Adaptation of Corynebacterium glutamicum to salt-stress conditions.

Corynebacterium glutamicum is one of the biotechnologically most important microorganisms because of its ability to enrich amino acids extracellularly. Hence, C. glutamicum requires effective adaptation strategies against both hypo- and hyperosmotic stress. We give a comprehensive and coherent outline about the quantitative dynamics of C. glutamicum during adaptation to hyperosmotic stress at the transcript and protein levels. The osmolyte carrier ProP, playing a pivotal role in hyperosmotic stress defence, exhibits the strongest up-regulation of all proteins. A conspicuously regulated group comprises proteins involved in lipid biosynthesis of the cell envelope. This is in accordance with our observation of a more viscous and stickier cell envelope, which is supported by the findings of an altered lipid composition. Together with our results, showing that several transporters were down-regulated, this membrane adaptation appears to be one of C. glutamicum's major protection strategies against hyperosmotic stress. In addition, we demonstrate that no oxidative stress and no iron limitation occur during salt stress contrary to former postulations. Ultimately, it is remarkable that various proteins with divergent mRNA-protein dynamics and regulation have been observed. This leads to the assumption that there are still unknown mechanisms in between the bacterial transcription, translation and post-translation and that these are waiting to be unravelled.