Berlin 2015 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 36: Cell adhesion, mechanics and migration II
BP 36.5: Vortrag
Mittwoch, 18. März 2015, 16:00–16:15, H 1058
Bistable forespore engulfment in B. subtilis by a zipper mechanism in absence of the cell wall — •Nikola Ojkic1, Javier López Garrido2, Kit Pogliano2, and Robert G. Endres1 — 1Department of Life Sciences, Imperial College, London, United Kingdom — 2Division of Biological Sciences, University of California, San Diego, La Jolla, California, USA
To survive starvation, the bacterium Bacillus subtilis forms durable spores. The initial step of sporulation is asymmetric cell division, leading to a large mother-cell and a small forespore compartment. After division is completed, the mother cell engulfs the forespore in a slow process based on cell-wall degradation and synthesis. However, recently a new cell-wall independent mechanism was shown to significantly contribute, which can even lead to fast engulfment in ∼ 60 % of the cases when the cell wall is removed. In this backup mechanism, strong ligand-receptor binding between mother-cell protein SpoIIIAH and forespore-protein SpoIIQ leads to zipper-like engulfment, but quantitative understanding is missing. We combined florescence image analysis and stochastic Langevin simulations of the fluctuating membrane to investigate the origin of fast bistable engulfment in absence of the cell wall. We predict regions of osmotic pressure and membrane-surface tension that produce successful engulfment. Our cell morphologies compare favorably with experimental time-lapse microscopy, with engulfment sensitive to the number of SpoIIQ-SpoIIIAH bonds in a threshold-like manner. Indeed, decreasing the medium osmolarity in experiments prevents engulfment in line with predictions.