Abstract
There are numerous bacteria reside within the mammalian gastrointestinal tract. Among the intestinal bacteria, Akkermansia, Bacteroides, Bifidobacterium, and Ruminococcus closely interact with the intestinal mucus layer and are, therefore, known as mucosal bacteria. Mucosal bacteria use host or dietary glycans for colonization via adhesion, allowing access to the carbon source that the host’s nutrients provide. Cell wall or membrane proteins, polysaccharides, and extracellular vesicles facilitate these mucosal bacteria-host interactions. Recent studies revealed that the physiological properties of Bacteroides and Bifidobacterium significantly change in the presence of co-existing symbiotic bacteria or markedly differ with the spatial distribution in the mucosal niche. These recently discovered strategic colonization processes are important for understanding the survival of bacteria in the gut. In this review, first, we introduce the experimental models used to study host-bacteria interactions, and then, we highlight the latest discoveries on the colonization properties of mucosal bacteria, focusing on the roles of the cell surface architecture regarding Bacteroides and Bifidobacterium.
Highlights
A diversity of microorganisms co-exists with humans; the estimated total number of bacteria in the human body is approximately 3.8 × 1013 (Sender et al, 2016a,b)
Several studies indicated that the outer mucus layer is enriched in mucindegrading/consuming bacteria, such as Akkermansia muciniphila, Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides vulgatus, Ruminococcus gnavus, Ruminococcus torques, and Bifidobacterium bifidum
The pilus protein from Lactobacillus rhamnosus GG (Nishiyama et al, 2016b), a sialidase from B. bifidum ATCC15696 (Nishiyama et al, 2017), and the sialic acid-binding carbohydratebinding module (CBM40) conserved in trans-sialidase (RgNanH) from R. gnavus ATCC29149 (Owen et al, 2017) were all characterized as factors that could adhere to intestinal mucins
Summary
A diversity of microorganisms co-exists with humans; the estimated total number of bacteria in the human body (for a reference weight of 70 kg) is approximately 3.8 × 1013 (Sender et al, 2016a,b). Adhesion can be quantified using crystal violet staining (Collins et al, 2012) or fluorescent dye staining (Mackenzie et al, 2010; Etzold et al, 2014) Using this experimental approach, B. fragilis, capable of adhering to the murine mucus layer in vivo, adhered well to both murine and porcine colonic mucin-immobilized microtiter plates (Huang et al, 2011). B. fragilis, capable of adhering to the murine mucus layer in vivo, adhered well to both murine and porcine colonic mucin-immobilized microtiter plates (Huang et al, 2011) These data suggest that the adhesion phenotype determined using this in vitro experimental approach can be translated to the in vivo context. This experimental approach was used to screen bacteria with the ability to adhere to mucin sulfo- and sialyl-sugar chains using mucin pre-treated with sialidase and sulfatase (Huang et al, 2013; Nishiyama et al, 2014)
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