, 2005), on freeze-drying of yeast, which usually leads to comparatively small viability of cells (Leslie et al., 1994) as well as at convective air drying with a high viability of dry cells (Rapoport et al., 2009). It is known that phospholipid bilayers of membranes temporarily

become more permeable at such phase transitions (Crowe et al., 1989a, b; Hoekstra et al., 1992). In turn, increases in cell membrane permeability and leakage of intracellular substances can lead to their death. Because the value of Tm becomes minimal at water contents around 20–25% (Crowe et al., 1989a, b; Hoekstra et al., 1992), preliminary cell rehydration in water vapour (during which its relative humidity increases to 20–28%) leads to reduced cell leakage and correspondingly increased viability of yeast cells that are rehydrated LY2157299 research buy from a dry state (see Tables 2 and 3). The results in Table 2 show that the viability of rehydrated exponentially grown yeast cells that were grown in media with different concentrations of Mg2+ can be improved using a gradual rehydration

procedure. The best viability following slow rehydration of cells was maintained when yeast cells were grown before dehydration in media with Mg2+ at 0.15 g L−1. The finding, as opposed to rapid rehydration, testifies to aberrant changes GDC0068 in yeast membranes. Therefore, it is apparent that cell death during dehydration–rehydration is linked to membrane damage, and this may partly explain the extreme sensitivity of actively growing cells to dehydration treatments. Moreover,

these results indicate that Mg2+ ions in a nutrient medium can confer some degree of membrane protection in the face of water stress. Recently, a negative correlation was shown between the Protein kinase N1 overall fluidity variation undergone by membranes during treatments and yeast cell survival. Minimization of fluidity fluctuations significantly increased yeast survival (Simonin et al., 2008). Taking into account that Mg2+ may charge-stabilize membrane phospholipids, which concomitantly stabilizes the lipid bilayer and decreases membrane fluidity (Walker, 1999), we infer that magnesium can similarly reduce fluidity fluctuations. Table 2 shows the results of experiments with dehydrated stationary-phase yeast cells, and in this case, there is a significant effect of magnesium (at 0.15 g L−1) on the maintenance of viability during a slow rehydration process. Therefore, optimum media magnesium concentrations are important for stabilization of intracellular membranes. Recently, Rodriguez-Porrata et al. (2008) showed positive effects of magnesium in a rehydration medium in experiments with dry wine yeast. As discussed previously, the increased bioavailability of Mg2+ during rehydration may probably protect plasma membrane integrity by a charge neutralization of membrane phospholipids.