Showing papers on "Yeast published in 1976"

The utilization of sugars by yeasts.

Abstract: Publisher Summary This chapter outlines the breakdown of sugars by yeasts. To continue biosynthetic processes necessary for growth, yeasts obtain energy from sugars by breaking them down. The energy set free is stored as the “high energy” phosphate derivative adenosine 5’-triphosphate (ATP) that is synthesized as the sugar is catabolized. In catabolism, glycosidic bonds are hydrolyzed to yield component monosaccharides. A low concentration of oxygen is often important for obtaining a high yield of ethanol from certain sugars. Particularly in initial and terminal reactions, differences are found among different yeasts, and such relatively minor biochemical differences are often of considerable practical importance. The information provided in this chapter is based chiefly on studies yeast such as, Saccharomyces cerevisiae , Saccharomyces uvarum , Candida utilis , and Kluyveromyces fragilis . However, the ability of yeasts to utilize sugars is not only of potential value, it can also be a nuisance. Yeasts are notorious as spoilers of foods that contain a high concentration of one or more sugars, such as honey, maple syrup, sugar cane, and confectionery.

Structure and Biosynthesis of the Mannan Component of the Yeast Cell Envelope

Abstract: Publisher Summary The chapter focuses on the new developments concerning yeast mannan structure and biosynthesis as they relate to the organization of the cell wall and the roles played by these glycoproteins. The mechanism of mannan biosynthesis is still in a rudimentary state, partly because of the insufficient knowledge concerning mannan structure and partly because of the inherent difficulties in working with such a complex macromolecule. Detailed information of Saccharomyces cerevisiae mannan can now be sketched and facilitates the planning of experiments on, and the interpretation of results from, biosynthetic studies. Moreover, the availability of mannan mutants with known polysaccharide structural alterations should prove advantageous. Studies of mannan biosynthesis have taken three general tacks. One approach has been directed toward an elucidation of the overall process of mannan formation and translocation within the cell using “pulsechase” techniques and autoradiography. The second approach has dealt with the formation and secretion of intact mannan molecules by yeast protoplasts and the inhibition of this process by compounds that prevent protein or polysaccharide synthesis. The third approach has investigations of the enzymic processes involved in mannan synthesis, using cell-free extracts and following incorporation of radioactive mannose into endogenous and exogenous acceptors. The chapter discusses the detailed structures of specific yeast mannans.

Influence of the rate of ethanol production and accumulation on the viability of Saccharomyces cerevisiae in "rapid fermentation".

Abstract: Whereas "rapid fermentation" of diluted clover honey (25 degrees Brix) fortified with yeast nutrients using 8 X 10(8) brewers' yeast cells per ml resulted in an ethanol content of 9.5% (wt/vol; 12% vol/vol) in 3 h at 30 C, death rate of the yeast cells during this period was essentially logarithmic. Whereas 6 h was required to reach the same ethanol content at 15 C, the yeast cells retained their viability. Using a lower cell population (6 X 10(7) cells/ml), a level at which the fermentation was no longer "rapid," the yeast cells also retained their viability at 30 C. Ethanol added to the medium was much less lethal than the same or less quantities of ethanol produced by the cell in "rapid fermentation." It was considered possible that ethanol was produced so rapidly at 30 C that it could not diffuse out of the cell as rapidly as it was formed. The hypothesis was postulated that ethanol accumulating in the cell was contributing to the high death rate at 30 C. It was found that the intracellular ethanol concentration reached a level of approximately 2 X 10(11) ethanol molecules/cell in the first 30 min of fermentation at 30 C. At 15 C, with the same cell count, intracellular ethanol concentration reached a level of approximately 4 X 10(10) ethanol molecules/cell and viability remained high. Also, at 30 C with a lower cell population (6 X 10(7) cells/ml), under which conditions fermentation was no longer "rapid," intracellular ethanol concentration reached a similar level (4 X 10(10) molecules ethanol/cell) and the cells retained their viability. Alcohol dehydrogenase (ADH) lost its activity in brewers' yeast under conditions of "rapid fermentation" at 30 C but retained its activity in cells under similar conditions at 15 C. ADH activity was also retained in fermentations at 30 C with cell populations of 6 X 10(7)/ml. It would appear that an intracellular level of about 5 X 10(10) ethanol molecules/cell is normal and that this level does not damage either cell viability or ADH activity. Higher intracellular ethanol concentrations, such as 2 X 10(11) molecules ethanol/cell (a fourfold increase in intracellular ethanol concentration), are accompanied by inactivation of ADH and loss of cell viability.

Primary Structure of α‐Factor Peptides from Saccharomyces cerevisiae

Abstract: The amino acid sequences of the mating hormones produced by α-mating-type cells of the yeast Saccharomyces cerevisiae (α factor peptides α1, α2, α3 and α4) have been determined. By cleavage of the peptides with thermolysin and pepsin and structural analysis of the fragments the sequence H2N-Trp-His-Trp-Leu-Gln-Leu-Lys-Pro-Gly-Gln-Pro-Met-Tyr-COOH could be assigned to α1. α2 lacks the N-terminal tryptophan residue. α3 and α4 represent the methionine sulfoxides of α1 and α2 respectively.

Inhibition of phagocytosis by cryptococcal polysaccharide: dissociation of the attachment and ingestion phases of phagocytosis.

Abstract: The effects of cryptococcal polysaccharide and selected serum factors on (i) the attachment of Cryptococcus neoformans to macrophages and (ii) the subsequent ingestion of yeast cells by the macrophages were investigated. Percent attachment was measured after incubation of yeast cells with macrophages at 4 C. Percent engulfment was determined after incubation of yeast cells and macrophages at 37 C. Nonencapsulated yeast cells readily attached to macrophages at the low temperature and were engulfed at a high rate at 37 C, whereas encapsulated yeast cells attached to macrophages at low rates and were engulfed at low rates. Addition of varying doses of purified cryptococcal polysaccharide to nonencapsulated yeast cells inhibited attachment at approximately the same concentration of polysaccharide required for inhibition of engulfment. Nonencapsulated yeast cells that attached to macrophages at 4 C were eluted from the macrophages by addition of purified cryptococcal polysaccharide to the incubation medium. Heat-labile opsonins were not required for attachment of yeast cells to macrophages, but they were necessary for maximal initial rates of phagocytosis. Heat-stable components of serum facilitated attachment of cryptococci, but their most important function appeared to be triggering the ingestion of attached yeast. Specific antiserum had no effect on the attachment and engulfment of nonencapsulated cryptococci, and the antiserum produced only a small enhancement of the engulfment of encapsulated cryptococci.

Thermal adaptation in yeast: growth temperatures, membrane lipid, and cytochrome composition of psychrophilic, mesophilic, and thermophilic yeasts.

Abstract: The temperature limits of growth of a number of yeast species were examined, and on this basis the organisms were classified into different thermal categories. The following species were examined: Leucosporidium frigidum and Leucosporidium nivalis, psychrophilic, temperature limits of growth, -2 to 20 degrees C; Canadian lipolytica mesophilic, temperature limits of growth, 5 to 35 degrees Candida parapsilosis and Saccharomyces telluris, thermotolerant, temperature limits of growth, 8 to 42 degrees C; Torulopsis bovina and Candida slooffi, thermophilic, temperature limits of growth, 25 to 45 degrees C and 28 to 45 degrees C, respectively. The membrane lipid and cytochrome composition of mitochrondrial fractions isolated from these yeasts were compared. There was a direct correlation between the growth temperature and the degree of membrane of lipid unsaturation; the lower the temperature, the greater the degree of lipid unsaturation. The membrane lipid composition of the thermophilic yeasts were distinguished by the high percentage (30 to 40%) of saturated fatty acid, as compared with the mesophilic and psychrophilic yeasts. The latter contained approximately 90% unsaturated fatty acid, 55% of which was linolenic acid, C alpha-18:3. Changes in phospholipid composition in relation to temperature were also noted. The respiratory-deficient thermophile, C. slooffi, was characterized by the absence of cardiolipin (sensitivity 0.1 mug of phosphorus) and cytochrome aa3. The absence of conventional mitochondrial structures in this thermophilic microorganism is tentatively suggested although low concentrations of cytochromes b, c, and c1 were detected by low-temperature spectroscopy. On the other hand, the respiratory-competent thermophile, T. bovina, was characterized by a high cardiolipin (25% of the total phospholipid) and cytochrome aa3 content (1 nmol/mg of mitochrondrial protein). Low-temperature spectra showed the presence of one b-type cytochrome in the thermophilic yeasts, two b-type cytochromes in the mesophilic yeasts, and three b-type cytochromes in the psychrophilic yeasts. It was concluded that a knowledge of the properties of the biological membrane is fundamental to an understanding of the ability of a microorganism to grow and reproduce in different temperature environments.

Organic acid metabolism of yeasts during fermentation of alcoholic beverages—a review

Abstract: The acids of alcoholic beverages are largely those present in the raw materials but the concentrations of some may be changed by yeast action during fermentation. In addition a number of other acids are formed by the yeasts often as by-products of main metabolic pathways. The inter-relationships of organic acid and amino-acid metabolism, yeast growth and formation of fusel alcohols are discussed.

Proteolytic activation and inactivation of chitin synthetase from Mucor rouxii.

Abstract: Summary: Crude chitin synthetase preparations from the mycelial and yeast forms of Mucor rouxii behaved differently. The mycelial preparations, incubated at 28 °C, lost virtually all chitin synthetase activity in a few hours; by contrast, the activity of enzyme preparations from yeast cells increased several fold during similar incubations. These spontaneous changes were probably caused by endogenous protease(s). Seemingly, the chitin synthetase in yeast preparations was present mainly in a latent, ‘zymogenic’, form that was activated by proteases. In the mycelial preparations, chitin synthetase was present mainly in an active state and was rapidly degraded by endogenous proteolysis. Exogenous proteases accelerated activation and destruction of chitin synthetase; an acid protease from Rhizopus chinensis was the most effective activator. The activation of chitin synthetase was inhibited by a soluble protein in the cell-free extract. Treatment with the detergent Brij 36T stabilized the chitin synthetase of crude preparations against spontaneous changes. Stabilized preparations were rapidly activated by exogenous proteases. The different behaviour of chitin synthetases in crude extracts of mycelium and yeast cells is consistent with, and perhaps partially responsible for, the differences in wall construction between mycelial and yeast forms of M. rouxii.

Lipid composition of 30 species of yeast.

Abstract: The detailed composition of cellular lipid of more than 23 species of yeast has been determined quantitatively by thinchrography on quartz rods, a method previously used for estimating cellular lipids of seven species of yeast. That data was fortified by neutral and phospholipid quantitations on 30 species of yeast cells. Most of the test organisms contained 7-15% total lipid and 3-6% total phospholipid per dry cell weight, except for the extremely high accumulation of triglycerides in two species of Lipomyces. Qualitatively, 30 species of yeast cells contained similar neutral lipid constituents (triglyceride, sterol ester, free fatty acid, and free sterol) and polar lipid components (phosphatidyl choline, phosphatidyl ehtanolamine, phosphatidyl serine, phosphatidyl inositol, cardiolipin, and ceramide monohexoside) without minor constituents. Based on the quantitative composition of neutral lipids, the 30 species of yeast were divided into two groups , the triglyceride predominant group and the sterol derivative group. These groupings were fairly well overlapped from the standpoint of the distribution characteristics of fatty acid. The relative polar lipid compositions also grossly resembled each other. Only one exception of polar lipid composition in yeast cells was found in Rhodotorula rubra species which contained phosphatidyl ethanolamine as the most abundant phospholipid. Fatty acid distribution patterns in yeast cells consistently coincided with other reports concerning fatty acid composition of yeast cells. Correlation of lipid composition and classification of yeasts are suggested and discussed.

The Production and Growth Characteristics of Yeast and Mycelial Forms of Candida albicans in Continuous Culture

Abstract: SUMMARY: The growth characteristics of Candida albicans CM145,348 have been examined under aerobic conditions in continuous culture. At different steady states the environment was controlled with respect to the concentrations of dissolved oxygen, carbon and nitrogen, the pH, and the temperature. Dry matter, substrate concentration, yield, specific oxygen uptake, specific carbon dioxide release and respiration quotient were examined as a function of the dilution rate. The morphology depended on the carbon source. Maltose produced a mycelial morphology, whereas with lactate a yeast culture was obtained. With fructose or glucose as a carbon source a mixed morphology of yeast, pseudo-mycelial and mycelial forms was produced. A large number of different growth conditions were examined in batch culture but a mixed morphology was always obtained.

Growth of nitrobacter in the presence of organic matter. II. Chemoorganotrophic growth of Nitrobacter agilis.

Abstract: 1. After a resting period of up to 6 months cells of Nitrobacter agilis grow with acetate, formate, and pyruvate as carbon and energy source. Yeast extract and peptone were added to supply the organism with nitrogen and to meet possible vitamin requirements. 2. The length of the growth period depends on the substrate; it increases according to the following sequence: pyruvate, formate, acetate. The highest growth yield is observed with pyruvate, the lowest with formate. 3. O2 consumption is increased in the presence of substrates as compared to endogenous respiration. With pyruvate and acetate twice as much O2 is consumed, with formate 7 times, with yeast extractpeptone 10 times as much. 4. The ability of nitrite oxidation is largely preserved, except in cells grown with acetate or pyruvate in the presence of 0.015% yeast extract and peptone. Such cells have nearly no cytochrome a1. Accordingly. the cytochrome spectra of nitrite oxidizers grown under chemoorganotrophic and lithoautotrophic conditions coincide qualitatively. 5. The nitrite oxidizing system is inducible. It is induced by nitrite but also by substances present in yeast extract and peptone. Cells grown on acetate and yeast extract and peptone (0.015%) require 3--4 weeks before they regain the ability to grow with nitrite. Cells grown chemoorganotrophically with the same substrates and yeast extract and peptone (0.15%) start growing and nitrite as energy source without a lag. 6. Cell size and form, distribution of storage materials, order and fine structure of double membranes are correlated with growth conditions.

Mechanism of Discrimination between Cognate and Non‐cognate tRNs by Phenylalanyl‐tRNA:Synthetase from Yeast

Abstract: The interaction between phenylalanyl-tRNA synthetase from yeast and Escherichia coli and tRNAPhe (yeast), tRNASer (yeast), tRNA1Val (E. coli) has been investigated by ultracentrifugation analysis, fluorescence titrations and fast kinetic techniques. The fluorescence of the Y-base of tRNAPhe and the intrinsic fluorescence of the synthetases have been used as optical indicators. 1. Specific complexes between phenylalanyl-tRNA synthetase and tRNAPhe from yeast are formed in a two-step mechanism: a nearly diffusion-controlled recombination is followed by a fast conformational transition. Binding constants, rate constants and changes in the quantum yield of the Y-base fluorescence upon binding are given under a variety of conditions with respect to pH, added salt, concentration of Mg2+ ions and temperature. 2. Heterologous complexes between phenylalanyl-tRNA synthetase (E. coli) and tRNAPhe (yeast) are formed in a similar two-step mechanism as the specific complexes; the conformational transition, however, is slower by a factor 4-5. 3. Formation of non-specific complexes between phenylalanyl-tRNA synthetase (yeast) and tRNATyr (E. coli) proceeds in a one-step mechanism. Phenylalanyl-tRNA synthetase (yeast) binds either two molecules of tRNAPhe (yeast) or only one molecule of tRNATyr (E. coli); tRNA1Val (E. coli) or tRNASer (yeast) are also bound in a 1:1 stoichiometry. Binding constants for complexes of phenylalanyl-tRNA synthetase (yeast) and tRNATyr (E. coli) are determined under a variety of conditions. In contrast to specific complex formation, non-specific binding is disfavoured by the presence of Mg2+ ions, and is not affected by pH and the presence of pyrophosphate. The difference in the stabilities of specific and non-specific complexes can be varied by a factor of 2--100 depending on the ionic conditions. Discrimination of cognate and non-cognate tRNA by phenylalanyl-tRNA synthetase (yeast) is discussed in terms of the binding mechanism, the topology of the binding sites, the nature of interacting forces and the relation between specificity and ionic conditions.

Mutagenicity of atrazine: A maize-microbe bioassay

Abstract: A water-soluble extract from maize plants grown in the presence of atrazine contained a mutagenic agent(s) when tested on strains of yeast. Atrazine alone or control plants not treated with atrazine did not express mutagenic properties. The reversion frequency at the waxy locus in pollen grains from plants grown in atrazine was higher than in control plants. We suggest that atrazine may be degraded by the plant into environmental mutagenic agents.

Isolation of carboxypeptidase Y by affinity chromatography

Abstract: Carboxypeptidase Y from bakers’ yeast has been purified in high yields by affinity chromatography. The affinity gel was prepared by coupling the specific inhibitor p-aminobenzylsuccinic acid via an azo linkage to Sepharoseglycyl-tyrosine. This affinity gel was able to bind carboxypeptidase Y specifically and quantitatively from a crude yeast autolysate. The isolated enzyme appeared homogeneous by gel electrophoresis and ultracentrifugation, while isoelectric focusing revealed the presence of two components with isoelectric points of pH 3.56 and 3.66, respectively. Small differences in amino acid composition and enzymatic properties between the enzyme from danish yeast and the corresponding enzyme isolated from Fleichmann yeast suggested the existence of more than one form of this enzyme.

Environmental determination of selective significance or neutrality of amylase variants in drosophila melanogaster

Abstract: Strains homozygous at the amylase locus were derived from a polymorphic laboratory population of Drosophila melanogaster . The Amy 4,6 strain has higher enzyme activity than the Amy 1 strain.—Maltose has the same nutritional value as starch.—The effect of starch in pure culture depends on the yeast level. At low yeast level increasing starch increases survival, at high yeast level increasing starch increases mean dry weight. The strains do not differ in survival or mean dry weight in pure culture.—In mixed cultures at 50% input of Amy 4,6 and Amy 1 as larvae the percentage Amy 4,6 in adults increases with increasing starch at low yeast levels, but equals input frequency at high yeast levels. No increase in percentage Amy 4,6 in adults is present with increasing maltose at low yeast levels in mixed culture. The increase in percentage Amy 4,6 with increasing starch must be due to selection on the amylase locus working by competition for food in the larval stage. The single locus selection coefficient is determined by the environment and can reach quite high values.—Viability selection in the presence of starch is in the direction indicated by the enzyme activities.

Carbon dioxide inhibition of yeast growth in biomass production

Abstract: Saccharomyces cerevisiae was grown under aerobic and substrate-limiting conditions for efficient biomass production. Under these conditions, where the sugar substrate was fed incrementally, the growth pattern of the yeast cells was found to be uniform, as indicated by a constant respiratory quotient during the entire growing period. The effect of carbon dioxide was investigated by replacing portions of the nitrogen in the air stream with carbon dioxide, while maintaining the oxygen content at the normal 20% level, so that identical oxygen transfer rate and atmospheric pressure were maintained for all experiments with different partial pressures of carbon dioxide. Inhibition of yeast growth was negligible below 20% CO2 in the aeration mixture. Slight inhibition was noted at the 40% CO2 level and significant inhibition was noted above the 50% CO2 level, corresponding to 1.6 X 10(-2)M of dissolved CO2 in the fermentor broth. High carbon dioxide content in the gas phase also inhibited the fermentation activity of baker's yeast.

The effects of “Cell age” upon the lethal effects of physical and chemical mutagens in the yeast, Saccharomyces cerevisiae

Abstract: Summary Yeast cultures progressing from the exponential to the stationary phase of growth showed changes in cell sensitivity to physical agents such as UV light, heat shock at 52° C and the chemical mutagens ethyl methane sulphonate, nitrous acid and mitomycin C. Exponential phase cells showed maximum resistance to UV light and minimum resistance to heat shock and the three chemicals. The increased resistance of exponential phase cells to UV light was shown to be dependent upon the functional integrity of the RAD 50 gene. Treatment of growing yeast cultures with radioactively labelled ethyl methane sulphonate indicated the preferential uptake of radioactivity during the sensitive exponential stage of growth. The results indicated that the differential uptake of the chemical mutagens was responsible for at least a fraction of the variations in cell sensitivity observed in yeast cultures at different phases of growth.

FACTORS RESPONSIBLE FOR THE DECREASE IN pH DURING BEER FERMENTATIONS

Abstract: The relative significance of factors which cause pH to decrease during fermentation has been investigated, using eleven yeast strains. Organic acid excretion and absorption of basic amino acids both have substantial effects: solution of carbon dioxide and absorption of primary phosphate contribute to a small extent. Buffering capacity, over the pH range 4 to 5, increases slightly during fermentation. Approximately 30% of the increase in hydrogen ion concentration cannot be attributed to known causes; direct excretion of hydrogen ions may be responsible. Fermentation with yeast propagated in semi-aerobic conditions rather than in fermentors gives beers of lower pH and increased organic acid content, but the latter factor is not in itself sufficient to account for the pH difference.

Heat Resistance Studies on Yeast spp. Causing Spoilage in Soft Drinks

Abstract: A test method to investigate the heat resistance of yeasts has been developed The method was used to study the heat resistance of 120 yeast strains, representative of the fungal flora in soft drinks and certain acid food products: 35 asporogenous yeast strains (Brettanomyces, Candida, Kloeckera, Rhodotorula and Torulopsis) and 85 ascomycetous strains (Debaryomyces, Hansenula, Kluyveromyces, Lodderomyces, Pichia, Saccharomyces and Saccharomycopsis) were tested Generally, asporogenous yeasts were found to be less heat resistant than ascomycetous types The genus Saccharomyces showed the highest heat resistance, especially strains of the species Sacch cerevisiae and Sacch chevalieri For an evaluation of the practical implications of these results additional studies on environmental factors influencing the heat resistance of ascomycetous yeast species are required

The transport of S-adenosyl-L-methionine in isolated yeast vacuoles and spheroplasts.

Abstract: 1 The properties of S-adenosyl-l-methionine accumulating system for both vacuoles and spheroplasts are described. Yeast vacuoles were obtained by a modified metabolic lysis procedure from spheroplasts of Saccharomyces cerevisiae. 2 Isolated vacuoles accumulate S-adenosyl-l-methionine by means of a highly specific transport system as indicated by competition experiments with sitructural analogs of S-adenosyl-lm-methionine. The S-adenosyl-l-methionine transport system shows saturation kinetics with an apparent Km of 68 μM in vacuoles and 11 μM in spheroplasts. 3 S-Adenosyl-l-methionine accumulation into vacuoles does not require glucose, phosphoeno/pyruvic acid, ATP, ADP nor any other tri- or di-phosphorylated nucleotides. It is insensitive to azide and 2,4-dinitrophenol which strongly inhibit the glucose-dependent accumulation of Sadenosyl-l-methionine in spheroplasts. 4 The transport of S-adenosyl-l-methionine into vacuoles is optimal at pH 7.4 and is insensitive to nystatin while the uptake of S-adenosyl-l-methionine into spheroplasts is optimal at pH 5.0 and is strongly sensitive to nystatin. On this basis it has thus been possible to measure both the intracytoplasmic and the intravacuolar pool of S-adenosyl-l-methionine. 5 Our results indicate the existence of a highly specific S-adenosyl-l-methionine transport system in the vacuolar membrane which is clearly different from the one present in the plasma membrane of yeast cells.