Accessible Requires Authentication Published by De Gruyter December 8, 2016

Guardians in a stressful world: the Opu family of compatible solute transporters from Bacillus subtilis

Tamara Hoffmann and Erhard Bremer
From the journal Biological Chemistry

Abstract

The development of a semi-permeable cytoplasmic membrane was a key event in the evolution of microbial proto-cells. As a result, changes in the external osmolarity will inevitably trigger water fluxes along the osmotic gradient. The ensuing osmotic stress has consequences for the magnitude of turgor and will negatively impact cell growth and integrity. No microorganism can actively pump water across the cytoplasmic membrane; hence, microorganisms have to actively adjust the osmotic potential of their cytoplasm to scale and direct water fluxes in order to prevent dehydration or rupture. They will accumulate ions and physiologically compliant organic osmolytes, the compatible solutes, when they face hyperosmotic conditions to retain cell water, and they rapidly expel these compounds through the transient opening of mechanosensitive channels to curb water efflux when exposed to hypo-osmotic circumstances. Here, we provide an overview on the salient features of the osmostress response systems of the ubiquitously distributed bacterium Bacillus subtilis with a special emphasis on the transport systems and channels mediating regulation of cellular hydration and turgor under fluctuating osmotic conditions. The uptake of osmostress protectants via the Opu family of transporters, systems of central importance for the management of osmotic stress by B. subtilis, will be particularly highlighted.

Acknowledgments

Financial support for our studies on the osmostress response systems of B. subtilis was provided over the years by the Deutsche Forschungsgemeinschaft (DFG), the LOEWE excellence program of the state of Hessen via the Center for Synthetic Microbiology (Synmicro; University of Marburg, Germany), the Bundesministerium für Bildung und Forschung (BMBF) through the consortium BaCell-SysMo2, and the Fonds der Chemischen Industry (FCI). As always, we greatly value the expert help of Vickie Koogle in the language editing of our manuscript. We profoundly thank our colleagues Lutz Schmitt and Sander Smits (University of Düsseldorf; Germany), Michael Hecker and Uwe Völker (University of Greifswald; Germany), and Jörg Stülke and Fabian Commichau (University of Göttingen; Germany) for inspiring and long-term collaborations on the ‘ins and outs’ of the systems-wide responses of B. subtilis to osmotic stress and the analysis of the transporters, which are at the core of it.

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Received: 2016-8-8
Accepted: 2016-8-29
Published Online: 2016-12-8
Published in Print: 2017-2-1

©2017 Walter de Gruyter GmbH, Berlin/Boston