title: A bile-inducible membrane protein mediates bifidobacterial bile resistance.
abstract: Bbr_0838 from Bifidobacterium breve UCC2003 is predicted to encode a 683 residue membrane protein, containing both a permease domain that displays 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 and general role for Bbr_0838 in bile tolerance. 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, UCC2003:838(800) , which exhibited reduced survival upon cholate exposure as compared with the parent strain, a phenotype that was reversed when a functional, plasmid-encoded Bbr_0838 gene was introduced into UCC2003:838(800) . Transcriptome analysis of UCC2003:838(800)  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.
authors.affiliation: Departamento de Microbiología y Bioquímica de Productos Lácteos, Instituto de Productos Lácteos de Asturias, Villaviciosa, Asturias, Spain.
authors.forename: Lorena
authors.initials: L
authors.lastname: Ruiz
authors.forename: Mary
authors.initials: M
authors.lastname: O'Connell-Motherway
authors.forename: Aldert
authors.initials: A
authors.lastname: Zomer
authors.forename: Clara G
authors.initials: CG
authors.lastname: de los Reyes-Gavilán
authors.forename: Abelardo
authors.initials: A
authors.lastname: Margolles
authors.forename: Douwe
authors.initials: D
authors.lastname: van Sinderen
mesh_terms: D001644:Bifidobacterium / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D001646:Bile / Q000378:metabolism*; D003902:Detergents / Q000633:toxicity*; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D050296:Microbial Viability / Q000187:drug effects; D016254:Mutagenesis, Insertional; D011401:Promoter Regions, Genetic; D024363:Transcription Initiation Site
chemical_list: D003902:Detergents; D008565:Membrane Proteins