Disease to Dirt: The Biology of Microbial Amyloids

Amyloid fibers are β-sheet-rich protein polymers that are highly resistant to denaturation. The distinguishing amyloid fold can be adopted by a variety of proteins, without a shared primary structure, and is found in nearly all cell types. Despite the fact that amyloids have a richly informed scientific history, the diverse biology contributed by amyloids is only beginning to be appreciated. Initial amyloid studies focused on the intimate association of amyloid formation with cytotoxicity and neurodegenerative diseases like Alzheimer's, Huntington's, and the prion encephalopathies. Despite amyloid's somewhat sinister past, recent work on “functional” amyloids has revealed numerous ways that amyloids contribute to normal cellular biology [1]. Included among the activities in which amyloids participate are melanin production, the ability to act as non-Mendelian inheritable genetic elements, and as extracellular molecular scaffolds that hold bacterial communities together. The amyloid fold is tailor-made for the extracellular space, as amyloid polymers can self-assemble without requiring exogenous energy and the polymers are resistant to a slew of harsh denaturants that would devastate most protein folds. This article will address questions involving the various roles of bacterial amyloids in host, polymicrobial, and environmental interactions.