Anaerobic nutrition of Saccharomyces cerevisiae. II. Unsaturated fatty acid requirement for growth in a defined medium

Effect of dissolved oxygen, temperature, initial cell count, and sugar concentration on the viability of Saccharomyces cerevisiae in rapid fermentations

By using 7 x 10(8) cells of Saccharomyces cerevisiae per ml with which 25 degrees Brix honey solutions were fermented to 9.5% (wt/vol; 12% vol/vol) ethanol in 2.5 to 3 h at 30 C, i.e., rapid fermentation, the death rate was found to be high, with only 2.1% of the yeast cells surviving at the end of 3 h under anaerobic conditions. As the dissolved oxygen in the medium was increased from 0 to 13 to 20 to 100% in rapid fermentations at 30 C, there was a progressive increase in the percentage of cells surviving. The ethanol production rate and total were not seriously affected by a dissolved oxygen concentration of 13%, but fermentation was retarded by 20% dissolved oxygen and still further decreased as the dissolved oxygen content reached 100%. When the fermentation temperature was decreased to 15 C (at 13% dissolved oxygen), the rate of fermentation decreased, and the fermentation time to 9.5% ethanol (wt/vol) increased to 6 h. It was found that the higher the temperature between 15 and 30 C, the greater the rate of death as initial cell counts were increased from 1.1 x 10(7) to 7.8 x 10(8) cells per ml. At the lowest level of inoculum, 1.1 x 10(7) cells per ml, there was actual multiplication, even at 30 C; however, the fermentation was no longer rapid. The addition of 15% sugar, initially followed after an hour by the remaining 10%, or addition of the sugar in increments of 2.5 or 5% yielded a better survival rate of yeast cells than when the fermentation was initiated with 25% sugar.

Biochemical and genetic aspects of nystatin resistance in saccharomyces cerevisiae

Two phenotypically distinct sets of nystatin-resistant mutants were investigated. One set is resistant, respiratory competent, and requires no lipid for growth. The other set is more resistant, respiratory deficient, and lipid requiring (unsaturated fatty acid or sterol). Both sets show altered sterol composition as demonstrated by the Liebermann-Burchard colorimetric reaction, ultraviolet spectrophotometry, and gas-liquid chromatography. Genetic analysis indicates that all nystatin-resistant mutants can be placed into one of six distinct genetic groups. The phenotype's nystatin resistance, lipid requirement, and respiratory deficiency are recessive. There was one case of allelism for mutants from different sets. Revertants of mutants which have the tripartite phenotype retain a residual level of nystatin resistance, but they are no longer lipid requiring or respiratory deficient. Growth studies in mutants which have the tripartite phenotype reveal that the addition of ergosterol to the growth medium results in decreased resistance to nystatin.

Effect of unsaturated fatty acids on the development of respiration and on protein synthesis in an unsaturated fatty acid mutant of Saccharomyces cerevisiae

The extent of development of respiratory function induced by aeration of an anaerobically grown unsaturated fatty acid auxotroph of Saccharomyces cerevisiae is determined by the availability, endogenous or externally supplied, of unsaturated fatty acid. The synthesis of mitochondrial and cytoplasmic enzymes during aeration appears to have a similar basis of regulation by available unsaturated fatty acid. Levels of unsaturated fatty acid that permit the synthesis of mitochondrial enzymes also result in a substantial stimulation of cellular protein synthesis.

Fatty acid and sterol composition of Mucor genevensis in relation to dimorphism and anaerobic growth

Fatty acid and sterol content and composition were determined for the dimorphic mold, Mucor genevensis, grown under a variety of experimental conditions. Fatty acids account for 6 to 9% of the dry weight of aerobically grown mycelium, and 70 to 80% of these are unsaturated. The organism contains gamma-linolenic acid which is characteristic for Phycomycetes, and in sporangiospores this compound represents 40% of the total fatty acids. Of the sterols found in mycelium, 80% is ergosterol, and stigmasterol was positively identified as one of the minor components. In anaerobically grown yeastlike cells, sterol content is less than 10% of the level found in aerobically grown cells, and fatty acids amount to less than 2% of the dry weight. These fatty acids are predominantly short chain and less than 10% are unsaturated. Yeastlike cells obtained under aerobic conditions by growth in the presence of phenethyl alcohol have fatty acid and sterol compositions characteristic of aerobically grown mycelium. It is concluded that the dimorphology of the organism is not directly related to lipid composition.

Nutritional requirements for growth and yeastlike development of Mucor rouxii under carbon dioxide

Unlike five other strains of Mucor rouxii previously studied, certain nutritional factors must be present for rapid growth and completely yeastlike development of M. rouxii (National Regional Research Laboratory 1894) under CO(2); high CO(2) tensions markedly inhibit growth of this strain. Addition of yeast extract, peptone, or enzymatically hydrolyzed casein in substrate amounts to a basal medium (containing acid-hydrolyzed casein) completely relieved CO(2) inhibition of growth and permitted yeastlike development. The "CO(2) growth factor" activity of these supplements proved to be dialyzable and acid labile. These findings, together with the results of gel filtration and amino acid analysis, suggested that CO(2) growth factor activity can be attributed to small peptides.

Fatty-acid composition of Candida utilis as affected by growth temperature and dissolved-oxygen tension

Analyses were made of the fatty-acid composition of Candida utilis NCYC 321 grown in a chemostat at a dilution rate (equal to growth rate) of 0.1 hr(-1) and at temperatures in the range of 30 to 15 C and dissolved oxygen tensions between 75 and <1 mm of Hg. Cells grown under glucose limitation or NH(4) (+) limitation contained mainly C(16:0), C(16:1), C(18:0), C(18:1), C(18:2), and C(18:3) acids as detected by gas-liquid chromatography of methyl esters of the acids from lipids extracted with chloroform-methanol. The relative proportions of these acids varied with the growth temperature and the dissolved-oxygen tension in the culture. A decrease in growth temperature from 30 to 20 C led to an increased synthesis of unsaturated acids in cells grown under either limitation at a fixed-oxygen tension in the range of 75 to 5 mm of Hg. In cultures with a dissolved-oxygen tension of 1 and <1 mm of Hg, a further decrease in temperature to 15 C caused an increased synthesis of unsaturated fatty acids. A decrease in dissolved-oxygen tension led to a diminished synthesis of unsaturated fatty acids in cells grown at a fixed temperature under either limitation. Cells grown at a fixed temperature under glucose limitation synthesized a greater proportion of C(16) acids at the expense of C(18) acids as the dissolved oxygen tension was decreased from 75 to <1 mm of Hg. A preferential synthesis of C(16) acids also occurred as the growth temperature was decreased from 30 to 15 C in cells grown under glucose limitation at a fixed-oxygen tension. The same effect was observed in cells grown under NH(4) (+) limitation when the temperature was lowered from 30 to 20 C; but when the temperature was decreased further to 15 C, the cells synthesized a slightly greater proportion of C(18) acids. Synthesis of a large proportion of C(16) acids was accompanied by an excretion of pyruvate, and occasionally traces of 2-ketoglutarate, and an increased intracellular accumulation of certain amino acids.

The biogenesis of mitochondria. 3. The lipid composition of aerobically and anaerobically grown Saccharomyces cerevisiae as related to the membrane systems of the cells

The growth conditions known to influence the occurrence of mitochondrial profiles and other cell membrane systems in anaerobic cells of S. cerevisiae have been examined, and the effect of the several growth media on the lipid composition of the organism has been determined. The anaerobic cell type containing neither detectable mitochondrial profiles nor the large cell vacuole may be obtained by the culture of the organism on growth-limiting levels of the lipids, ergosterol, and unsaturated fatty acids. Under these conditions, the organism has a high content of short-chain saturated fatty acids (10:0, 12:0), phosphatidyl choline, and squalene, compared with aerobically grown cells, and it is especially low in phosphatidyl ethanolamine and the glycerol phosphatides (phosphatidyl glycerol + cardiolipin). The high levels of unsaturated fatty acids normally found in the phospholipids of the aerobic cells are largely replaced by the short-chain saturated acids, even though the phospholipid fraction contains virtually all of the small amounts of unsaturated fatty acid present in the anaerobic cells. Such anaerobic cells may contain as little as 0.12 mg of ergosterol per g dry weight of cells while the aerobic cells contain about 6 mg of ergosterol per g dry weight. Anaerobic cell types containing mitochondrial profiles can be obtained by the culture of the organism in the presence of excess quantities of ergosterol and unsaturated fatty acids. Such cells have increased levels of total phospholipid, ergosterol, and unsaturated fatty acids, although these compounds do not reach the levels found in aerobic cells. The level of ergosterol in anaerobic cells is markedly influenced by the nature of the carbohydrate in the medium; those cells grown on galactose media supplemented with ergosterol and unsaturated fatty acids have well defined mitochondrial profiles and an ergosterol content (2 mg per g dry weight of cells) three times that of equivalent glucose-grown cells which have poorly defined organelle profiles. Anaerobic cells which are low in ergosterol synthesize increased amounts of squalene.

The biogenesis of mitochondria. II. The influence of medium composition on the cytology of anaerobically grown Saccharomyces cerevisiae

Yeast cells grown anaerobically have been shown to vary in their ultrastructure and absorption spectrum depending upon the composition of the growth medium. The changes observed in the anaerobically grown cells are governed by the availability of unsaturated fatty acids and ergosterol and a catabolite or glucose repression. All the cells contain nuclear and plasma membranes, but the extent of the occurrence of vacuolar and mitochondrial membranes varies greatly with the growth conditions. Cells grown anaerobically on the least nutritive medium, composed of 0.5% Difco yeast extract-5% glucose-inorganic salts (YE-G), appear to contain little vacuolar membrane and no clearly recognizable mitochondrial profiles. Cells grown anaerobically on the YE-G medium supplemented with Tween 80 and ergosterol contain clearly recognizable vacuolar membrane and some mitochondrial profiles, albeit rather poorly defined. Cells grown on YE-G medium supplemented only with Tween 80 are characterized by the presence of large amounts of cytoplasmic membrane in addition to vacuolar membrane and perhaps some primitive mitochondrial profiles. When galactose replaces glucose as the major carbon source in the medium, the mitochondrial profiles within the cytoplasm become more clearly recognizable and their number increases. In aerobically grown cells, the catabolite repression also operates to reduce the total number of mitochondrial profiles. The possibility is discussed that cells grown anaerobically on the YE-G medium may not contain mitochondrial membrane and, therefore, that such cells, on aeration, form mitochondrial membrane from nonmitochondrial sources. A wide variety of absorption compounds is observed in anaerobically grown cells which do not correspond to any of the classical aerobic yeast cytochromes. The number and relative proportions of these anaerobic compounds depend upon the composition of the growth medium, the most complex spectrum being found in cells grown in the absence of lipid supplements.

The evolution of oxygen as a biosynthetic reagent

THE BIOSYNTHESIS OF CERTAIN CELL CONSTITUENTS: monounsaturated fatty acids, tyrosine, and nicotinic acid, is oxygen-dependent in many higher organisms. The same compounds can be synthesized by different, oxygen-independent pathways in lower organisms. The general outlines of these pathways are described and the importance of the compounds synthesized is discussed. An examination of the distribution of these pathways among living organisms reveals that oxygen-dependent pathways replaced the "anaerobic" pathways at different branch points on the evolutionary tree. Other groups of compounds are discussed, which are not distributed as widely among living organisms, but are found in all higher organisms. These compounds have specialized functions and their biosynthesis requires molecular oxygen. The oxygen-dependent portions of the biosynthetic pathways leading to porphyrins, quinone coenzymes, carotenoids, sterols, and polyunsaturated fatty acids are summarized. The distribution and functions of these compounds are also considered and an attempt is made to place them in the framework of evolution. While sterols and polyunsaturated fatty acids are found exclusively in the higher Protista and multicellular organisms, carotenoids, porphyrins, and quinones are also found in bacteria. The possibility of oxygen-independent mechanisms for their biosynthesis is discussed.

ANAEROBIC GROWTH OF FUSARIUM OXYSPORUM

Gunner , H. B. (Cornell University, Ithaca, N.Y.), and M. Alexander . Anaerobic growth of Fusarium oxysporum . J. Bacteriol. 87: 1309–1316. 1964.— Fusarium oxysporum , an alleged obligate aerobe, was found to be capable of growth in the absence of molecular oxygen, provided the medium contained yeast extract, MnO 2 , nitrate, selenite, or ferric ions. The active substance in yeast extract was not identified. The fungus possessed hydrogenase, and was capable of utilizing H 2 . Under anaerobic conditions, the fungus effected the reduction of nitrate, ceric, ferric, selenite, and tellurite ions, as well as the reduction of several inorganic sulfur compounds and indicators having positive oxidation-reduction potentials. The products of anaerobic nitrate-dependent growth were ethanol, CO 2 , acetic acid, and ammonia. Possible explanations for the apparent inability of obligate aerobes to grow in the absence of O 2 are discussed.

SOME FACTORS AFFECTING STEROL FORMATION IN SACCHAROMYCES CEREVISIAE

Starr, Patricia R. (Oregon State University, Corvallis) and L. W. Parks . Some factors affecting sterol formation in Saccharomyces cerevisiae . J. Bacteriol. 83: 1042–1046. 1962.—A wild-type diploid strain of Saccharomyces cerevisiae was used in a study of factors that influence sterol synthesis. Maltose, glucose, sodium acetate, and ethanol were shown to be readily available for sterol synthesis in growing cultures of yeast. In cells grown anaerobically and then exposed to various substrates in aerobic resting-cell suspension, only glucose and ethanol stimulated ergosterol formation. Under these conditions, sterol synthesis was directly proportional to the amount of glucose provided. Sulfanilamide decreased the yield of sterol in growing cells, but had no effect on sterol synthesis by resting cultures.