Abstract
The importance of the physiological state of a culture of Saccharomyces cerevisiae for tolerance to sudden osmotic dehydration was studied, and it was investigated whether specific osmotolerance factors were demonstrable. The microcalorimeter was used to monitor growth, and different physiological states of the culture were selected and their osmotolerance was tested. In addition to cells in the stationary phase, cells from the transition phase between respirofermentative and respiratory catabolism were osmotolerant. S. cerevisiae exhibited ever-changing metabolism during batch growth on either glucose or ethanol as the carbon source. Instantaneous heat production per biomass formation (dQ/dX) and specific activity of sn-glycerol 3-phosphate dehydrogenase (GPDH) (EC 1.1.1.8) were shown to differ for different physiological states. Neither high respiratory activity nor low total cellular activity, nor factors involved in osmoregulation, i.e., intracellular glycerol or activity of GPDH, correlated with the osmotolerant phenotype.
Highlights
Different species of yeast vary considerably in response to reduced water activity
This technique allows measurements of the heat production rate of the culture, which is related to the amount of biomass, the kind of metabolism used, the rate of growth, and the energy spent on reactions not directly coupled to biosynthesis [5, 13]
During the first phase of growth, glucose was consumed, and ethanol, together with small amounts of glycerol and acetate, was produced (Fig. 1A, C, and D). For most of this glucose-consuming phase, the heat production rate increased in parallel with the biomass (Fig. 1A), which resulted in a specific heat production rate of ca. 770 p.W/mg
Summary
The heat production rate (dQldt) was measured with a multichannel microcalorimeter (Bioactivity Monitor LKB 2277) of the heat conduction type [28], fitted with three channels, each equipped with a flowthrough cell to permit simultaneous recording of three cultures. Colony-forming capacity was measured on YEPD plates (1% yeast extract, 2% peptone, 2% glucose, 2% agar) with appropriate amounts of NaCl added to give final concentrations of 0, 1.0, 1.4, and 1.5 M NaCl. Culture samples were mixed vigorously (Vortex tube mixer) and serially diluted in 0.9% (wt/vol) NaCl solution, and 100-,ul portions were spread on plates containing the various NaCl concentrations. Concentrations of glucose, ethanol, glycerol, and acetate were analyzed by using enzyme combination kits (Biochemica Test Combination; Boehringer Mannheim GmbH, Mannheim, Federal Republic of Germany).
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