CeBiTec – Colloquium
Tuesday, 23 January, 2017, 17 c.t.
G2-104, CeBiTec Building
Prof. Dr. Erhard Bremer
Dept. of Biology, Molecular Microbiology, Philipps-University Marburg
LOEWE-Center for Synthetic Microbiology, Philipps-University Marburg
The big fight: systems-wide stress responses to osmotic challenges
The development of a semi-permeable cytoplasmic membrane through which water can pass freely, but ions, nutrients and waste products cannot, was a key event in the evolution of microbial proto-cells. Changes in the external osmolarity (or salinity) will inevitably trigger water fluxes along the osmotic gradient across this membrane. As a consequence, cellular integrity and magnitude of turgor will be affected. Water influx at low external osmolarity prompts a raise in turgor that can result in cell rupture. Conversely, high external osmolarity triggers water efflux and thereby causes dehydration of the cytoplasm; growth will be arrested. Obviously, timely stress responses have to be mounted by bacterial cells to avoid such catastrophic events. In its varied habitats, Bacillus subtilis is frequently exposed to fluctuations in the external osmolarity (e.g., through desiccation and flooding of the soil). I will present an overview of the cellular stress reactions of this ubiquitously distributed Gram-positive bacterium to osmotic challenges, which allows the cells to survive exposures to either low or high osmolarity souroundings. I will describe the synthesis pathways and the genetics for the osmostress-relieving production of the compatible solutes L-proline and glycine betaine, the operation of importers for osmostress protectants at high salinity and their salient structural features, and I will address their release via MscS- and MscL-type mechanosensitive channels upon an osmotic down-shock. Finally, I will present data connecting the osmotic stress responses of free-living cells with key regulatory factors controlling life of B. subtilis in biofilms.
Host: Prof. Dr. Volker Wendisch