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Iron starvation in Bifidobacterium breve UCC2003 increases bile resistance through enhanced expression of a bile salt hydrolase

ABSTRACT: Bifidobacterium are considered to be beneficial for human health and are classified as probiotic bacterium. They must resist many environmental stress factors in order to survive in the gastrointestinal environment including; pH, oxygen availability, bile and nutrient starvation (eg: iron or carbon). This study investigates Bifidobacterium breve UCC2003 global genome response to growth under ferrous and/or ferric iron limiting conditions. Revealing that growth under iron limitation effects many processes in the cell including carbon and nitrogen metabolism and induces/reduces the expression of numerous genes; including multiple iron uptake systems, DPS proteins (which are predicted to be involved in iron storage/DNA protection), Fe-S cluster associated proteins and a bile salt hydrolase (bshB). Insertional mutagenesis and survival assays were employed and demonstrated that iron starvation imposed on B. breve UCC2003 results in an increased resistance to bile stress due to in part the iron-inducible transcription of the bshB gene. Furthermore, this study links BSH activity in B. breve UCC2003 to its ability to survive the deleterious effects of bile salt and suggest that B. breve UCC2003 may be use iron as a signal to adapt to the constantly changing environment within the small intestine.

ORGANISM(S): Bifidobacterium breve UCC2003

PROVIDER: GSE110080 | GEO | 2018/03/31

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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Iron starvation in Bifidobacterium breve UCC2003 increases bile resistance through enhanced expression of a bile salt hydrolase

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