Investigating the molecular mechanisms of the interactions between Lactobacillus reuteri strains and intestinal mucus
Mucus is the first point of contact between the gut microbiota and the host. Here we used the gut symbiont Lactobacillus reuteri to investigate the molecular mechanisms underlying the interactions between gut bacteria and mucus. Firstly, the mucus binding ability of a collection of L. reuteri strains from different vertebrate hosts was assessed in vitro against mucus extracted from mouse and porcine gastrointestinal tracts. The adhesion profile was strain-specific showing the highest binding phenotype for strain ATCC 53608 (a pig isolate) and binding ability for a number of L. reuteri human isolates. Genome sequencing of the ATCC 53608 strain and comparative genomics was carried out to gain novel insights in the strain-specific determinants of L. reuteri adhesion to mucus. The second part of this work investigated the occurrence at the genetic and protein level of two specific cell surface proteins, MUB and Lar_0958, expressed by the ATCC 53608 strain and human strains, respectively and their role in mediating mucus binding and autoaggregation ability of L. reuteri strains, as determined by flow-cytometry and in vitro mucus binding assays with recombinant and native proteins. Finally a quantitative proteomic approach, stable isotope labelling with amino acids in cell culture (SILAC), was used to identify novel mucus binding protein candidates. This was achieved through detection of increased cell surface protein expression when L. reuteri was grown in presence of mucins, resulting in induced mucus binding phenotype. Collectively, these results shed new light on the nature and distribution of strain-specific surface proteins mediating L. reuteri adhesion to mucus.
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