Positive control of cell division : FtsZ is recruited by SsgB during sporulation of Streptomyces
mardi 18 octobre 2011 - 11:30-12:30
Gilles P. van Wezel
Gilles P. van Wezel Molecular Biotechnology, Leiden University, Leiden, Netherlands.
Lieu : Salle de conférence, bâtiment 400.
In bacteria that divide by binary fission, cell division starts with the polymerization of the tubulin homologue FtsZ at mid-cell to form a cell division scaffold (the Z-ring), followed by recruitment of the other divisome components. Streptomycetes are filamentous soil bacteria with a complex life cycle, which have a mycelial life style and propagate via sporulation. In these organisms two types of cell division occur ; during normal growth cross-walls are formed that compartmentalise the hyphae but do not lead to physical separation, while during sporulation ladders of up to 100 Z-rings are formed in the aerial hyphae, producing uninucleoid spores. Sporulation-specific cell division requires an unparallelled complex coordination of septum-site localization, peptidoglycan synthesis and DNA segregation. We discovered that the SsgA-like proteins (SALPs), which are only found in sporulating actinomycetes, help orchestrate developmental cell division in streptomycetes . The textbook view of bacterial cell division control starts from the principle of negative check points, among others involving MinCDE and Noc, that prevent incorrect Z-ring positioning . We recently demonstrated positive control of septum-site localization during sporulation of Streptomyces, via the direct recruitment of FtsZ by the membrane-associated divisome component SsgB . In turn, SsgB is controlled by the orthologous cell division activator SsgA. In vitro studies demonstrated that SsgB acts similarly to ZipA and promotes the polymerization of FtsZ. The interactions between the various cell division proteins were studied in vivo by time-lapse imaging and FRET-FLIM and corroborated via two-hybrid studies. When cell division is initiated, the turn-over of FtsZ protofilaments increases strongly, similar to tubulin turn-over during eukaryotic mitosis. The surprising positive control of Z-ring formation by SsgB implies the evolution of an entirely new way of Z-ring control, which may be explained by the absence of a mid-cell reference point in the long multi-nucleoid hyphae. A model of our current understanding of sporulation-specific cell division in Streptomyces is presented.
Contact : g.wezel (AT) chem.leidenuniv.nl ; Tel : +31 715274310