Genetic Analysis of Vibrio cholerae Monolayer Formation Reveals a Key Role for ΔΨ in the Transition to Permanent Attachment

A bacterial monolayer biofilm is a collection of cells attached to a surface but not to each other. Monolayer formation is initiated when a bacterial cell forms a transient attachment to a surface. While some transient attachments are broken, others transition into the permanent attachments that define a monolayer biofilm. In this work, we describe the results of a large-scale, microscopy-based genetic screen for Vibrio cholerae mutants that are defective in formation of a monolayer biofilm. This screen identified mutations that alter both transient and permanent attachment. Transient attachment was somewhat slower in the absence of flagellar motility. However, flagellar mutants eventually formed a robust monolayer. In contrast, in the absence of the flagellar motor, monolayer formation was severely impaired. A number of proteins that modulate the V. cholerae ion motive force were also found to affect the transition from transient to permanent attachment. Using chemicals that dissipate various components of the ion motive force, we discovered that dissipation of the membrane potential (Delta Psi) completely blocks the transition from transient to permanent attachment. We propose that as a bacterium approaches a surface, the interaction of the flagellum with the surface leads to transient hyperpolarization of the bacterial cell membrane. This, in turn, initiates the transition to permanent attachment.