SummaryTo avoid detrimental interactions with intestinal microbes, the human epithelium is covered with a protective mucus layer that traps host defence molecules. Microbial properties such as adhesion to mucus further result in a unique mucosal microbiota with a great potential to interact with the host. As mucosal microbes are difficult to study in vivo, we incorporated mucin‐covered microcosms in a dynamic in vitro gut model, the simulator of the human intestinal microbial ecosystem (SHIME). We assessed the importance of the mucosal environment in this M‐SHIME (mucosal‐SHIME) for the colonization of lactobacilli, a group for which the mucus binding domain was recently discovered. Whereas the two dominant resident Lactobacilli, Lactobacillus mucosae and Pediococcus acidilactici, were both present in the lumen, L. mucosae was strongly enriched in mucus. As a possible explanation, the gene encoding a mucus binding (mub) protein was detected by PCR in L. mucosae. Also the strongly adherent Lactobacillus rhamnosus GG (LGG) specifically colonized mucus upon inoculation. Short‐term assays confirmed the strong mucin‐binding of both L. mucosae and LGG compared with P. acidilactici. The mucosal environment also increased long‐term colonization of L. mucosae and enhanced its stability upon antibiotic treatment (tetracycline, amoxicillin and ciprofloxacin). Incorporating a mucosal environment thus allowed colonization of specific microbes such as L. mucosae and LGG, in correspondence with the in vivo situation. This may lead to more in vivo‐like microbial communities in such dynamic, long‐term in vitro simulations and allow the study of the unique mucosal microbiota in health and disease.

BackgroundRecent scientific developments have shed more light on the importance of the host-microbe interaction, particularly in the gut. However, the mechanistic study of the host-microbe interplay is complicated by the intrinsic limitations in reaching the different areas of the gastrointestinal tract (GIT) in vivo. In this paper, we present the technical validation of a new device - the Host-Microbiota Interaction (HMI) module - and the evidence that it can be used in combination with a gut dynamic simulator to evaluate the effect of a specific treatment at the level of the luminal microbial community and of the host surface colonization and signaling.ResultsThe HMI module recreates conditions that are physiologically relevant for the GIT: i) a mucosal area to which bacteria can adhere under relevant shear stress (3 dynes cm−2); ii) the bilateral transport of low molecular weight metabolites (4 to 150 kDa) with permeation coefficients ranging from 2.4 × 10−6 to 7.1 × 10−9 cm sec−1; and iii) microaerophilic conditions at the bottom of the growing biofilm (PmO2 = 2.5 × 10−4 cm sec−1). In a long-term study, the host’s cells in the HMI module were still viable after a 48-hour exposure to a complex microbial community. The dominant mucus-associated microbiota differed from the luminal one and its composition was influenced by the treatment with a dried product derived from yeast fermentation. The latter - with known anti-inflammatory properties - induced a decrease of pro-inflammatory IL-8 production between 24 and 48 h.ConclusionsThe study of the in vivo functionality of adhering bacterial communities in the human GIT and of the localized effect on the host is frequently hindered by the complexity of reaching particular areas of the GIT. The HMI module offers the possibility of co-culturing a gut representative microbial community with enterocyte-like cells up to 48 h and may therefore contribute to the mechanistic understanding of host-microbiome interactions.

Autophagy is a catabolic trafficking pathway for bulk destruction and turnover of long-lived proteins and organelles via regulated lysosomal degradation. In eukaryotic cells, autophagy occurs constitutively at low levels to perform housekeeping functions, such as the destruction of dysfunctional organelles. Up-regulation occurs in the presence of external stressors (e.g. starvation, hormonal imbalance and oxidative stress) and internal needs (e.g. removal of protein aggregates), suggesting that the process is an important survival mechanism. However, the occurrence of autophagic structures in dying cells of different organisms has led to the hypothesis that autophagy may also have a causative role in stress-induced cell death. The identification within the last decade of a full set of genes essential for autophagy in yeast, the discovery of human orthologues and the definition of signalling pathways regulating autophagy have accelerated our molecular understanding and interest in this fundamental process. A growing body of evidence indicates that autophagy is associated with heart disease, cancer and a number of neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases. Furthermore, it has been demonstrated that autophagy plays a role in embryogenesis, aging and immunity. Recently, it has been shown that autophagy can be intensified by specific drugs. The pharmacological modulation of the autophagic pathway represents a major challenge for clinicians to treat human disease.

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