Euglena gracilis as a promising eukaryotic model system for fast detection of high pressure induced cell destruction

High hydrostatic pressure (HHP) is a promising method for the inactivation of cells and enzymes in many applications (e.g. food industry, pharmaceutical industry, chemistry). The effects of various high-hydrostatic pressures (20 MPa, 50 MPa, 55 MPa, 60 MPa, 75 MPa, 100 MPa, 150 MPa, 200 MPa, 400 MPa) on the unicellular flagellate Euglena gracilis were determined: (a) life/dead staining with ethidium bromide (EtBr), (b) loss of flagellum, (c) movement behavior, (d) recovery after 7 d, (e) photosystem II quantum yield (Y(PSII)). Pressure was applied for 300 s at room temperature (pressure increment and decrement: 10 MPa s−1). The EC50 value of vitality (EtBr-positive cells) directly after pressure application was 109 MPa. Cell vitality was not impaired below 100 MPa. No recovery of cells after 7 d-cultivation in fresh medium was observed after pressure treatment above 100 MPa. Flagellum-based free swimming of cells was already impaired at pressures above 50 MPa, where some cells started metabolic movement behavior. From 75 MPa to 100 MPa all cells moved metabolically, while at higher-pressure all cells became immotile. In the pressure range between 75 MPa and 200 MPa, cells lost their flagellum. Interestingly, cells pressurized with 400 MPa retained their flagella. Directly after HHP-treatment EC50 of Y(PSII)-inhibition was about 101 MPa, after 6 h about 102 MPa. The use of fluorescence-based methods is considerably fast, easy and reliable. Because of the different easily recordable parameters, we believe that Euglena gracilis is a promising test organism to determine HHP-effects on eukaryotes. The effects on photosynthesis indicate impacts on intracellular membrane and protein complexes.