Ciliate-Vibrio cholerae interactions within a microbial loop: An experimental study

Abstract

Interactions between Vibrio cholerae and 2 Mexican athalassohaline-lake bacteria assemblages were studied in laboratory microcosms with the presence or absence of protists. Pre-cultivated and harvested vibrios were added as the food for protists at a concentration of 107 cells ml-1. Total direct bacterial counts, colony forming units on a selective (thiosulphate-citrate-bile salts-sucrose) medium, and V. cholerae indirect fluorescent antibody (FA) direct counts were measured. Numbers of V. cholerae decreased faster in the microcosms inoculated with protists and, moreover, the proportion of non-culturable vibrio counts increased. Comparison between the ciliate feeding rates upon flourescently labelled V. cholerae, Salmonella typhi and Shigella sp. showed that the ciliates fed preferably upon vibrios. Calculated grazing rates of Cyclidium glaucoma related to non-culturable but FA-positive V. cholerae were correlated to observed decrease in V. cholerae numbers.