Effect of Combined Physical Stresses on Cells: The Role of Water

Abstract : The role of water in microorganism viability was assessed through the application of combined physical perturbations. The combination of different physical parameters could allow to balance the properties variations (especially water related) resulting from the increase of one parameter alone. Thus, it is possible to optimize the survival of cells in controlling these parameters. This was tested through two different examples. The first example shows that combination of osmotic level and temperature can allow optimizing yeast cell survival in following membrane fluidity variation. Moreover this analysis has allowed a better comprehension of cell inactivation during rehydration and especially the impact of intracellular vesiculation during dehydration. The second example deals with the effect of combination of high hydrostatic pressure, low temperature and water activity of the medium, on resistance Escherichia coli cells. These experiments show that synergetic effect of high pressure and low temperature was only observed at pressure lower than 300 MPa and high water content. Otherwise, low temperature as well as low water activity protects the microorganisms from inactivation even at extreme pressure level (P > 600 MPa). These two examples show the implication of water thermodynamical properties and their preservation on cell survival even after extreme treatment conditions. Preservations process would certainly benefit from extensions of this knowledge.