Figure 5.

Role of chitin-rich mucus in Ciona gut. (A–C) Chitin enhances gut epithelial barriers as revealed by DSS-induced colitis-like phenotype. (A) The smooth continuous layer seen in control stomach epithelium (arrow) appears as having furrow structures (B) in the stomach of DSS-treated animals (arrow). (C) The surface of the epithelium remains mostly smooth (arrow) when treatment with DSS occurs in presence of chitin microparticles. Alexa Fluor 488-Phalloidin, green; DAPI, blue. Asterisk, gut lumen; white dotted lines highlight the surface morphology of the epithelium, smooth or with furrows. (A–C) reprinted from (47). (D, E) Biofilm assays using bacterial isolates cultured from Ciona gut are performed in vitro, with or without hydrolyzed chitin. (D) Shewanella sp. biofilms grown for 2 days in the presence/absence of chitin are quantified by crystal violet (CV) staining; plate shown with dried or solubilized stain (in acetic acid). A more intense staining is observed in presence of chitin. (E) Quantification of the solubilized CV staining of biofilms, measured with a microplate reader at OD₅₆₀, of various bacterial isolates from the Ciona gut, with or without hydrolyzed chitin present. Shewanella sp. and Pseudoalteronomas sp. biofilm formation is influenced by chitin, whereas no effect was noted in two different Vibrio spp. isolates. Asterisks indicate statistical significance calculated using two-tailed t-tests (P<0.01). Scale bar: (A), 20 µm; (B), 40 µm; (C) 100 µm.