Effects of biofilm production on horizontal gene transfer to Vibrio cholerae

Abstract

The waterborne bacterial pathogen Vibrio cholerae utilizes a cell-cell communication system called quorum sensing to coordinate group behavior in both a human host and in aquatic environments. Virulence genes like the cholera toxin, biofilm genes for sticky secreted attachment factors, and competence genes for DNA uptake are all regulated by this population density-dependent system. In a human host, both virulence and biofilm genes are repressed at high cell densities that occur late in infection, presumably to promote transmission upon exhausting the host’s resources. However, in the natural environment, regulation is more complex. Namely, at high cell densities, repression of biofilm production is coordinated with activation of competence genes that can promote horizontal gene transfer (HGT). Based on this model, it was proposed that accumulation of biofilm material on bacterial cells could hinder the uptake of extracellular DNA in aquatic settings. In support of this hypothesis, significant decreases were detected in DNA uptake by V. cholerae strains engineered to overproduce biofilm. However, reductions in DNA uptake were also observed in strains that produced no biofilms. These results suggest that proper timing of biofilm formation plays an important role in the capacity of V. cholerae to engage in HGT, one mechanism thought to allow this pathogen to rapidly evolve in changing environments.