Role of Functional Amyloids in Morphogenesis

Within the bacterial domain streptomycetes have an unusual life cycle. These microorganisms colonize dead and living organic material by means of hyphae that grow at their apices. The hyphae are part of an interconnected network, which is called a mycelium. 

At a certain moment, hyphae grow out of the substrate into the air. The aerial hyphae eventually septate to form chains of exospores that, after dispersal, give rise to new mycelia. Streptomycetes not only grow in moist substrates or in the air but they may also grow over and attach to hydrophobic surfaces such as the leaf of a plant or the skin of an animal. 

The Claessen lab is interested in the mechanisms enabling streptomycetes to leave the aqueous environment and to grow into the air or to attach to a hydrophobic solid. Two classes of proteins, called chaplins and rodlins, were identified that are involved in these processes. Strikingly, chaplins function by assembling into small amyloid-like fibrils at the hyphal surface. Amyloids are filamentous protein structures ±10 nm wide and 0.1–10 μm long that share a structural motif, the cross-β structure. These fibrils are usually associated with degenerative diseases in mammals (like Alzheimer’s). This work has demonstrated that amyloids can also be beneficial to some microbes enabling them to mechanically invade abiotic and biotic substrates.

© Dennis Claessen 2017