Kenneth Watson

Mitochondrial and cytoplasmic protein syntheses are not required for heat shock acquisition of ethanol and thermotolerance in yeast

Heat shock acquisition of ethanol‐ and thermotolerance in Saccharomyces cerevisiae was not inhibited in cells incubated in the presence of cycloheximide or chloramphenicol. Respiratory‐deficient (ρ−) mutants also characteristically exhibited the heat shock response. It was concluded that mitochondrial and cytoplasmic protein syntheses are not required for heat shock acquisition of ethanol and thermotolerance in yeast.

Acquisition of ethanol tolerance in yeast cells by heat shock

SummaryThe experiments reported here show that heat shock treatment of a number of different strains ofSaccharomyces results in a marked increase in ethanol tolerance as compared to control cells. Our observations thus imply a relationship between the synthesis of heat shock proteins and the acquisition of ethanol tolerance in yeast.

Unsaturated fatty acid but not ergosterol is essential for high ethanol production in Saccharomyces

SummaryThe membrane lipid composition of Saccharomyces was manipulated by growing cells anaerobically with or without ergosterol and unsaturated fatty acid. Cells low in ergosterol but enriched in unsaturated fatty acid residues on membrane phospholipids produced high concentrations, 13–15.5% w/v, of ethanol at substrate conversion efficiencies of around 90%.

Leucosporidium Yeasts : Obligate Psychrophiles which Alter Membrane-lipid and Cytochrome Composition with Temperature

The temperature limits of growth of three psychorphilic yeasts, Leucosporidium frigidum, L. gelidum and L. nivalis, were examined. All species grew well as subzero temperatures (-I degrees C). The maximum temperature of growth was significantly higher with glucose as substrate (18 to 20 degrees C) than with ethanol (17 to 18 degrees C). There was a positive correlation between the growth temperature and the degree of fatty-acid unsaturation of the cell lipids; the lower the temperature, the greater the degree of fatty-acid unsaturation. At subzero temperatures (-I degrees C) with ethanol as substrate, 90% of the total fatty acid was unsaturated with linolenic (35 to 50%) and linoleic (25 to 30%) acids predominating. At temperatures close to the maximum for growth, linolenic acid accounted for less than 20% of the total fatty acid and oleic (20 to 40%) and linoleic (30 to 50%) acids were the major components. Difference spectra of intact cells showed marked changes in the rations and amounts of individual cytochromes as a function of growth temperature. In L.frigidum with glucose as substrate, the ratios of cytochromes a +a3:b:c at 8 and 19 degrees C were I:I-I:2-9 and I:2-3:16-7 respectively. Similar changes in cytochrome ratios were noted for L.gelidum, but changes were much less marked for L. nivalis. The temperature effects were interpreted as supporting the view that membrane structure and composition are fundamental to temperature adaptation in psychrophilic yeasts.

Naturally occurring respiratory deficient Candida slooffii strains resemble petite mutants

CYTOPLASMICALLY inherited respiratory deficient mutants termed petites, were first described in bakers yeast over 20 years ago1. Since then in laboratory studies several species of yeast have been shown to give rise to respiratory deficient mutants2,3. However, although some respiratory deficient (obligatory fermentative) yeasts have been found in nature3, it is not clear whether these species are the result of cytoplasmic (petite) or chromosomal lesions4 because no suitable genetic tests are available. Nevertheless it is known that petite mutants of both Saccharomyces cerevisiae5 and Tornlopsis glabrata6 have large deletions from their mitochrondrial DNA with each independent isolate having a unique circular DNA size profile which can be regarded as a ‘fingerprint’. By contrast chromosomal or segregational mutants have intact and functional mitochondrial DNA, as shown by genetic tests3,7,8. Therefore it seemed possible that the type of lesion in naturally occurring respiratory deficient species could be determined by circular DNA profile analysis. Using this method, we show here that three independently isolated strains of Candida slooffii resemble petite mutants.

Membrane Lipid Adaptation in Yeast

It is well recognized that the lipid composition of yeast varies with the growth conditions, and the reviews by Hunter and Rose (1971) and Rattray et al. (1975) should be consulted for references prior to 1975. A comprehensive review of the metabolism of sterols in yeast has been published (Parks, 1978).

BIOCHEMICAL AND MORPHOLOGICAL CORRELATIONS IN THE THERMOPHILIC ENTERIC YEASTS, SACCHAROMYCES TELLURIS, CANDIDA SLOOFFII, TORULOPSIS BOVINA and T. PINTOLOPESII

ABSTRACT Spontaneous respiratory-deficient mutants were isolated from the respiratory-competent thermophilic enteric yeasts, Torulopsis bovina and Saccharomyces telluris. A morphological and biochemical comparison was made of these yeasts with the naturally occurring respiratory-deficient thermophilic yeasts, Candida slooffii and T. pintolopesii. There were significant differences in cell size, temperature limits of growth and the effect of lipid supplement to the growth medium. Low temperature difference spectra revealed the presence of cytochromes aa 3 , b, c 1 and c in T. bovina and S. telluris , cytochromes b, c 1 and c in C. slooffii and T. pintolopesii and cytochromes c 1 and c in the spontaneous respiratory deficient mutants. A light buoyant density (1.6785-1.6870) DNA band was present in all the yeasts. The mitochondrial origin of this DNA was indicated by its selective elimination on treatment of cells with ethidium bromide. The latter result suggested that the respiratory-deficient yeasts were analogous to cytoplasmic petite , mutants of S. cerevisiae. Although classical assimilation and fermentation tests indicated that the spontaneous respiratory-deficient mutants were strains of T. pintolopesii , it was concluded, on the basis of marked morphological and biochemical differences, that this was not the case. KEYWORDS Torulopsis bovina ;, T. pintolopesii ;, Saccharomyces telluris ;, Candida slooffii ;, petite mutants;, thermophilic;, mitochondrial DNA.

Homeoviscous Adaptation in Psychrophilic, Meosphilic and Thermophilic Yeasts

Thermophilic and psychrophilic yeasts were differentiated on the basis of their ability, in the case of thermophiles, and inability, in the case of psychrophiles, to (a) grow under strictly anaerobic conditions and (b) produce stable respiratory-deficient mutants either spontaneously or on treatment with acriflavine or ethidium bromide. A possible correlation between these properties and the polyunsaturated fatty acid composition of the membrane phospholipids was proposed. There were marked changes in the fatty acyl composition of membrane phospholipids isolated from the thermophilic yeast, Torulopsis bovina, when monitored at different stages of growth under aerobic and anaerobic conditions. During aerobic induction of anaerobically grown cells, the direct desaturation of palmitic acid residues on phosphatidylcholine to palmitoleic acid appeared to be a mechanism whereby cells adjusted their membrane fluidity.