The Cyanobacterial Pilus Assembly Complex: Roles in Biofilm Regulation and Protein Secretion

Speaker: Rakefet Schwarz (Bar-Ilan University)

Host: Karl Forchhammer (CMFI)

Date & Time: 21.05.2026 | 12:30 – 2 p.m.

Venue:  E Building, 9A23

Public Event. No registration needed and everyone welcome. 

Abstract: 

Bacterial type IV pili (T4P) are multifunctional structures involved in motility, adhesion, DNA uptake, and pathogenicity. In heterotrophic bacteria, T4P are typically required for biofilm formation. In contrast, in the model cyanobacterium Synechococcus elongatus PCC 7942, inactivation of the T4P assembly complex promotes robust biofilm formation in an otherwise planktonic organism. Our findings indicate that the T4P complex mediates the secretion of a biofilm inhibitor that represses transcription of genes encoding extracellular matrix components and their associated secretion machinery, thereby maintaining a planktonic lifestyle. Notably, the cyanobacterial T4P complex includes unique components in addition to those conserved in heterotrophic bacteria: A homolog of the RNA chaperone Hfq and a previously uncharacterized protein that we term EbsA (essential for biofilm suppression protein A). Disruption of these components, as well as conserved T4P components shared with heterotrophic bacteria, abolishes T4P assembly, DNA competence, and the biofilm self-suppression mechanism. Recent data suggest that the cyanobacterial T4P complex facilitates signal peptide-dependent secretion of non-pilus proteins. In this seminar, I will discuss these findings, potential mechanisms underlying T4P-dependent secretion and the functional advantages of coupling pilus assembly with protein secretion within a single molecular complex.