The type IV pilin PilA couples surface attachment and cell cycle initiation in Caulobacter crescentus

Understanding how bacteria colonize surfaces and regulate cell cycle progression in response to cellular adhesion is of fundamental importance. Here, we used transposon sequencing in conjunction with FRET microscopy to uncover the molecular mechanism how surface sensing drives cell cycle initiation in Caulobacter crescentus . We identified the type IV pilin protein PilA as the primary signaling input that couples surface contact to cell cycle initiation via the second messenger c-di-GMP. Upon retraction of pili filaments, the monomeric pilin reservoir in the inner membrane is sensed by the 17 amino-acid transmembrane helix of PilA to activate the PleC-PleD two component signaling system, increase cellular c-di-GMP levels and signal the onset of the cell cycle. We termed the PilA signaling sequence CIP for cell cycle initiating pilin peptide. Addition of the chemically synthesized CIP peptide initiates cell cycle progression and simultaneously inhibits surface attachment. The broad conservation of the type IV pili and their importance in pathogens for host colonization suggests that CIP peptide mimetics offer new strategies to inhibit surface-sensing, prevent biofilm formation and control persistent infections. Significance Statement Pili are hair-like appendages found on the surface of many bacteria to promote adhesion. Here, we provide systems-level findings on a molecular signal transduction pathway that interlinks surface sensing with cell cycle initiation. We propose that surface attachment induces depolymerization of pili filaments. The concomitant increase in pilin sub-units within the inner membrane function as a stimulus to activate the second messenger c-di-GMP and trigger cell cycle initiation. Further-more, we show that the provision of a 17 amino acid synthetic peptide corresponding to the membrane portion of the pilin sub-unit mimics surface sensing, activates cell cycle initiation and inhibits surface attachment. Thus, synthetic peptide mimetics of pilin may represent new chemotypes to control biofilm formation and treat bacterial infections.