Cadmium biosorption by Saccharomyces cerevisiae

Cadmium uptake by nonliving and resting cells of Saccharomyces cerevisiae obtained from aerobic or anaerobic cultures from pure cadmium-bearing solutions was examined. The highest cadmium uptake exceeding 70 mg Cd/g was observed with aerobic baker's yeast biomass from the exponential growth phase. Nearly linear sorption isotherms featured by higher sorbing resting cells together with metal deposits localized exclusively in vacuoles indicate the possibility of a different metal-sequestering mechanism when compared to dry nonliving yeasts which did not usually accumulate more than 20 mg Cd/g. The uptake of cadmium was relatively fast, 75% of the sorption completed in less than 5 min. (c) 1993 Wiley & Sons, Inc.     

Real-time fuzzy-knowledge-based control of Baker's yeast production

A real-time fuzzy-knowledge-based system for fault diagnosis and control of bioprocesses was constructed using the object-oriented programming environment Small-talk/V Mac. The basic system was implemented in a Macintosh Quadra 900 computer and built to function connected on line to the process computer. Fuzzy logic was employed in handling uncertainties both in the knowledge and in measurements. The fuzzy sets defined for the process variables could be changed on-line according to process dynamics. Process knowledge was implemented in a graphical two-level hierachical knowledge base. In on-line process control the system first recognizes the current process phase on the basis of top-level rules in the knowledge-base. Then, according to the results of process diagnosis based on measurement data, the appropriate control strategy is subsequently inferred making use of the lower level rules describing the process during the phase in question. (c) 1995 John Wiley & Sons, Inc.     

Gas phase biotransformation reaction catalyzed by baker's yeast

The gas phase continuous production of acetaldehyde from ethanol and hexanol from hexanal using dried baker's yeast was studied as an alternative approach to conventional processes. The effects of water activity, activity of substrates, and amount of yeast on the performance of the continuous bioreactor were investigated. The extent of yeast hydration and ethanol activity are the most important factors affecting yeast activity and stability.     

Factors affecting the performance of crossflow filtration of yeast cell suspension

Factors affecting the performance of crossflow filtration were investigated with a thin-channel module and yeast cells. In crossflow filtration of Saccharomyces cerevisiae cells cultivated with YPD medium (Yeast extract, polypeptone, and dextrose) and suspended in saline, a steady state was attained within several minutes when the cell concentration was low and the circulation flow rate was high. The steady-state flux and the change in flux during the initial unsteady state were explained well by conventional filtration theory, with the amount of cake deposited and the mean specific resistance to the cake measured in a dead-end filtration apparatus used in calculation. When the circulation flow rate was lower than a critical value, a part of the channel of the crossflow filtration module was plugged with cell cake, and thus the steady-state flux was low. In crossflow filtration of suspensions of commercially available baker's yeast, the flux gradually decreased, and the flux after 8 h of filtration was lower than the value calculated by filtration theory. Fine particles contaminating the baker's yeast was responsible for the decrease. A similar phenomenon was responsible for the decrease. A similar phenomenon was observed in crossflow filtration of a broth of S. cerevisiae cells cultivated in molasses medium, which also contains such particles, had no effect of the permeation flux during crossflow filtration. (c) 1993 John Wiley & Sons, Inc.     

Reduction of α-Azidopropiophenone by Immobilized Baker's Yeast

Baker's yeast immobilized on montmorillonite K10 and chrysotile reduced α-azidopropiophenone to the corresponding azidoalcohols syn and anti with good chemical yield and enantiomeric excess.     

Sizing and counting of saccharomyces cerevisiae floc populations by image analysis, using an automatically calculated threshold

A standardized image analysis method has been developed permitting determination of the number of yeast flocs and their size distribution. The method includes image grabbing, image enhancement, automatic determination of the appropriate threshold, curve fitting of the areahistogram, determination of the mean single floc area and its standard deviation, and floc counting. The extension of the method to other applications is immediate and straightforward. Two Saccharomyces cerevisiae floc Populations (with ages of 48 and 72 h) were analyzed. The results showed a variation around the mean of 9%-12% for the single floc mean area, 6%-7% for the number of single flocs, and 5%-6% for the total number of flocs. Aggregates of two flocs (doublets) and three flocs (triplets) were enumerated. The correctness of the method was checked by analyzing the parameters of interest as a function of the threshold. The constant correlation between the parameters and the threshold showed the validity and consistency of the method. (c) 1996 John Wiley & Sons, Inc.     

In situ product removal using a crystallization loop in asymmetric reduction of 4-oxoisophorone by Saccharomyces cerevisiae

In situ product crystallization was investigated for solid product crystals that were obtained during fermentation. The model reaction was the asymmetric reduction of 4-oxoisophorone (OIP) using baker's yeast (S. cerevisiae) as a biocatalyst. The target product was 6R-dihydro-oxoisophorone (DOIP), also known as levodione, a key intermediate in carotenoid synthesis. DOIP was degraded by baker's yeast mainly to (4S,6R)-actinol, an unwanted byproduct in the process. Actinol formation reached up to 12.5% of the initial amount of OIP in the reactor during a batch process. However, better results were obtained when the dissolved DOIP concentration was controlled using an integrated fermentation-crystallization process because: (a) actinol formation was reduced to 4%; and (b) DOIP crystal formation in the reactor was avoided. DOIP productivity was improved by 50% and its selectivity was raised from 87% to 96% relative to the batch process. In the integrated process, most of the product was recovered as pure crystals; this may already minimize, if not eliminate, the need for organic solvents in the final purification steps. An almost sixfold reduction in biocatalyst consumption per kilogram product was achieved, which also can contribute to the minimization of waste streams.     

Improved production of ethyl-(R)-2-hydroxy-4-phenylbutyrate with pretreated Saccharomyces cerevisiae in water/organic solvent two-liquid phase systems

Baker's yeast pretreated with α-phenacyl chloride was employed to improve the enantioselectivity of the asymmetric reduction of ethyl-2-oxo-4-phenylbutyrate (EOPB) to ethyl-(R)-2-hydroxy-4-phenylbutyrate ((R)-EHPB) and maintain a high activity of the yeast. A water/organic solvent two-liquid phase system was also introduced to overcome the strong substrate and product inhibition of the enzyme; the highest catalytic activity and enantioselectivity were obtained in a water/benzene two-liquid phase system. When the reduction was catalyzed with pretreated yeast (300 mg mL^?1 buffer) in the water/benzene two-liquid phase system (V_aq/V_ben=20:40), 41.9% molar conversion of EOPB and 87.5% e.e. of (R)-EHPB were obtained in 48 h, using pH 8.0 phosphate buffer with 1.5% (v/v) of ethanol added as a co-substrate at 30°C, even with an initial EOPB concentration of 400 mM and a final EHPB concentration as high as 167.7 mM.     

Acquisition of thermotolerant yeast Saccharomyces cerevisiae by breeding via stepwise adaptation

A thermotolerant Saccharomyces cerevisiae yeast strain, YK60‐1, was bred from a parental strain, MT8‐1, via stepwise adaptation. YK60‐1 grew at 40°C, a temperature at which MT8‐1 could not grow at all. YK60‐1 exhibited faster growth than MT8‐1 at 30°C. To investigate the mechanisms how MT8‐1 acquired thermotolerance, DNA microarray analysis was performed. The analysis revealed the induction of stress‐responsive genes such as those encoding heat shock proteins and trehalose biosynthetic enzymes in YK60‐1. Furthermore, nontargeting metabolome analysis showed that YK60‐1 accumulated more trehalose, a metabolite that contributes to stress tolerance in yeast, than MT8‐1. In conclusion, S. cerevisiae MT8‐1 acquired thermotolerance by induction of specific stress‐responsive genes and enhanced intracellular trehalose levels. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1116–1123, 2013     

Fluxes of carbon, phosphorylation, and redox intermediates during growth of saccharomyces cerevisiae on different carbon sources

In the present work we develop a method for estimating anabolic fluxes when yeast are growing on various carbon substrates (glucose, glycerol, lactate, pyruvate, acetate, or ethanol) in minimal medium. Fluxes through the central amphibolic pathways were calculated from the product of the total required amount of a specified carbon intermediate times the growth rate. The required amount of each carbon intermediate was estimated from the experimentally determined macromolecular composition of cells grown in each carbon source and the monomer composition of macromolecules.Substrates sharing most metabolic pathways such as ethanol and acetate, despite changes in the macromolecular composition, namely carbohydrate content (34% +/- 1 and 21% +/- 3, respectively), did not show large variations in the overall fluxes through the main amphibolic pathways. For instance, in order to supply anabolic precursors to sustain growth rates in the range of 0.16/h to 0.205/h, similar large fluxes through Acetyl CoA synthase were required by acetate (4.2 mmol/hr g dw) or ethanol (5.2 mmol/h g dw).The V(max) activities of key enzymes of the main amphibolic pathways measured in permeabilized yeast cells allowed to confirm, qualitatively, the operation of those pathways for all substrates and were consistent on most substrates with the estimated fluxes required to sustain growth.When ATP produced from oxidation of the NADH synthesized along with the key intermediary metabolites was taken into account, higher Y(ATP) (max) values (36 with respect to 24 g dw/mol ATP) were obtained for glucose. The same result was obtained for glycerol, ethanol, and acetate. A yield index (YI) was defined as the ratio of the theoretically estimated substrate flux required to sustain a given growth rate over the experimentally measured flux of substrate consumption. Comparison of Yl between growth on various carbon sources led us to conclude that ethanol (Yl = 0.84), acetate (Yl = 0.77), and lactate (Yl = 0.77) displayed the most efficient use of substrate for biomass production. For the other substrates, the Yl decayed in the following order: pyruvate > glycerol > glucose.An improvement of the quantitative understanding of yeast metabolism, energetics, and physiology is provided by the present analysis. The methodology proposed can be applied to other eukaryotic organisms of known chemical composition. (c) 1995 John Wiley & Sons, Inc.     

Removal of heavy metals using a brewer's yeast strain of Saccharomyces cerevisiae: advantages of using dead biomass

Aim:  The capacities of live and heat-killed cells of Saccharomyces cerevisiae at 45°C for the removal of copper, nickel and zinc from the solution were compared.
Methods and Results:  Kinetic studies have shown a maximum accumulation of Ni²⁺ and Zn²⁺ after 10 min for both types of cells, while for Cu²⁺ this was attained after 30 and 60 min for dead and live cells, respectively. Equilibrium studies have shown that inactivated biomass displayed a greater Zn²⁺ and Ni²⁺ accumulation than live yeasts. For Cu²⁺, live and dead cells showed similar accumulation. Fluorescence, scanning electron microscopy and infrared spectroscopy studies have shown that no appreciable structural or molecular changes occurred in the cells during the killing process. The increased metal uptake observed in dead cells can be most likely explained by the loss of membrane integrity, which allows the exposition of further metal-binding sites present inside the cells.
Conclusions:  Heat-killed cells showed a higher degree of heavy metal removal than live cells, being more suitable for further bioremediation works.
Significance and Impact of the Study:  Dead flocculent cells can be used in a low cost technology for detoxifying metal-bearing effluents as this approach combines an efficient metal removal with the ease of cell separation.     

Differences between pectic enzymes produced by laboratory and wild-type strains of Saccharomyces cerevisiae

The laboratory strain of S. cerevisiae, IM1-8b, showed pectolytic activity in the presence of either glucose, fructose, or sucrose as the carbon source, but not with galactose. The enzyme activity was rapidly lost with shaking. The optimum pH and temperature for activity were 4.5 and 45°C, respectively. The enzyme was an endopolygalacturonase, since it preferentially hydrolysed pectate over pectin and decreased the viscosity of a 5% polygalacturonic solution by about 30% in 30min producing oligogalacturonic acid and digalacturonic acid as end-products.     

De novo synthesis of monoterpenes by Saccharomyces cerevisiae wine yeasts

This paper reports the production of monoterpenes, which elicit a floral aroma in wine, by strains of the yeast Saccharomyces cerevisiae. Terpenes, which are typical components of the essential oils of flowers and fruits, are also present as free and glycosylated conjugates amongst the secondary metabolites of certain wine grape varieties of Vitis vinifera. Hence, when these compounds are present in wine they are considered to originate from grape and not fermentation. However, the biosynthesis of monoterpenes by S. cerevisiae in the absence of grape derived precursors is shown here to be of de novo origin in wine yeast strains. Higher concentration of assimilable nitrogen increased accumulation of linalool and citronellol. Microaerobic compared with anaerobic conditions favored terpene accumulation in the ferment. The amount of linalool produced by some strains of S. cerevisiae could be of sensory importance in wine production. These unexpected results are discussed in relation to the known sterol biosynthetic pathway and to an alternative pathway for terpene biosynthesis not previously described in yeast.     

A Multivariate Re-Examination of Experimental Condition Effects on Acyloin-Type Condensation Mediated by Saccharomyces Cerevisiae

Statistical methods of optimization were applied to the stereoselective synthesis of (2S,3R)-5-phenylpent-4-en-2,3-diol mediated by baker's yeast. The quantitative effects of seven variables, i.e. pH, temperature, concentration of cinnamaldehyde, yeast and glucose, addition of pyruvate and acetaldehyde were investigated using a fractional factorial design. This approach gave informations about the chemical behaviour of the yeast. Response surface methodology was employed to describe the variability of the yield in the experimental domain.     

Reductive biotransformation by wild type and mutant strains of Saccharomyces cerevisiae in aqueous-organic solvent biphasic systems

Whole cells of Saccharomyces cerevisiae analyzed the conversion of benzaldehyde to benzyl alcohol in aqueous-organic biphasic media. Reaction rate increased dramatically as moisture content of the solvent was increased in the range 0% to 2%. The highest biotransformation rates were observed when hexane was used as organic solvent. Benzaldehyde was also converted to benzyl alcohol by a cell-free crude extract in biphasic systems containing hexane, although the rate of product formation was much lower. Mutant strains of S. cerevisiae lacking some or all of the ADH isoenzymes, ADH I, II, and III, manifested similar rates for bioconversion of benzaldehyde to benzyl alcohol in both aqueous and two-phase systems. In general, conversion rates observed in aqueous media were 2 to 3 times higher than those observed in hexane containing 2% moisture.     

Studies of the reductive biotransformation of selected carbonyl compounds by whole cells and extracts of baker's yeast, Saccharomyces carevisiae

The progress of reductive biotransformations of a variety of earbonyl compounds by whole cells of baker's yeast was monitored with time. Biotransformations rates ranged from 0.11 to 112.12 mg product formed per g dry yeast per h. While rapid biotransformations of citronellal and ethyl benzoylformate were observed, complete conversion of substrate to product did not occur. Reductive conversions of ethyl- and methyl-acetoacetate went to completion in 6 and 12 h respectively. Ethyl mandelate was produced stereoselectively, favoring the (R)- stereoisomer and ethyl and methyl-3-hydroxybutyrate were produced with (S)-enantiospecificity. Yeast crude extract and resuspended presence of NAD(P)H. Ethyl benzoylformate and methyl-and ethyl-acetoacetate were preferentially reduced by yeast crude extract as compared to resuspended pellet and, in the case of the former two substrates, the reaction manifested a preference for NADPH over NADH.     

Saccharomyces cerevisiae: the effect of different forms and concentrations of iodine on uptake and yeast growth

The essentiality of iodine for humans, especially in the early stages of life, is well recognized. The chemical forms of iodine in food supplements, infant formulae and iodated salt are either iodide (KI) or iodate (KIO₃). Because there are no or rare data about iodine uptake by yeasts, we investigated the influence of different sources of iodine, as KI, KIO₃ and periodate (KIO₄), on its uptake in and growth of the model yeast Saccharomyces cerevisiae . KIO₃ inhibited the growth of the yeast the most and already at a 400 μM initial concentration in the growth medium; the OD was reduced by 23% in comparison with the control, where no KIO₃ was added. The uptake of different iodine sources by the yeast S. cerevisiae was minimal, in total <1%. Tracer experiments with radioactive ¹³¹I added as KI showed that the yeast S. cerevisiae does not have the ability to transform KI into volatile species. We investigated the specificity of iodine uptake added as KIO₃ in the presence of Na₂SeO₄ or ZnCl₂ or K₂CrO₄ in the growth medium, and it was found that chromate had the most influence on reduction of KIO₃ uptake.     

Enhancement of maltose utilisation by Saccharomyces cerevisiae in medium containing fermentable hexoses

Saccharomyces cerevisiae are unable to maintain high rates of fermentation during transition from catabolism of hexoses to maltose. This phenomenon, termed ‘maltose lag’, presents problems for the baking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and α-glucosidase (maltase), encoded by MAL genes. Synthesis of these is induced by maltose and repressed by glucose. One strain of baker’s yeast used in this work exhibited a marked maltose lag, whereas a second strain exhibited a shorter lag during conversion from hexose to maltose metabolism. The extent of the lag was linked to the levels of maltose permease and maltase in cells at the time of inoculation into mixed sugar medium. This view is supported by results showing that pulsing yeast with maltose to induce expression of MAL genes prior to inoculation into mixed sugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could therefore be useful for enhancing some fermentations relevant to baking and other yeast industries. Received 24 December 1988/ Accepted in revised form 18 March 1999     

Ultrastructural effects of pressure stress to the nucleus in Saccharomyces cerevisiae: a study by immunoelectron microscopy using frozen thin sections

Abstract The effects of hydrostatic pressure on subcellular structures, particularly the nucleus, of Saccharomyces cerevisiae were investigated by immunoelectron microscopy. Cells were treated with hydrostatic pressure from 0.1 to 400 MPa for 10 min at room temperature. Frozen thin sections of the cells revealed that spindle pole bodies disappeared at 100 MPa. At 150 MPa, the deposition of gold panicles for anti α-tubulin was noticed in the nucleus, although the filamentous structure of microtubules was lost. At 200 MPa, fewer gold particles were scattered in the nucleus and the nuclear membrane in several portions was also observed to be open at 300 MPa. These results show that elements of the nuclear division apparatus were susceptible to pressure stress, particularly spindle pole bodies and microtubules. The damage to spindle pole bodies, microtubules, and nuclear membrane caused by pressure stress was followed by the inhibition of nuclear division. After the release of pressure, the spindle pole bodies and microtubules of pressurized cells at below 200 MPa regained their normal appearance at 24 h.