Arch Microbiol (1991) 156:38-42 0302893391000924 Archives of Microbiology © Springer-Verlag 1991 Metabolic changes induced during adaptation of Saccharomyces cerevisiae to a water stress Keshav K. Singh 1 and R. S. Norton 2 1 Department of Biology, The University of Wollongong, Wollongong, NSW 2500, Australia 2 School of Biochemistry, University of New South Wales, Kensington, NSW 2033, Australia Received August 8, 1990/Accepted March 5, 1991 Abstract. When exponentially growing Saccharomyces cerevisiae was transferred from a normal high water ac- tivity growth medium (aw 0.997) to a medium containing 8% NaC1 low water activity growth medium (aw 0.955), glycerol accumulation during the first eight hours of the adaptation was both retarded and greatly diminished in magnitude. Investigation of the underlying reasons for the slow onset of glycerol accumulation revealed that not only was overall glycerol production reduced by salt transfer, but also the rates of ethanol production and glucose consumption were reduced. Measurement of gly- colytic intermediates revealed an accumulation of glu- cose-6-phosphate, fructose-6-phosphate, fructose 1,6 bis- phosphate and phosphoenolpyruvate in S. cerevisiae 3 to 4 h after transfer to salt, suggesting that one or more glycolytic enzymes were inhibited. Potassium ions ac- cumulated in S. cerevisiae after salt transfer and reached a maximum about 6 h after transfer, whereas the sodium ion content increased progressively during the adaptation period. The trehalose content also increased in adapting cells. It is suggested that inhibition of glycerol production during the initial period of adaptation could be due to either the inhibition of glycerol-3-phosphate dehydrogen- ase by increased cation content or the inhibitin of glycoly- sis, glycerol being produced glycolytically in S. cerevisiae. The increased accumulation of glycerol towards the end of the 8-h period suggests that the osmoregulatory re- sponse of S. cerevisiae involves complex sets of adjust- ments in which inhibition of glycerol-3-phosphate de- hydrogenase must be relieved before glycerol functions as a major osmoregulator. Key words: Water stress - Saccharomyces cerevisiae - Glycerol - Yeast water relations - Osmoregulation Offprint requests to present address: Department of Immunology and Medical Microbiology, College of Medicine, Box J-266, JHMHC, University of Florida, Gainesville, Florida 32610, USA The study of yeast water relations has concentrated on three organisms, namely halotolerant Debaryomyces hansenii (Adler et al. 1985), xerotolerant Saccharomyces rouxii (Onishi and Siromaru 1984; Edgley and Brown 1983) and nontolerant S. cerevisiae (Edgley and Brown 1983; Mackenzie et al. 1986; Mackenzie et al. 1988). The areas of investigations have so far focussed mainly on the steady-state situations, that is when yeast has fully adapted to a water stress (Adler et al. 1985; Lindman and Norkrans 1982; Brown and Edgley 1980). However, very few studies have been done during the period of adap- tation of yeast to the water stress. Edgley and Brown (1983) have compared the physiological changes induced by a water stress in nontolerant S. cerevisiae and xerotolerant S. rouxii during the adaptation period. Their results suggest that growth of S. cerevisiae at low water activity dramatically increases the activity of glycerol-3- phosphate dehydrogenase, but not until 40 h later, whereas this enzyme in S. rouxii remained unaffected. With a view to understanding further the biochemical adjustment that must be made when S. cerevisiae is sub- jected to a water stress, in this study the glycerol content of S. eerevisiae was monitored during the early stages of adaptation to liquid medium containing salt. The yeast did not begin to accumulate glycerol until about 6 h after transfer. Glycerol is produced glycolytically in S. cerevisiae (Brown and Edgley 1980), so that the osmoregulatory response is likely to be closely integrated with glycolysis. The levels of phosphorylated glycolytic intermediates, nucleotides and ions were quantified in order to identify the intracellular event(s) limiting glycerol production during the initial critical period of adaptation. Materials and Methods Yeast strains S. cerevisiae (strain Y41, ATCC 38531) described by Anand and Brown (1968) was maintained at 4°C on slopes of malt extract agar (MA; 0.997).