Effect of various biophysicochemical conditions on toxigenicity of Vibrio cholerae 01 during survival with a green alga, Rhizoclonium fontanum, in an artificial aquatic environment.

Toxigenic and nontoxigenic strains of Vibrio cholerae 01 occur in the natural aquatic environment. It is not clear whether V. cholerae 01 lose toxigenicity and become nontoxigenic during survival in the aquatic environment as a result of the effect of various biophysicochemical conditions (e.g., sunlight, pH, temperature, competition with other bacteria for nutrients, etc.). Five toxigenic strains were exposed to artificial aquatic environments in the presence of a filamentous green alga. Rhizoclonium fontanum, and recovered after different time intervals (0 and 0.5 h, 3, 6, 9, and 15 days). This experimental system was exposed to sunlight and the V. cholerae 01 were in competition for nutrients with resident bacterial flora from R. fontanum. The toxigenicity of Vibrio cholerae 01 that were recovered at different time intervals was assessed by tissue culture assay using Vero cells. The toxigenicity of recovered strains was compared with that of the parent strains. The results demonstrated that toxigenic V. cholerae 01 are unlikely to lose their toxigenicity in aquatic environments as a result of the effects of various biophysicochemical conditions. These results are consistent with the hypothesis of environmental reservoirs of V. cholerae.