Roles for flagellar stators in biofilm formation by Pseudomonas aeruginosa.

While Pseudomonas aeruginosa has only a single flagellum, its genome encodes two flagellar stators, called MotAB and MotCD. Here we report that despite no apparent alterations in swimming motility, mutations in either the MotAB or the MotCD stator render the strains defective for biofilm formation in both static and flow cell systems. Our data suggest distinct roles for the stators in early biofilm formation, with both the MotAB and MotCD stators playing a role in initial polar attachment of the bacterial cell to the surface (reversible attachment) and the MotAB stator also participating in the downstream adherence event of irreversible attachment. We also show that the initial polar attachment of P. aeruginosa to two different abiotic surfaces occurs largely at the flagellated end of the cell, a finding that should help develop models for early attachment events. Interestingly, in flowing conditions, a mutation in either stator alone revealed a more severe biofilm defect than mutating both stators or mutating the flagellum. Our data suggest that defects in biofilm formation observed for the stator mutants may be in part due to impacting flagellar reversal rates.