A mechanism for FtsZ-independent proliferation in Streptomyces

Abstract

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.

ylmD and ylmE genes are dispensable for growth, cross-wall formation and sporulation in Streptomyces venezuelae

“…Most of the conserved cell division genes of this cluster have been inactivated in Streptomyces without the anticipated lethality, based on studies of many other bacteria. Actually, the full essentiality of ftsZ reported in most bacteria is not observed in Streptomyces ( McCormick et al, 1994 ; Santos-Beneit et al, 2017 ). Despite the importance of this cluster, there are still some genes of the Streptomyces dcw cluster that remain unstudied, the most notable example are the two conserved genes ( ylmDE ) immediately adjacent to ftsZ .…”

“…However, Streptomyces constitutes an exception to this event. Both Streptomyces coelicolor and S. venezuelae ftsZ -null mutants are able to grow and to form aerial mycelium; although are unable to convert aerial hyphal filaments into spores ( McCormick et al, 1994 ; Santos-Beneit et al, 2017 ). The Streptomyces ftsZ gene forms part of the well-conserved prokaryotic division and cell wall ( dcw ) gene cluster that includes genes required for efficient growth ( divIVA ), cell wall biosynthesis ( mur genes) and cell division ( ftsZ, ftsQ , ftsW , ftsI , fstL ).…”

A conserved cell division protein directly regulates FtsZ dynamics in filamentous and unicellular actinobacteria

“…Sporulation septa eventually constrict, leading to cell-cell separation and the release of unigenomic spores. Both these forms of cell division require FtsZ, but unlike in most other bacteria the ftsZ gene can be deleted in Streptomyces , leading to viable hyphae that lack both cross-walls and sporulation septa (McCormick et al, 1994; Santos-Beneit et al, 2017). The Streptomyces divisome is comprised of several conserved core divisome components including FtsQ, DivIC, FtsL, FtsEX, and the cell wall synthesis proteins FtsI and FtsW (McCormick, 2009).…”

Turgor Pressure and Possible Constriction Mechanisms in Bacterial Division

“…A possible example is in Gram-positive Streptomyces species that grow as vegetative hyphae, where the PM can invaginate and form membrane cross walls without Z ring or CW support ( Celler et al, 2016 ). This suggests that membrane production may be sufficient for membrane invagination against turgor pressure [However, the existence of cross walls in Streptomyces lacking FtsZ has been questioned by a recent study ( Santos-Beneit et al, 2017 )]. Membrane septa without CW were also observed in B. subtilis when one peptidoglycan synthase, PBP2B, was deleted ( Daniel et al, 2000 ).…”