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The cell-envelope proteome of Bifidobacterium longum in an in vitro bile environment

¹ Instituto de Productos Lácteos de Asturias, Consejo Superior de Investigaciones Científicas (CSIC), Ctra Infiesto s/n, 33300, Villaviciosa, Asturias, Spain
² Biomedical Proteomics Research Group, Department of Structural Biology and Bioinformatics, University of Geneva, 1 Rue Michel Servet, 1211 Geneva 14, Switzerland
³ UMR 5248 CBMN, CNRS-Université Bordeaux 1-ENITAB, Laboratoire de Microbiologie et Biochimie Appliquée, 1 cours du Général de Gaulle, 33175 Gradignan CEDEX, France

Correspondence
Abelardo Margolles
amargolles{at}ipla.csic.es

Host–bacteria interactions are often mediated via surface-associated proteins. The identification of these proteins is an important goal of bacterial proteomics. To address how bile can influence the cell-envelope proteome of Bifidobacterium longum biotype longum NCIMB 8809, we analysed its membrane protein fraction using stable isotope labelling of amino acids in cell culture (SILAC). We were able to identify 141 proteins in the membrane fraction, including a large percentage of the theoretical transporters of this species. Moreover, the envelope-associated soluble fraction was analysed using different subfractionation techniques and differential in-gel fluorescence electrophoresis (DIGE). This approach identified 128 different proteins. Some of them were well-known cell wall proteins, but others were highly conserved cytoplasmic proteins probably displaying a ‘moonlighting’ function. We were able to identify 11 proteins in the membrane fraction and 6 proteins in the envelope-associated soluble fraction whose concentration varied in the presence of bile. Bile promoted changes in the levels of proteins with important biological functions, such as some ribosomal proteins and enolase. Also, oligopeptide-binding proteins were accumulated on the cell surface, which was reflected in a different tripeptide transport rate in the cells grown with bile. The data reported here will provide the first cell-envelope proteome map for B. longum, and may contribute to understanding the bile tolerance of these bacteria.

Three supplementary tables are available with the online version of this paper.

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