Under favorable growth conditions, a typical Streptomyces spore starts to germinate by extruding one or two germ tubes (Figure 1). These tubes
elongate by tip extension and grow into a branched hyphal network known as the vegetative mycelium. Polar growth and hyphal branching is
directed by the essential protein DivIVA. This coiled-coil protein is part of a large cytoplasmic complex called the polarisome, which is crucial for
the insertion of new cell envelope material at the extending tip 4-7. During vegetative growth, the hyphal filaments become compartmentalized
by the infrequent formation of so-called cross-walls 8. The formation of these cross-walls requires FtsZ, the tubulin-like cytoskeletal protein that
is essential for cell division in most bacteria 9. In Streptomyces, however, these vegetative cross-walls do not lead to constriction and cell-cell
separation and therefore the mycelial mass remains as a network of inter-connected syncytial compartments. In response to nutrient limitation
and other signals that are not well understood, specialized aerial hyphae break away from the vegetative mycelium and grow into the air 3. The
erection of these structures initiates the reproductive phase of development, during which the long multi-genomic aerial hyphae become divided
into dozens of equally sized unigenomic prespore compartments. This massive cell division event is driven by the synchronous constriction
of multiple FtsZ rings within single sporogenic hyphae 2,10. Morphological differentiation is completed by the release of dormant, thick-walled