VpsT is a transcriptional regulator required for expression of vps biosynthesis genes and the development of rugose colonial morphology in Vibrio cholerae O1 El Tor

Abstract

Vibrio cholerae switches between smooth and rugose colonial variants. The rugose variant produces more vibrio polysaccharides (VPS(El Tor)) and forms well-developed biofilms. Both phenotypes depend on expression of vps biosynthesis genes. We identified a positive transcriptional regulator of vps gene expression, VpsT, which is homologous to response regulators of two-component regulatory systems. Disruption of vpsT in the rugose variant yields smooth colonies, prevents formation of mature biofilms, and decreases vps gene expression. The interaction between VpsT and VpsR, a previously identified positive regulator of vps genes, was also investigated.

FIG. 1.

VpsT is required for the rugose colonial morphology. Colonial morphology of the smooth and rugose variants and the indicated deletion mutants formed on LB plates after 2 days of incubation at 30°C is shown.

FIG. 2.

Biofilm formation of vpsT and vpsR mutants. (A) Biofilm biomass measured with crystal violet-staining assay. The figure shows the average and standard deviation of three independent measurements for each mutant and for the wild-type parents. (B) Confocal scanning laser microscopic images of biofilms formed on borosilicate cover glass chambers. Top panels, horizontal projections; bottom panels, vertical projections.

FIG. 3.

vps gene expression in logarithmic, planktonic, and biofilm growth states. (A) Expression of vpsA, vpsL, vpsT, and vpsR in logarithmically grown wild-type variants and mutants. (B) vpsL transcription in planktonic cells (stippled bars) and in biofilm cells (grey bars) in the indicated mutants. Error bars indicate the standard deviation. Note the different y axis scales in all panels.