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Transcriptional and Functional Characterization of genetic elements involved in galacto-oligosaccharide utilisation by Bifidobacterium breve UCC2003

ABSTRACT: It is increasingly recognised that the gastrointestinal microbiota plays a critical role in human health and promising evidence is accumulating that with dietary strategies, of prebiotic intervention, microbiota imbalances can be corrected and host health improved. Several prebiotics are widely used commercially in foods including inulin, fructo-oligosaccharides, galacto-oligosaccharides and resistant starches and there is convincing evidence, in particular for galacto-oligosaccharides, that prebiotics can modulate the microbiota and promote the growth of bifidobacteria in the intestinal tract of infants and adults. In this study we describe the identification and functional characterisation of the genetic loci responsible for the transport and metabolism of purified galacto-oligosaccharides (PGOS) by our model bifidobacterial strain, B. breve UCC2003. We further demonstrate that the extracellular endogalactanase specified by several B. breve strains, including B. breve UCC2003, is essential for metabolism of PGOS components with a long retention time and high degree of polymerisation. These PGOS components are transported into the bifidobacterial cell via various ABC transport systems and sugar permeases where they are further metabolised to galactose and glucose monomers that feed into the bifid shunt. This research described here advances our understanding of GOS metabolism by bifidobacteria and for the future there is great potential for exploiting bifidobacterial beta-galactosidase to create targeted prebiotics that can enrich for selected Bifiobacteria sp. and other beneficial microbes among the gut microbiota.

ORGANISM(S): Bifidobacterium breve UCC2003

PROVIDER: GSE37214 | GEO | 2014/12/31

SECONDARY ACCESSION(S): PRJNA158941

REPOSITORIES: GEO

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Project description:Bbr_0838 from Bifidobacterium breve UCC2003 encodes a 683 residue membrane protein, that contains a permease domain displaying similarity to transporters belonging to the major facilitator superfamily, as well as a CBS (cystathionine beta synthase) domain. The high level of similarity to bile-efflux pumps from other bifidobacteria, suggests a significant role for Bbr_0838 in bile tolerance of B. breve UCC2003. Bbr_0838 transcription was shown to be monocistronic and strongly induced upon exposure to bile. Further analysis delineated the transcriptional start site and the minimal region required for promoter activity and bile regulation. Insertional inactivation of Bbr_0838 in B. breve UCC2003 resulted in a strain that exhibited reduced survival upon cholate exposure as compared to the parent strain, a phenotype that was reversed when a functional Bbr_0838 gene was introduced into UCC2003::838800. Transcriptome analysis of UCC2003::838800 grown in the presence or absence of bile demonstrated that transcription of Bbr_0832, which is predicted to encode a macrolide-efflux transporter gene, was significantly increased in the presence of bile, representing a likely compensatory mechanism for bile removal in the absence of Bbr_0838. This study represents the first in depth analysis of a bile-inducible locus in bifidobacteria, identifying a key gene relevant for bifidobacterial bile tolerance. In order to investigate differences in global gene expression upon growth or exposure of B. breve UCC2003-delta0838 to cholic acid compared to normal growing cells, DNA microarray experiments were performed. Total RNA was isolated from B. breve UCC2003-delta0838 cultures under normal conditions and cultures grown on or exposed to cholic acid. All experiments were performed in duplo and targets where confirmed with QRT-PCR. In addition transcriptome analyse was performed of B. breve UCC2003 compared to that of B. breve UCC2003-delta0838 both exposed to 0.1 % cholic acid. This was performed as a single experiment and targets were confirmed by QRT-PCR

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Transcriptional and Functional Characterization of genetic elements involved in galacto-oligosaccharide utilisation by Bifidobacterium breve UCC2003

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