Functional Amyloid Confer Defense Against Predatory Bacteria

bacteriovorus is a predatory bacterium that preys on Gram-negative bacteria. B. bacteriovorus invades the prey-cell periplasm – the space between the inner and outer membrane – leaches host nutrients to replicate, and ultimately lyses the infected cell to exit and find new prey. The infectious life cycle of B. bacteriovorus is, in many ways, comparable to a bacteriophage. However, unlike phage resistance, defense against B. bacteriovorus has not been widely investigated and until recently, was not thought to exist. At this conference I will present my work uncovering a “molecular suit of armor” which blocks infection before it can occur. Curli fibers are polymers of the functional amyloid protein CsgA formed on the outer membrane of many bacteria. Using genetic and microscopy-based assays, we suggest that curli fibers form a barrier that shields susceptible cells. Bioinformatic analysis of bacterial amyloid proteins demonstrates previously unappreciated diversity in amyloid encoding genes and that production of these fibers is selectively enriched in bacteria with two membranes, the obligatory targets of B. bacteriovorus. In support of these findings, functional amyloid proteins from Pseudomonas aeruginosa [AW1] also blocked B. bacteriovorus infection. These observations suggest an unappreciated role for curli-like fibers. Indeed, we found that amyloid barriers block not only B. bacteriovorus but limit infection by other predatory bacteria too. In total, this work establishes that functional amyloids, and extracellualr barriers, are an important new dimension for the bacterial immune system.