Vibrio cholerae monolayer formation reveals a key role for 5 ∆ Ψ in the transition to permanent attachment 6 7

1 A bacterial monolayer biofilm is a collection of cells attached to a surface but not to 2 each other. Monolayer formation is initiated when a bacterial cell forms a transient 3 attachment to a surface. While some transient attachments are broken, others 4 transition into the permanent attachments that define the monolayer biofilm. In this 5 work, we describe the results of a large-scale, microscopy-based genetic screen for 6 Vibrio cholerae mutants that are defective in formation of the monolayer biofilm. This 7 screen identified mutations that alter both transient and permanent attachment. 8 Transient attachment was somewhat slower in the absence of flagellar motility. 9 However, flagellar mutants eventually formed a robust monolayer. In contrast, in the 10 absence of the flagellar motor, monolayer formation was severely impaired. A number 11 of proteins that modulate the V. cholerae ion motive force were also found to affect the 12 transition from transient to permanent attachment. Using chemicals that dissipate 13 various components of the ion motive force, we discovered that dissipation of the 14 membrane potential ∆Ψ completely blocks the transition from transient to permanent 15 attachment. We propose that, as a bacterium approaches a surface, the interaction of 16 the flagellum with the surface leads to a transient hyperpolarization of the bacterial cell 17 membrane. This, in turn, initiates the transition to permanent attachment.