Mucin utilisation and host interactions of the novel intestinal microbe Akkermansia muciniphila

Keywords .Mucin, A. muciniphila , mucin degradation, molecular techniques, host responseMucins are the major organic components of the defence barrier, known as mucus, covering epithelial cells in many organs, including the entire gastrointestinal (GI) tract. Microbes that can associate with mucins benefit from this interaction since they can access nutrients. Mucin-degrading bacteria are therefore an important community that have not been extensively studied as the substrate itself, mucin, is a complex and high molecular weight glycoprotein.The work presented here is focused on the identification and isolation of mucin-degrading bacteria from the GI tract, their degradation of mucin and their interaction with the host.Mucin-degrading bacteria were analysed by combining molecular- and cultivation-based approaches. The faecal mucin-degrading bacterial community was found to be highly diverse and host-specific. A novel isolate, representing a novel genus, was cultured from the highest dilution of the enrichment of a single individual. This intestinal isolate, Akkermansia muciniphila, was found to grow to a limited extent on a very limited amount of substrates but grew efficiently on mucin. Phylogenetic analysis based on 16S rRNA sequences indicated that A. muciniphila belonged to the phylum Verrucomicrobia, which was not known to contain intestinal members. Moreover, 16S rRNA genes from A. muciniphila have been retrieved in several clone libraries derived from either faecal or biopsy samples from human and mice. In addition, A. muciniphila was found to be rather abundant in the GI tract. Based on fluorescent in situ hybridisation and quantitative PCR, A. muciniphila was found to represent an average of 10 ⁹ cells / g faecal sample. A negative correlation between the concentration of faecal mucin and the number of A. muciniphila was observed, suggesting it to be involved in mucin degradation in vivo . Several specific enzymes, mostly glycosidases were found to be secreted during its growth on mucin that was degraded for a major part (85%). Hence, the specific impact of A. muciniphila on the host was investigated in germ-free mice and compared to that of the non mucin-degrading bacterium L. plantarum . Transcriptomic microarray analysis showed that both A. muciniphila and L. plantarum modulated a similar number of genes but that host response was found to be highly specific for each bacterium, depending on the anatomical location. Amongst the major responses, we could detect for A. muciniphila a regulation of the immune response, cell proliferation, cell adhesion and apoptosis, and for L. plantarum a regulation of the lipid metabolism.Overall, this work has brought new insights into the mucin-degrading community of bacteria, and in particular the role of A. muciniphila,an abundant human mucin-degrading bacterium.