Slow gradual rehydration of the dry yeast was accomplished by incubation in water vapour in a chamber (over distilled water) at 37 °C for 1 h. All experiments were performed in five replicates, and mean figures with SD are presented. Although it has been shown previously that Mg2+ and Ca2+ ions play important roles in yeast cells’ physiological and check details biotechnological characteristics (Walker, 1994, 1999, 2004), there is no information regarding the influence of these metal ions on yeast resistance to dehydration–rehydration. We therefore firstly studied the effects of magnesium and calcium on yeast biomass yield, before
investigations of anhydrobiosis phenomena. Molasses was chosen as a rich growth medium because we have previously found that this resulted in yeast biomass with a rather high resistance to dehydration. In addition, we conducted experiments in molasses-based media because it is widely used as an industrial fermentation medium for both yeast biomass and ethanol production. Metal ion concentrations are known to vary significantly in molasses received from various sources (Walker, 1994).We therefore
adjusted the mineral GSI-IX composition of molasses in yeast growth experiments to ascertain the influence of altered magnesium and calcium bioavailabilities. In this study, we used the same batch of molasses and artificially elevated magnesium and calcium to levels in excess of their basal concentrations (see Walker, 1999). Beet molasses-based nutrient media contained low concentrations of magnesium and calcium ions compared with the supplementary quantities used in our experiments. The mean concentrations of magnesium and calcium in these media are 67 and 750 mg L−1, respectively (Wolniewicz et al., 1988; Walker, AMP deaminase 1994). Supplementary levels of magnesium were 150 and 300 mg L−1 and those of calcium were 2000 and 5000 mg L−1. Therefore, we initially attempted to reveal whether these levels of magnesium and calcium influenced yeast growth and biomass yield.
Figure 1 shows that the maximum accumulation of biomass in the exponential growth phase of the culture was reached when the magnesium content in the medium was 0.75 g L−1 MgSO4 (corresponding to 0.15 g L−1 Mg2+). Magnesium supplementation to stationary-phase cultures had no effect on biomass yields. With regard to calcium, increasing the availability of this metal in the medium led to an increase in the total biomass yield in both the exponential and the stationary phases of culture growth, with the most significant effect being revealed in the exponential phase of culture growth. We investigated the influence of Mg2+ and Ca2+ ions on yeast cell resistance to dehydration. For the determination of yeast cell viability, we used the fluorochrome, primuline.