Sugars inhibit expression of the rugose phenotype of Vibrio cholerae

Abstract

Vibrio cholerae can shift to a rugose colony phenotype, reflecting expression of an exopolysaccharide that provides protection against a variety of environmental stresses. Our data indicate that expression of the rugose phenotype is inhibited by a variety of sugars, including sucrose, dextrose, arabinose, fructose, and maltose. Inhibition by sucrose may be one factor in explaining the failure of rugose strains to grow on thiosulfate citrate bile salts sucrose agar, the primary selective medium for V. cholerae.

FIG. 1.

Effects of various carbon sources on expression of the rugose phenotype of V. cholerae. Tests were performed by plating an appropriately diluted rugose culture on L agar supplemented with the concentrations (wt/vol) of sugars shown. The plates were incubated (1 day at 37°C, followed by 7 days at room temperature), and the results were observed at 18- to 20-h intervals. The data indicate the maximum incubation time (in hours) required to convert all smooth colonies to the rugose phenotype.

FIG. 2.

Colony phenotypes of a rugose variant of V. cholerae strain N16961 on various agar plates. A, standard L agar plate; B, TCBS agar plate; C, standard L agar plate supplemented with TCBS agar ingredients without the sucrose component; D, TCBS agar without sucrose. Note that rugose cells were partially formed at 48 h of incubation in the center of the colonies in rows C and D.