Structural proteins involved in emergence of microbial aerial hyphae

Filamentous fungi and filamentous bacteria (i.e., the streptomycetes) belong to different kingdoms that diverged early in evolution. Yet, they adopted similar lifestyles. After a submerged feeding mycelium has been established, hyphae grow into the air and form aerial structures from which (a)sexual spores can develop. These spores are dispersed and can give rise to a new mycelium. Some of the key processes involved in the formation of aerial hyphae by these microbes appear to be very similar. In both cases molecules that lower the surface tension are secreted into the aqueous environment, thereby enabling hyphae to grow into the air. Aerial hyphae are then covered with a hydrophobic film. In fungi, this film is characterized by a mosaic of parallel rodlets, while similar rodlets have also been observed on aerial structures of filamentous bacteria. Although the erection of aerial hyphae in both filamentous fungi and filamentous bacteria is dependent upon (poly)peptides that are structurally unrelated, they can, at least partially, functionally substitute for each other.