Osmotic stress response in C . glutamicum : impact of channel- and transporter-mediated potassium accumulation
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ORIGINAL PAPER
Osmotic stress response in C. glutamicum: impact of channeland transporter-mediated potassium accumulation Ines Ochrombel • Markus Becker Reinhard Kra¨mer • Kay Marin
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Received: 16 March 2011 / Revised: 6 May 2011 / Accepted: 9 May 2011 / Published online: 26 May 2011 Ó Springer-Verlag 2011
Abstract Potassium accumulation is an essential aspect of bacterial response to diverse stress situations; consequently its uptake plays a pivotal role. Here, we show that the Gram-positive soil bacterium Corynebacterium glutamicum which is employed for the large-scale industrial production of amino acids requires potassium under conditions of ionic and non-ionic osmotic stress. Besides the accumulation of high concentrations of potassium contributing significantly to the osmotic potential of the cytoplasm, we demonstrate that glutamate is not the counter ion for potassium under these conditions. Interestingly, potassium is required for the activation of osmotic stress-dependent expression of the genes betP and proP. The Kup-type potassium transport system which is present in C. glutamicum in addition to the potassium channel CglK does not contribute to potassium uptake at conditions of hyperosmotic stress. Furthermore, we established a secondary carrier of the KtrAB type from C. jeikeium in C. glutamicum thus providing an experimental comparison of channel- and carrier-mediated potassium uptake under osmotic stress. While at low potassium availability, the presence of the KtrAB transporter improves both potassium accumulation and growth of C. glutamicum upon osmotic stress, at proper potassium supply, the channel CglK is sufficient.
Communicated by Erko Stackebrandt.
Electronic supplementary material The online version of this article (doi:10.1007/s00203-011-0717-6) contains supplementary material, which is available to authorized users. I. Ochrombel M. Becker R. Kra¨mer K. Marin (&) Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany e-mail: [email protected]
Keywords
CglK KtrAB Gene expression C. jeikeium
Introduction An efficient response to osmotic stress is essential for bacteria in natural habitats as well as during their biotechnological application. In nature, water availability can be low because of drought or increased salt concentration thereby representing an osmotic challenge (Bremer and Kra¨mer 2000). In biotechnology, high concentrations of both nutrients and products in the fermentation broth may cause osmotic stress affecting the production rate and the product yield (Varela et al. 2003). Osmotic stress by nonionic substances causes the efflux of water out of the cell, osmotic stress by salts, in addition, may be accompanied by the influx of ions. The bacterial response towards osmotic stress represents a multiphasic adjustment comprising ion transport processes as well as the accumulation of compatible solutes (Bremer and Kra¨mer 2000; Reed et al. 1985; Wood 1999). These solutes are low molecular weight compounds, frequently metabolic end products, t
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