A mechanism for FtsZ-independent proliferation in Streptomyces

The central player in bacterial cell division, FtsZ, is essential in almost all organisms in which it has been tested, with the most notable exception being Streptomyces. Streptomycetes differ from many bacteria in growing from the cell tip and undergoing branching, similar to filamentous fungi. Here we show that limited cell damage, either mechanical or enzymatic, leads to near complete destruction of mycelial microcolonies of a Streptomyces venezuelae ftsZ mutant. This result is consistent with a lack of ftsZ-dependent cross-walls and may be inconsistent with a recently proposed role for membrane structures in the proliferation of ftsZ mutants in other Streptomyces species. Rare surviving fragments of mycelium, usually around branches, appear to be the preferred sites of resealing. Restoration of growth in hyphal fragments of both wild-type and ftsZ mutant hyphae can occur at multiple sites, via branch-like outgrowths containing DivIVA protein at their tips. Thus, our results highlight branching as a means of FtsZ-independent cell proliferation.