Influence of core divisome proteins on cell division in Streptomyces venezuelae ATCC 10712

Abstract

The sporulating, filamentous soil bacterium Streptomyces venezuelae ATCC 10712 differentiates under submerged and surface growth conditions. In order to lay a solid foundation for the study of development-associated division for this organism, a congenic set of mutants was isolated, individually deleted for a gene encoding either a cytoplasmic (i.e. ftsZ) or core inner membrane (i.e. divIC, ftsL, ftsI, ftsQ, ftsW) component of the divisome. While ftsZ mutants are completely blocked for division, single mutants in the other core divisome genes resulted in partial, yet similar, blocks in sporulation septum formation. Double and triple mutants for core divisome membrane components displayed phenotypes that were similar to those of the single mutants, demonstrating that the phenotypes were not synergistic. Division in this organism is still partially functional without multiple core divisome proteins, suggesting that perhaps other unknown lineage-specific proteins perform redundant functions. In addition, by isolating an ftsZ2p mutant with an altered −10 region, the conserved developmentally controlled promoter was also shown to be required for sporulation-associated division. Finally, microscopic observation of FtsZ-YFP dynamics in the different mutant backgrounds led to the conclusion that the initial assembly of regular Z rings does not per se require the tested divisome membrane proteins, but the stability of Z rings is dependent on the divisome membrane components tested. The observation is consistent with the interpretation that Z ring instability likely results from and further contributes to the observed defects in sporulation septation in mutants lacking core divisome proteins.

Hyphal compartmentalization and sporulation in Streptomyces require the conserved cell division protein SepX

“…In agreement with Santos-Benoit and coworkers 22 , we did not observe any additional membranous structures in the cytoplasm, also referred to as cross-membranes, which have been proposed to contribute to the subcellular organization of Streptomyces 23,24 . Apart from FtsZ, which is essential to form both vegetative and sporulation septa 6,25,26 , SepX is the first identified protein specifically required for cross-wall formation.…”

“…The Streptomyces life cycle is characterized by two distinct FtsZ-dependent modes of cell division that lead to the separation of growing hyphal filaments into multigenomic compartments and to the formation and release of unigenomic spores. While some recent progress has been made towards the understanding of the components involved in sporulation-specific sporulation 6,8,11,12 , little has been known about the determinants for FtsZ-mediated cross-wall formation. Here we describe the previously unknown cell division protein SepX, which is crucial for cross-wall formation and sporulation in Streptomyces .…”

“…The Z-ring acts as a scaffold for the assembly of the cell division machinery (the divisome) and guides the synthesis of septal peptidoglycan 4,5 . Streptomyces encode several orthologues of the core divisome components from E. coli or B. subtilis, such as FtsK, FtsQ, FtsL, DivIC and the cell wall synthetic enzymes FtsI and FtsW 6,7 . Moreover, additional factors have been identified that associate with the divisome and/or contribute to the efficient assembly and stability of Z-rings.…”

“…These proteins include the actinobacterial-specific protein SsgB, which has been reported to mark future sporulation-septation sites 8 , SepF, which functions as a membrane anchor for FtsZ [9][10][11] , SepH, which stimulates FtsZ filament assembly 12 , the two dynamin-like proteins DynA and DynB, which stabilize FtsZ-rings during sporulation, and two SepF-like proteins of unknown function 11 . Previous genetic studies have shown that none of the conserved and species-specific cell division proteins are essential for growth and viability in Streptomyces 6,7 . While the deletion of core cell division genes, including ftsQ, ftsL, divIC, ftsW or ftsI, appears to largely affect sporulation septation 6,8,[11][12][13] , a Streptomyces ΔftsZ mutant is both unable to sporulate and to compartmentalize the vegetative mycelium, resulting in a single-celled, branched mycelial network.…”

Microbial Musings – February 2021

“…However, FtsZ is still essential for spore formation where the divisome must form. In the new study, Cantlay has looked more at the function of the FtsZ protein in this bacterium, which is amenable to live-cell imaging as it can differentiate under submerged conditions [ 20 ]. They show that removal of most of the other core proteins of the divisome only result in partially blocks in sporulation septum formation.…”