Adhesins acquired in the aquatic environment and Vibrio cholerae colonization of intestinal cells

Recent results for Vibrio cholerae interactions with bivalves and chitin-containing substrates are reviewed. Chitin, composed of -1,4-linked N-acetylglucosamine residues, is one of the most abundant biopolymers in nature and the most abundant in the marine environment. V. cholerae connection to chitin is a well known phenomenon and one of the best documented examples of a successful bacteria-substrate interaction, affecting both the lifestyle of the microorganisms and natural system functioning. In sea water, vibrios can be entrapped by filter-feeding invertebrates that sieve suspended food particles from the aquatic environment. Persistence of bacteria in bivalves depends on different factors including their sensitivity to the bactericidal activity of hemolymph. Both V. cholerae survival inside bivalves and chitin colonization depend on cell surface properties, with contribution of different ligands (e.g. chitin-binding proteins, MSHA). The role of these ligands in interactions with human surfaces is discussed and evidence is presented supporting (i) the link between vibrio persistence in the environment (both inside bivalves and adhering to chitin-containing surfaces) and infection of the human host, and (ii) the hypothesis that virulence mechanisms of bacteria that have environmental reservoirs represent a consequence of adaptive mechanisms to the environment.