substrate by bifidobacteria is almost exclusively reserved for infant-associated species, and even more fascinatingly, these species have developed strikingly varying strategies for the consumption of different HMO components. Strategies for the metabolism of various individual HMO glycans in different species of bifidobacteria shall be discussed in this thesis, with particular focus on B. breve UCC2003 and the novel isolate B. kashiwanohense APCKJ1. Chapter II of this thesis is comprised of work elucidating the mechanisms and components of LNT, LNnT and LNB utilisation pathways in Bifidobacterium breve UCC2003. Using a combination of experimental approaches, the enzymatic machinery involved in the metabolism of LNT, LNnT and LNB is identified and characterised. Furthermore, the distribution across the genus, of homologs for the key genes involved in the utilisation of these substrates, is analysed. Chapter III focuses on identifying the regulatory network responsible for the transcriptional control of the genes involved in LN(n)T and LNB metabolism, as described in Chapter II. Three transcriptional regulators and corresponding operator and associated (inducible) promoter sequences are characterised, the latter governing transcription of the genetic elements involved in LN(n)T/LNB metabolism. Furthermore, identification of the transcriptional effectors reveals the presence of a series of positive-feedback loops, inducing expression in the presence of breakdown products of key HMO-derived metabolites. In Chapter IV, Bifidobacterium isolates are obtained by screening a number of faecal samples from breastfed infants, using HMO components fucosyllactose and sialyllactose as selective carbohydrates, and compared with isolates obtained using lactose or GOS. A range of bifidobacterial species were obtained, varying between the selective carbohydrate used, and supporting the notion of selective HMO consumption. Analysis of the glycosyl hydrolase profiles of representative strains of the species obtained reveals interesting correlations with their preferential carbohydrate-based selection. In Chapter V, a novel B. kashiwanohense isolate, APCKJ1, which was isolated in the work of Chapter IV, is demonstrated to consume fucosyllactose, and the mechanisms of its utilisation of both fucosyllactose and L-fucose is examined. Using a combination of approaches, the main cellular machinery involved in the uptake and degradation of fucosyllactose is characterised, and heterologous expression of these genes in a B. breve UCC2003 host reveals not only the mechanisms of the utilisation of fucosyllactose, but a potentially functional pathway for the catabolism of fucose, in both strains. The work presented in this thesis represents novel information on the metabolism of HMO glycans in bifidobacteria, particularly in the species B. breve and B. kashiwanohense, as well as key insights into the strategies of HMO utilisation by infant-associated bifidobacteria in general, as an adaptation to the GIT of breastfed infants. en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2018, Kieran James. en
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/3.0/ en
dc.subject Microbiology en
dc.subject Probiotics en
dc.subject Prebiotics en
dc.subject Bifidobacteria en
dc.subject Infant Health en
dc.subject Human milk oligosaccharides en
dc.subject Carbohydrate metabolism en
dc.subject Molecular biology en
dc.title Metabolism of human milk oligosaccharides by infant-associated bifidobacteria en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD en
dc.internal.availability Full text available en
dc.description.version Accepted Version
dc.contributor.funder Irish Research Council for Science, Engineering and Technology en
dc.description.status Not peer reviewed en
dc.internal.school Microbiology en
dc.check.reason This thesis contains data which has not yet been published en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.embargoformat Apply the embargo to both hard bound copy and e-thesis (If you have submitted an e-thesis and a hard bound thesis and want to embargo both) en
ucc.workflow.supervisor d.vansinderen@ucc.ie
dc.internal.conferring Summer 2018 en
dc.internal.ricu APC Microbiome Institute en


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