Endogenous respiration of yeast. I. The endogenous substrate

Lumping kinetics of ABE fermentation wastewater treatment by oleaginous yeast Trichosporon cutaneum

Lumping kinetics models were built for the biological treatment of acetone-butanol-ethanol (ABE) fermentation wastewater by oleaginous yeast Trichosporon cutaneum with different fermentation temperatures. Compared with high temperature (33°C, 306 K) and low temperature (23°C, 296 K), medium temperature (28°C, 301 K) was beneficial for the cell growth and chemical oxygen demand (COD) degradation during the early stage of fermentation but the final yeast biomass and COD removal were influenced little. By lumping method, the materials in the bioconversion network were divided into five lumps (COD, lipid, polysaccharide, other intracellular products, other extracellular products), and the nine rate constants (k₁-k₉) for the models can well explain the bioconversion laws. The Gibbs free energy (G) for this bioconversion was positive, showing that it cannot happen spontaneous, but the existence of yeast can after the chemical equilibrium and make the bioconversion to be possible. Overall, the possibility of using lumping kinetics for elucidating the laws of materials conversion in the biological treatment of ABE fermentation wastewater by T. cutaneum has been initially proved and this method has great potential for further application.

Yeast responses to stresses associated with industrial brewery handling: Figure 1

During brewery handling, production strains of yeast must respond to fluctuations in dissolved oxygen concentration, pH, osmolarity, ethanol concentration, nutrient supply and temperature. Fermentation performance of brewing yeast strains is dependent on their ability to adapt to these changes, particularly during batch brewery fermentation which involves the recycling (repitching) of a single yeast culture (slurry) over a number of fermentations (generations). Modern practices, such as the use of high-gravity worts and preparation of dried yeast for use as an inoculum, have increased the magnitude of the stresses to which the cell is subjected. The ability of yeast to respond effectively to these conditions is essential not only for beer production but also for maintaining the fermentation fitness of yeast for use in subsequent fermentations. During brewery handling, cells inhabit a complex environment and our understanding of stress responses under such conditions is limited. The advent of techniques capable of determining genomic and proteomic changes within the cell is likely vastly to improve our knowledge of yeast stress responses during industrial brewery handling.

Specific features of changes in levels of endogenous respiration substrates in Saccharomyces cerevisiae cells at low temperature

The rate of endogenous respiration of Saccharomyces cerevisiae cells incubated at 0 degrees C under aerobic conditions in the absence of exogenous substrates decreased exponentially with a half-period of about 5 h when measured at 30 degrees C. This was associated with an indirectly shown decrease in the level of oxaloacetate in the mitochondria in situ. The initial concentration of oxaloacetate significantly decreased the activity of succinate dehydrogenase. The rate of cell respiration in the presence of acetate and other exogenous substrates producing acetyl-CoA in mitochondria also decreased, whereas the respiration rate on succinate increased. These changes were accompanied by an at least threefold increase in the L-malate concentration in the cells within 24 h. It is suggested that the increase in the L-malate level in the cells and the concurrent decrease in the oxaloacetate level in the mitochondria should be associated with a deceleration at 0 degrees C of the transport of endogenous respiration substrates from the cytosol into the mitochondria. This deceleration is likely to be caused by a high Arrhenius activation energy specific for transporters. The physiological significance of L-malate in regulation of the S. cerevisiae cell respiration is discussed.

METABOLISM OF INTRACELLULAR POLYSACCHARIDE BY STREPTOCOCCUS MITIS AND ITS RELATION TO INDUCIBLE ENZYME FORMATION

Gibbons, R. J. (Forsyth Dental Center, Boston Mass.). Metabolism of intracellular polysaccharide by Streptococcus mitis and its relation to inducible enzyme formation. J. Bacteriol. 87:1512-1520. 1964.-The synthesis and catabolism of an intracellular iodine staining polysaccharide produced from glucose by Streptococcus mitis was investigated. Approximately 15% of the total glucose metabolized by buffered suspensions of S. mitis was assimilated. Over 90% of the assimilated glucose was converted into a polysaccharide of the glycogen-amylopectin type. Use of uniformly labeled C(14)-glucose provided a convenient method for determining polysaccharide accumulation in this organism. Glucose assimilation occurred at a rate of over 80 mug of glucose per hr per 100 mug of starting dry cell weight. Prolonged assimilation produced cells containing over 50% polysaccharide on a dry weight basis. Accumulated polysaccharide was catabolized at the same rate when the organism was suspended in buffer, sugar-free broth, or sugar-free broth containing thiomethyl galactoside. Metabolic intermediates produced from polysaccharide catabolism did not markedly repress inducible enzyme synthesis. The last glucose molecules incorporated into polysaccharide were among the first molecules to be removed during catabolism. Catabolism of polysaccharide provides S. mitis with energy in a utilizable form, for cells containing polysaccharide increased in beta-galactosidase activity when induced with thiomethyl galactoside in the absence of an exogenous energy source. Cells devoid of polysaccharide, and a polysaccharide-negative variant of S. mitis did not increase in beta-galactosidase activity when induced in a similar manner. It appears that the intracellular polysaccharide is the sole substrate for the endogenous metabolism of S. mitis.

Reserve carbohydrate metabolism in Saccharomyces cerevisiae: responses to nutrient limitation

The amounts of glycogen and trehalose have been measured in cells of a prototrophic diploid yeast strain subjected to a variety of nutrient limitations. Both glycogen and trehalose were accumulated in cells deprived specifically of nirogen, sulfur, or phosphorus, suggesting that reserve carbohydrate accumulation is a general response to nutrient limitation. The patterns of accumulation and utilization of glycogen and trehalose were not identical under these conditions, suggesting that the two carbohydrates may play distinct physiological roles. Glycogen and trehalose were also accumulated by cells undergoing carbon and energy limitation, both during diauxic growth in a relatively poor medium and during the approach to stationary phase in a rich medium. Growth in the rich medium was shown to be carbon or energy limited or both, although the interaction between carbon source limitation and oxygen limitation was complex. In both media, the pattern of glycogen accumulation and utilization was compatible with its serving as a source of energy both during respiratory adaptation and during a subsequent starvation. In contrast, the pattern of trehalose accumulation and utilization seemed compatible only with the latter role. In cultures that were depleting their supplies of exogenous glucose, the accumulation of glycogen began at glucose concentrations well above those sufficient to suppress glycogen accumulation in cultures growing with a constant concentration of exogenous glucose. The mechanism of this effect is not clear, but may involve a response to the rapid rate of change in the glucose concentration.

Effect of tryptophan on growth and morphology of Hansenula schneggii cells

Sundhagul, Malee (Illinois Institute of Technology, Chicago), and L. R. Hedrick. Effect of tryptophan on growth and morphology of Hansenula schneggii cells. J. Bacteriol. 92:241-249. 1966.-When Hansenula schneggii cells were cultured aerobically in a tryptophan-glucose medium, 70 to 90% of the cells were elongated; no growth occurred under anaerobic conditions. The size of the elongated cells was 15 to 25 mu by 2 to 4 mu, as compared with 2.5 to 5 mu for ellipsoidal cells. Formation of elongated cells occurred essentially during the logarithmic growth period; the highest percentage of elongated cells was found soon after the end of this growth phase. In the later stationary phase, some of the cells formed spherical buds which became spherical cells. The rate of cell division during this period was greatly reduced, but the spherical cells formed decreased the percentage of elongated cells in the population. Cells cultured in a membrane-filter filtrate of a tryptophan-glucose medium (with limiting tryptophan), in which elongated cells had been grown, were ellipsoidal until nitrogenous nutrients were exhausted; thereafter the cells were elongated if tryptophan was added. Of compounds related to tryptophan, kynurenine was the only one which induced a high percentage of the cells to elongate. Some amino acids, such as cystine, histidine, phenylalanine, tyrosine, and threonine, induced elongation in about 15% of the cells. Growth of cells with other amino acids, or the addition of most of the other amino acids to tryptophan-glucose medium, resulted in a population of spherical cells. Several consecutive sequential transfers of cells into tryptophan medium induced elongation in 90% of the cells, but one transfer from a culture with elongated cells into a medium with ammonium sulfate, or a mixture of amino acids, gave a culture with ellipsoidal cells. Growth in media at pH 4 or 5 favored formation of elongated cells; as the pH was increased, the percentage of elongated cells decreased. Carbon sources other than glucose did not affect the percentage of elongated cells, except for the alcohols mannitol and erythitol, which gave comparable growth but reduced the percentage of elongated cells from 70 to 50%. Cell wall analyses of the two types of cells indicated that elongated cells have 2.5 times as much mannan as cell walls of ellipsoidal cells. This suggests that tryptophan, kynurenine, and, to a limited extent, some of the other amino acids cause a diversion of polysaccharide biosynthesis to mannan in the elongated cells rather than to glucan as in ellipsoidal cells.

THE METABOLISM OF YEAST SPORULATION: IV. CYTOLOGICAL AND PHYSIOLOGICAL CHANGES IN SPORULATING CELLS

Parallel observations were made of respiratory activity, content of glycogen and fat, and appearance of the nucleus, during transition of cells of Saccharomyces cerevisiae from the vegetative to the sporulated state. With acetate as the carbon source in sporulation medium, the endogenous respiratory ability of the cells first increased (after about 10 hours) and finally declined. Ability to respire glucose remained high during sporogenesis but diminished somewhat by 42–43 hours, at which time most of the cells contained spores. Glycogen and fat increased in amount during the early stages of sporogenesis but appeared to diminish during formation of spore walls. In vegetative and reductional nuclear division the nuclear material appeared organized into rod-like structures, some regions of which stained more densely. Classical cytological configurations were not observed. With dihydroxyacetone as the carbon source in sporulation medium the sequence of events was similar, but required about twice as much time, possibly owing to the slower respiration of this substance.

ENDOGENOUS RESPIRATION OF STAPHYLOCOCCUS AUREUS

Ramsey , H. H. (Stanford University, Palo Alto, Calif.). Endogenous respiration of Staphylococcus aureus . J. Bacteriol. 83: 507–514. 1962.—The endogenous respiration of Staphylococcus aureus is dependent upon the medium used to grow the cell suspension. Within wide ranges, the concentration of glucose in the medium has no effect upon subsequent endogenous respiration of the cells, but the concentration of amino acids in the medium, within certain limits, has a very marked effect. The total carbohydrate content of the cells does not decrease during endogenous respiration. As endogenous respiration proceeds, ammonia appears in the supernatant, and the concentration of glutamic acid in the free amino acid pool decreases. Organisms grown in the presence of labeled glutamic acid liberate labeled CO 2 when allowed to respire without added substrate. The principal source of this CO 2 is the free glutamate in the metabolic pool; its liberation is not suppressed by exogenous glucose or glutamate. With totally labeled cells, the free pool undergoes a rapid, but not total, depletion and remains at a low level for a long time. Activity of the protein fraction declines with time and shows the largest net decrease of all fractions. Exogenous glucose does not inhibit the release of labeled CO 2 by totally labeled cells. Other amino acids in the free pool which can serve as endogenous substrates are aspartic acid and, to much lesser extents, glycine and alanine. The results indicate that both free amino acids and cellular protein may serve as endogenous substrates of S. aureus .