Molecular Biotechnology, Institute of Biology, Universiteit Leiden, The Netherlands, will give a talk:
"New insights into the control of cell division and DNA segregation in Streptomyces by high resolution imaging"
Th, 21 December 2017, 10:0 a.m.,
Lecture Hall 2, UZA I
Join us for an exciting talk!
ABSTRACT:
Streptomycetes are model organisms for bacterial development. These mycelial microorganisms undergo a complex multicellular life cycle, and propagate via sporulation. The cell division machinery of streptomycetes is very similar to that of bacteria that divide via binary fission, whereby the cell division scaffold is formed by FtsZ. However, the systems that control the onset and localization of FtsZ-ring formation division are different. This reflects the difference between the demands of planktonic versus mycelial growth. Our research focuses on understanding the regulatory mechanisms that control cell division in time and space in the multinucleoid Streptomyces hyphae.
Cell division in vegetative hyphae is unique in several ways. Firstly, the hyphae can grow without FtsZ, making these bacteria the only known organisms in which cell division is dispensable for growth 1. Most of the canonical divisome components are apparently irrelevant at this stage, and the septa are placed in a rather haphazard way, without clear logic. Eventually, the cross-walls separate the hyphae into multinucleoid compartments. A major challenge lies in preventing nucleoid damage during septum placement. Using innovative high resolution EM techniques such as cryo-electron tomography and correlative light and electron microscopy we discovered dedicated membrane assemblies that create nucleoid-free zones in the vegetative hyphae 2,3. These so-called cross-membranes likely keep the DNA away from sites of peptidoglycan synthesis during apical growth and cell division.
Sporulation-specific cell division, which requires the divisome, sets entirely different demands. The aerial hyphae differentiate into chains of unigenomic spore. Here, the challenge lies in ensuring symmetry and coordination of septum spacing. Sporulation-specific cell division in streptomycetes is positively controlled, whereby FtsZ is recruited to the septum sites by the divisome protein SsgB in an SsgA-dependent manner 4. SsgB is a member of the family of SsgA-like proteins that occur exclusively in morphologically complex actinomycetes and control processes related to peptidoglycan (PG) synthesis and remodelling. We recently identified another piece of the jigsaw, showing that docking of SsgB to the membrane requires SepG (previously called YlmG) 5. The few spores seen in sepG null mutants are deformed, whereby the nucleoid is localized at the periphery of the spores rather than condensed in the centre. We are now beginning to understand some of the key regulatory processes that govern the two mechanistically different cell division processes in Streptomyces. The nucleoid in combination with Streptomyces-specific proteins and macromolecular complexes thereby play a key role in controlling cell division in time and space. Our most recent data and a summarising model will be presented.
References
1 McCormick, J. R., Su, E. P., Driks, A. & Losick, R. Growth and viability of Streptomyces coelicolor mutant for the cell division gene ftsZ. Mol Microbiol 14, 243-254 (1994).
