Signalling early developmental events in two highly diverged Streptomyces species.

We review three main aspects of extracellular signalling in the initiation of aerial mycelium formation in two phylogenetically distant streptomycetes, S. coelicolor A3(2) and S. griseus: (1) gamma -butyrolactones; (2) a complex cascade of mostly undefined signals; and (3) progress towards defining an integrating endpoint of all this signalling. Although apparent orthologues of many of the genes involved are found in both species, some of the connectivities are different. Moreover, some of the genes involved in signalling have diverged more rapidly than known housekeeping genes. We propose that that this may be an important aspect of speciation, and that the differences in gene interactions may reflect the diverse soil microecologies to which different streptomycetes are adapted.