High hydrostatic pressure (HHP) exerts manifold effects on cells and microorganisms, leading to adaptation, stress response and cell death. HHP affects all levels of cellular physiology targeting cellular organization, transcription, translation, protein conformation, enzyme activity and membrane function. The group uses HHP to study cellular processes and molecular responses in bacterial and eukaryotic systems. The HHP response of Lactobacillus sanfranciscensis and Escherichia coli was studied in proteomic and transcriptomic approaches. Also, HHP induced mutants were characterized. Two major effectors of the pressure response were identified. Overexpression of ssr confers enables growth under high pressure by helping to maintain ribosomal function in L. sanfranciscensis. The restriction endonuclease mrr, specifically cleaving methylated DNA appears as a major mediator of the high pressure response in E. coli. Primary HHP targets were identified to be the cellular membrane and the ribosome. Many other stress responses observed appear to be secondary effects. Translation is stalled above 40 MPa. Ribosomes can be returned to functionality by trans-translation and peptide tagging mediated by tmRNA and the ClpX. These are turned on as a specific reaction of HHP stress. These systems can now be studied in close collaboration. Furthermore, the high pressure triggered expression of genes encoding pathogenicity factors is studied offering joint research. The eukaryotic systems investigated are muscle cells and chondrocytes. As a result of their larger size as compared to bacteria, they are valuable models in using pressure as a tool in cell biology. The availability of recombinant cell lines expressing green fluorescent protein/fusions can be used to study distribution and aggregation of proteins in situ under pressure. HHP microscopy facilities were used in collaborative investigations to study muscle cells and their ion channels under pressure in situ.

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1. High Pressure Tuning of Biochemical Processes: Macromolecular Interactions and Cellular Physiology