High-frequency rugose exopolysaccharide production by Vibrio cholerae

Vibrio cholerae can shift to a "rugose" phenotype, thereby producing copious exopolysaccharide (EPS), which promotes its environmental survival and persistence. We report conditions that promote high-frequency rugose EPS production (HFRP), whereby cells switch at high frequency (up to 80%) to rugose EPS production. HFRP appeared to be more common in clinical strains, as HFRP was found in 6 of 19 clinical strains (32%) (including classical, El Tor, and non-O1 strains) but in only 1 of 16 environmental strains (6%). Differences were found between strains in rugose colony morphology, conditions promoting HFRP, the frequency of rugose-to-smooth (R-S) cell reversion, and biofilm formation. We propose that rugose EPS and HFRP provide an evolutionary and adaptive advantage to specific epidemic V. cholerae strains for increased persistence in the environment.