Response of the adenosine phosphate pool level to changes in the catabolic pattern of Saccharomyces cerevisiae

Fermentation of corn starch to ethanol with genetically engineered yeast

Expression of the glucoamylase gene from Aspergillus awamori by laboratory and distiller's strains of Saccharomyces cerevisiae allowed them to ferment soluble starch. Approximately 95% of the carbohydrates in the starch were utilized. Glycerol production was significantly decreased when soluble starch was used instead of glucose. Ethanol yield on soluble starch was higher than that on glucose. The rate of starch fermentation was directly related to the level of glucoamylase activity. Strains with higher levels of glucoamylase expression fermented starch faster. The decline in starch fermentation rates toward the end of the fermentation was associated with accumulation of disaccharides and limit dextrins, poor substrates for glucoamylase. The buildup of these products in continuous fermentations inhibited glucoamylase activity and complete utilization of the starch. Under these conditions maltose-fermenting strains had a significant advantage over nonfermenting strains. The synthesis and secretion of glucoamylase showed no deleterious effects on cell growth rates, fermetation rates, and fermentation products.

Glucose starvation induces a drastic reduction in the rates of both transcription and degradation of mRNA in yeast

Gradual depletion of essential nutrients in yeast cultures induces a complex physiological response, leading initially to induction of pathways required for the utilization of alternative nutrients and, when such sources are depleted, to entry into stationary phase. Abrupt removal of sugar does not allow the proper establishment of stationary phase. Here we report that abrupt removal of glucose from the growth medium elicits a coordinated response in yeast cells that resembles, in some aspects, the gradual passage to stationary phase. Phosphorylation of RNA polymerase II at a subset of sites in the COOH-terminal domain (CTD) is decreased. Transcription by RNA polymerases I and II is shut down almost completely, whereas transcription by RNA polymerase III continues. In parallel, the rate of mRNA degradation is drastically reduced, at a stage preceding poly(A) shortening. This response is suited for conservation of scarce resources while preserving the ability of cells to recover when nutrients become available.

Rapid and highly automated determination of adenine and pyridine nucleotides in extracts of Saccharomyces cerevisiae using a micro robotic sample preparation-HPLC system

An ion-pair reversed-phase chromatography method was adapted for the simultaneous separation and quantification of adenine and pyridine nucleotide concentrations in cell extracts of Saccharomyces cerevisiae. Microbial extracts including metabolites, macromolecular constituents and inorganic compounds were loaded onto a ODS pre-column in the presence of triethylamine phosphate (TEA-Pi) resulting in a selective binding of the nucleotides and removing of interfering compounds. After washing the enrichment cartridge with 30 mM TEA-Pi buffer, adenine and pyridine nucleotides were eluted with a gradient of Mg(II), the competing hetaeron. This combined cleaning and concentration step leads to remarkable improvement of the detection limit for all nucleotides of interest and column lifetimes. The clean up and separation procedures were performed automatically with a micro robotic-system and a control software package written in PASCAL. The paper reports about the application of the proposed method to separation of adenine and pyridine nucleotides in cells extracts of S. cerevisiae grown anaerobically in a continuous culture (D = 0.1 h-1). Rapidity of analysis, high sensitivity as well as reproducibility of the system and the accurate evaluation of the adenine and pyridine nucleotide concentrations make this method particularly useful for routine analysis.

Growth characteristics of Candida utilis on volatile substrate in a multistage tower fermentor

The influence of increasing ethanol concentration in the feed on growth and physiological activity of the yeast Candida utlis was studied. The measurements were made at steady states of continuous culture under constant values of dilution rate, temperature, and pH in all stages of the fermentor; Synthetic ethanol was used as the sole source of carbon and energy in the concentration range 10-100 g/liter. The maximum biomass concentration in the effluent and maximum productivity was achieved at 75 g ethanol/liter in the feed. In respect to ethanol losses in the outlet and biomass yield, the optimum ethanol concentration in the input of the growth medium was found to be about 50 g/liter using a four-stage system.

Utilization of cellulosic materials through enzyamtic hydrolysis. I. Fermentation of hydrolysate to ethanol and single-cell protein

Ethanol fermentation studies were conducted with Saccharomyces cerevisiae ATCC "4126, to determine the optimal conditions of oxygen tension and feed sugar concentration. In long-term continuous culture maximum ethanol production was found to occur at 0.07 mmHg oxygen tension and 10% glucose feed concentration. Preliminary process design and cost studies are developed for industrial scale fermentations to produce ethanol and torula yeast from sugars obtained by enzymatic hydrolysis of newsprint.