Abstract
Cell division during the reproductive phase of the Streptomyces life-cycle requires tight coordination between synchronous formation of multiple septa and DNA segregation. One remarkable difference with most other bacterial systems is that cell division in Streptomyces is positively controlled by the recruitment of FtsZ by SsgB. Here we show that deletion of ylmD (SCO2081) or ylmE (SCO2080), which lie in operon with ftsZ in the dcw cluster of actinomycetes, has major consequences for sporulation-specific cell division in Streptomyces coelicolor. Electron and fluorescence microscopy demonstrated that ylmE mutants have a highly aberrant phenotype with defective septum synthesis, and produce very few spores with low viability and high heat sensitivity. FtsZ-ring formation was also highly disturbed in ylmE mutants. Deletion of ylmD had a far less severe effect on sporulation. Interestingly, the additional deletion of ylmD restored sporulation to the ylmE null mutant. YlmD and YlmE are not part of the divisome, but instead localize diffusely in aerial hyphae, with differential intensity throughout the sporogenic part of the hyphae. Taken together, our work reveals a function for YlmD and YlmE in the control of sporulation-specific cell division in S. coelicolor, whereby the presence of YlmD alone results in major developmental defects.
Highlights
In unicellular bacteria, cell division divides a mother cell in two identical daughter cells, each containing a single copy of the chromosome
Using cryo-electron tomography, our lab and others showed that intracellular membrane assemblies or cross-membranes are involved in DNA protection during septum synthesis in young vegetative hyphae, suggesting a novel way of cell-division control[17,18]
Canonical division resulting in cell fission occurs during sporulation-specific cell division, which requires all components of the divisome[16,21]
Summary
While the majority of the spores of the complemented ylmD mutant had a regular appearance, those of the complemented ylmE mutants still showed variable lengths (Fig. 2B) This partial complementation suggests that the deletion of ylmE may have polar effect on the expression of its downstream genes. Given the impact of ylmDE on sporulation, we analyzed how YlmD and YlmE were localized in the hyphae of S. coelicolor To this end, constructs based on the low-copy number vector pHJL401 were prepared to allow the expression of YlmD-eGFP and YlmE-eGFP fusion proteins, which were expressed from the natural ftsZ promoter region (see Materials and Methods section for details). YlmD-eGFP and YlmE-eGFP signals decreased to the level as in vegetative growth These results suggest YlmD and YlmE proteins are active primarily during the phase of sporulation-specific cell division. We are performing detailed structural and functional analysis of YlmD and YlmE, to elucidate their biochemical function and their precise role in bacterial cell division
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