Kinetics of asparaginase II fermentation in Saccharomyces cerevisiae ure2dal80 mutant

Although the quality of nitrogen source affects fermentation product formation, it has been managed empirically, to a large extent, in industrial scale. Laboratory-scale experiments successfully use the high-cost proline as a nonrepressive source. We evaluated urea as a substitute for proline in Saccharomyces cerevisiae ure2dal80 fermentations for asparaginase II production as a model system for nitrogen-regulated external enzymes. Maximum asparaginase II levels of 265 IU/L were observed in early stationary-phase cells grown on either proline or urea, whereas in ammonium cells, the maximum enzyme level was 157 IU/L. In all cases, enzyme stability was higher in buffered cultures with an initial pH of 6.5.     

IMMOBILIZATION OF Saccharomyces Cerevisiae USING POLY（ACRYLAMIDE） GEL FOR ASYMMETRIC SYNTHESIS OF R（-）-MANDELIC ACID

In this paper, the poly(acrylamide) hydrogel used to immobilize saccharomyces cerevisiae for asymmetric synthesis of R(-)-mandelic acid was prepared with free radical ploymerization in deionized water at room temperature under nitrogen atmosphere. The influence of the composition of hydrogel, loading amount of cells and culture conditions on the asymmetric synthesis was investigated. Results show that PAAm hydrogel is a feasible carrier for immobilization of cells which is a potential alternative method to prepare enantiomerically pure R(-)-mandelic acid.     

Trace enrichment of metal ions in aquatic environments by Saccharomyces cerevisiae

Sorption properties of baker’s yeast cells, characterised as Saccharomyces cerevisiae were evaluated for trace enrichment of metal ions: Cd²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Pb²⁺ and Zn²⁺ from aqueous environments. Metal concentration was determined by flame atomic absorption spectrometry (FAAS). Parameters affecting metal uptake such as solution pH, incubation time, amount of yeast biomass and effect of glucose concentration (energy source) were optimised. Further studies were carried out to evaluate the effects on metal uptake after treating yeast with glucose as well as with an organic solvent. The results showed that trace enrichment of the metals under study with yeast, depends upon the amount of yeast biomass, pH and incubation time. Treatment of yeast cells with 10-20 mM glucose concentration enhanced metal uptake with exception to Cr⁶⁺, whose metal enrichment capacity decreased at glucose concentration of 60 mM. Of the investigated organic solvents THF and DMSO showed the highest and lowest capacity, respectively, to enhance metal uptake by yeast cells. Trace enrichment of metal ions from stream water, dam water, treated wastewater from a sewage plant and wastewater from an electroplating plant achieved enrichment factors (EF) varying from 1 to 98, without pre-treatment of the sample. pH adjustment further enhanced the EF for all samples. The results from these studies demonstrate that yeast is a viable trace metal enrichment media that can be used freely suspended in solution to achieve very high EF in aquatic environments.     

Bioassay-directed chemical analysis utilizing LC–MS: a tool for identifying estrogenic compounds in water samples?

A bioassay-directed chemical analysis (BDCA) scheme has been developed which combines a yeast screen for estrogenic activity with LC–MS detection after liquid–liquid extraction and fractionation by size exclusion chromatography. Focusing on sewage-treatment plant (STP) effluents, the approach aims at characterizing the substances responsible for estrogenic effects in aquatic systems. Initial results show a strong response of STP effluent extracts in the yeast screen. Estrone, bisphenol A, and nonylphenol have been identified as substances being partly responsible for observed estrogenic activity. However, confirmation experiments with synthetic samples revealed that the estrogenic effect potentials of the samples could not be completely assigned to specific compounds. Further improvement of the limits of detection of the analytical scheme is needed to enable identification and quantification of potent estrogenic compounds at low concentrations.     

Mild Pfitzner—Moffat oxidation of the (1→3)-β-D-glucan from Saccharomyces cerevisiae

The structure of the cell wall glucan isolated from the industrial strain of Saccharomyces cerevisiae was characterized as to be composed of a linear (1→3)-β-D-glucan chain with single β-D-glucopyranosyl residues attached to every ninth backbone unit by (1→6)-glycosidic linkages. Mild oxidation of this β-D-glucan with a dimethyl sulfoxide—acetic anhydride reagent yielded an “oxidized” glucan with aldehyde groups introduced at C-6 and carbonyl oxygens located at C-2 and C-4 of the glucopyranosyl rings. The conversion of the oxidized glucan into the polyoxime was used to study the progress of oxidation and to establish the carbonyl groups distribution in this new reactive polysaccharide derived from baker’s yeast cell wall.     

THE THEORY AND PRACTICE OF INSTAN-TANEOUS SPECIFIC GROWTH RATE DEPENDENT FED-BATCH REGIME FOR BAKER''''S YEAST CULTURE

The fed-batch method for baker's yeast culture is fundamental for compressed and activedry yeast making. As a technical know-how it has not been published hitherto. The pub-lication of our own fed-batch regime, in principle and in practice, may serve the biologistsas well as engineers to get better results in microbial production.     

The early stages of Saccharomyces cerevisiae yeast suspensions damage in moderate pulsed electric fields

The objectives of this study were to investigate the effects of pulsed electric fields (PEF) application to colloidal suspension of Saccharomyces cerevisiae. The electrical conductivity measurements during the PEF-treatment of S. cerevisiae suspensions were used to monitor the extent of cell damages in the intervals of electric field strength E = 3–15 kV/cm and time of PEF treatment t_PEF = 10⁻⁴ to 1 s. At relatively small fields (E < 7.5 kV/cm) the early stages of yeast cells damages were observed. At such treatment conditions, the damage was incomplete and developed at long time of PEF treatment, below the value of E = 7.5 kV/cm which is commonly referred in literature as a threshold for this culture. Data obtained for the disintegration in conductivity experiments were found in good correlation with direct counting of yeast lethality using light microscopy. The PEF-induced lethality of the yeast cells and size flocs increased with the mixing of suspensions and the increase of temperature.     

Ethanol production usingZymomonas mobilis in a cross-linked immobilized cell reactor

The bacteriumZymomonas mobilis may be utilized to produce ethanol from glucose in a cross-linked immobilized cell reactor. Reactor startup is much more rapid with cross-linkedZymomonas than with the yeastSaccharomyces cerevisiae. Volumetric ethanol productivities (based on liquid holdup) three times those obtained with cross-linked yeast, and comparable to those obtained withZymomonas immobilized by other methods, are possible.     

Preconcentration of phthalic acid esters in water samples by Saccharomyces cerevisiae immobilized on silica gel

A sensitive and selective column adsorption method is proposed for the off-line preconcentration and determination of phthalic acid esters (PAEs), namely benzyl-butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di-cyclohexyl phthalate (DCHP). The PAEs was preconcentrated on Saccharomyces cerevisiae immobilized on silica gel and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analytes were investigated. Recoveries of BBP, DBP and DCHP were 100±2, 98±2 and 98±3%, respectively, at 95% confidence level under optimum conditions. The detection limits (3S/N) of BBP, DBP and DCHP were 3.2, 6.3 and 3.1 μg l⁻¹, respectively. The capacity of the adsorbent was also examined and found to be 1.4 mg g⁻¹ for BBP and DBP, and 3.6 mg g⁻¹ for DCHP. S. cerevisiae immobilized on silica gel is suitable for repeated use without decreasing recovery up to about 25 adsorption-elution cycles. The proposed method was successfully applied to the determination of PAEs in river water with high precision and accuracy.     

Effect of high voltage electrical discharges on filtration properties of Saccharomyces cerevisiae yeast suspensions

In the present work the dead-end filtration of Saccharomyces cerevisiae yeast suspensions disrupted by high voltage electrical discharges (HVED treatment) was investigated. The efficiency of disruption was evaluated using conductivity disintegration index of suspension Z (Z = 0–1) and absorbance spectra of supernatant solutions. The electronic microscopy study, particle sizing and measuring of ζ-potential and turbidity were used to characterize variation of the colloidal properties of a yeast suspension during disruption. The HVED treatment was found to cause an effective disruption of yeast cells and extraction of intracellular proteins and other bio-products. The study of filtration revealed suspension filterability deterioration after disruption. It was shown that filtration behaviour of the HVED-processed suspensions was governed by cake formation, the filtrate volume decreased and the cake resistance increased with increase of Z. For high levels of disruption (Z > 0.99), filtration was governed by membrane fouling. The optimal dosage of polycationic flocculant promoted the formation of flocks and accelerated filtration. However, selected flocculant (poly(diallyldimethylammonium chloride)) provoked binding of bio-product and was inappropriate for using as an agent enhancing extraction from disrupted yeast cells.