Beyond movement: the dynamic roles of Type IV pili in cyanobacterial life

Type IV pili are versatile prokaryotic cell appendages that are extremely widespread in the bacterial and archaeal domains of life. The structure, dynamics, and functions of type IV pili have been most intensively studied in several species of heterotrophic bacteria, but these appendages also appear universal in cyanobacteria. Cyanobacterial type IV pili have much in common with those found in other bacteria, but they also show some unique features that may be crucial for facilitating the photoautotrophic lifestyles of cyanobacteria. Here, we discuss what is known of the structure and dynamic organization of cyanobacterial type IV pili. We discuss the multiple roles of cyanobacterial type IV pili in motility and phototaxis, sensory signal transduction, DNA uptake, and the formation of cell aggregates and biofilms. We conclude with some ideas on the likely importance of cyanobacterial type IV pilus functions in the natural environment and for biotechnological applications.