title: Bifidobacteria exhibit LuxS-dependent autoinducer 2 activity and biofilm formation.
abstract: Autoinducer-2 (AI-2) molecules are one class of signalling molecules involved in gene regulation dependent on population density in a mechanism commonly referred to as quorum sensing (QS). AI-2 is produced by the methylthioadenosine/S-adenosyl-homocysteine nucleosidase LuxS. In the present study, we characterise the function of bifidobacterial LuxS proteins to address the question whether these economically important bacteria are able to perform QS communication. All publically available genome sequences of bifidobacteria harbour putative luxS genes. The deduced amino acid sequences are well conserved in the genus and show good homology to the LuxS protein of the prototypical AI-2 producer Vibrio harveyi. The luxS genes of three bifidobacterial strains were successfully expressed in AI-2-negative Escherichia coli DH5α. Supernatants of these recombinant E. coli strains contained significant AI-2 activity. In initial experiments, we failed to detect AI-2 activity in supernatants of bifidobacteria grown in MRSc. High concentration of glucose as well as acidic pH had strong inhibitory effects on AI-2 activity. AI-2 activity could be detected when lower volumes of supernatants were used in the assay. Homologous overexpression of luxS in Bifidobacterium longum NCC2705 increased AI-2 levels in the supernatant. Furthermore, over-expression of luxS or supplementation with AI-2-containing supernatants enhanced biofilm formation of B. longum NCC2705. Collectively, these results suggest that bifidobacteria indeed harbour functional luxS genes that are involved in the production of AI-2-like molecules. To the best of our knowledge, this represents the first report on AI-2 activity produced by bifidobacteria. Self-produced AI-2 activity as well as AI-2-like molecules of other bacteria of the intestinal tract may have a regulatory function in biofilm formation and host colonization by bifidobacteria.
authors: Institute of Microbiology and Biotechnology, University of Ulm, Ulm, Germany.
authors: Zhongke
authors: Z
authors: Sun
authors: Institute of Disease Control and Prevention, Academy of Military Medical Sciences, Beijing, China.
authors: Xiang
authors: X
authors: He
authors: Institute of Microbiology and Biotechnology, University of Ulm, Ulm, Germany.
authors: Vincenzo F
authors: VF
authors: Brancaccio
authors: Institute of Disease Control and Prevention, Academy of Military Medical Sciences, Beijing, China.
authors: Jing
authors: J
authors: Yuan
authors: Institute of Microbiology and Biotechnology, University of Ulm, Ulm, Germany.
authors: Christian U
authors: CU
authors: Riedel
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001644:Bifidobacterium / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D013437:Carbon-Sulfur Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006714:Homoserine / Q000031:analogs & derivatives* / Q000378:metabolism; D007783:Lactones / Q000378:metabolism*; D008969:Molecular Sequence Data; D053038:Quorum Sensing; D016415:Sequence Alignment; D015854:Up-Regulation
chemical_list: D001426:Bacterial Proteins; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D006714:Homoserine; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria