High-frequency rugose exopolysaccharide production by Vibrio cholerae

Abstract

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.

FIG. 1.

Colony morphology of smooth and rugose variants of V. cholerae. (A) Colonies at 24 h. (B) Colonies at 72 h.

FIG. 2.

The rugose variant of V. cholerae classical biotype (sixth pandemic) strain NCTC 6585 produces an extracellular glycocalyx. TEM of ruthenium red-stained thin sections of smooth and rugose cells of classical strain NCTC 6585. Micrographs show no stained matrix between smooth cells (left panel) and densely stained matrix between rugose cells (arrow, right panel).

FIG. 3.

Biofilm formation by smooth and rugose colony variants of V. cholerae. Glass test tubes containing 500 μl of LB broth were inoculated with a 1:100 dilution of overnight cultures of N16961, NCTC 6585, and Aldova O37 strains and incubated statically at room temperature for 24 h. Quantitative biofilm assays were performed as described previously (24).