A bile-inducible membrane protein mediates bifidobacterial bile resistance.
Bottom Line: The high level of similarity to bile efflux pumps from other bifidobacteria suggests a significant and general role for Bbr_0838 in bile tolerance.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) .This study represents the first in-depth analysis of a bile-inducible locus in bifidobacteria, identifying a key gene relevant for bifidobacterial bile tolerance.
Affiliation: Departamento de Microbiología y Bioquímica de Productos Lácteos, Instituto de Productos Lácteos de Asturias, Villaviciosa, Asturias, Spain.Show MeSH
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Mentions: To examine the effect of the Bbr_0838 mutation on bile tolerance, a series of survival and growth experiments were carried out in MRSc supplemented with ox‐gall, or particular components of bile. The minimal inhibitory concentrations of a complex mixture of bile salts, ox‐gall and individual bile salts, were determined during 24 h growth experiments. The main bile acids in humans are represented by glycocholate and taurocholate, while bile acids resulting from metabolism of bile in the intestine, are represented by cholate, and deoxycholate. Differences in MIC between both strains were only detected in MRSc supplemented with cholate, where a MIC value of 0.2% (w/v) was observed for the wild‐type strain, while the UCC2003::838800mutant was more sensitive with a corresponding MIC value of 0.1% (w/v). MICs were identical for ox‐gall (> 10%), glycocholate (0.25%), taurocholate (> 1%) and glycodeoxycholate (0.625%). This is in accordance with our recent results, in which maximum transcriptional induction levels of Bbr_0838 were observed in the presence of cholate (Ruiz et al., 2011) and were further substantiated by growth experiments. In the presence of 0.025%, 0.05% or 0.1% (w/v) of cholate, UCC2003::838800exhibited slower growth and a lower final OD at 600 nm after 24 h, as compared with UCC2003 (Fig. 3). Enumeration of viable cells in overnight cultures by plate counts and Dead/Live labelling also pointed to reduced growth and cell viability of UCC2003::838800 grown in the presence of cholate (data not shown).
Affiliation: Departamento de Microbiología y Bioquímica de Productos Lácteos, Instituto de Productos Lácteos de Asturias, Villaviciosa, Asturias, Spain.