Repressors of Quorum-Sensing-Induced Aggregation in Vibrio Cholerae

Abstract

Vibrio cholerae is the pathogen responsible for the disease cholera. To cause disease, V. cholerae must have the ability to form surface-attached multicellular communities called biofilms. The formation of surface biofilms is regulated by quorum sensing (QS). QS is a process in which bacteria collectively regulate gene expression in response to the secretion, accumulation, and detection of signaling molecules called autoinducers. The low cell density QS-state promotes biofilm formation while the high cell density QS-state promotes biofilm dispersal. Previous work in the Bassler laboratory identified an aggregation program in V. cholerae that occurs in liquid in the high cell density QS-state and is independent of components known to be required for surface biofilm formation. In this previous work, members of the Bassler group identified genes that function as activators of aggregation. In this study, I identified putative repressors of aggregation by performing a transposon mutagenesis screen in a low cell density-locked QS-state V. cholerae strain, a genetic background in which cells are normally unable to aggregate. This screen was successful, and I discovered two genes that act as repressors of aggregation: fbp and clpX. I validated both fbp and clpX and eliminated some mechanisms by which these genes may be regulating aggregation, which included control of the levels of O1 antigen and modulation of the QS-state of the cells. These findings increase our understanding of mechanisms that V. cholerae uses to transition between the planktonic and community phases of its life cycle.