Alexander Rapoport

Interrelations of the yeast Candida utilis and Cr(VI): metal reduction and its distribution in the cell and medium

Abstract An effect of chromium(VI) ions on the growth and bioaccumulation properties of growing cells of Candida Utilis was studied. Molasses media for yeast growth containing 20 g glucose l −1 and 50+500 mg Cr(VI) l −1 were used in batch cultivation. Addition of 100 mg Cr(VI) l −1 resulted in a threefold decrease in the cell concentration, as compared with the culture grown without metal. Cr(VI) inhibited culture growth in a concentration-dependent manner, this dependence was not linear. Glucose consumption by growing cells depended on the initial Cr(VI) concentration in the medium and correlated with growth activity. No inhibitory effect of high Cr(VI) concentrations on the activity of some exo-enzymes of C. utilis cells was observed. During C. utilis cultivation, Cr(VI) was partially reduced to an ultimate Cr(III) in all tested ranges of the Cr(VI) concentrations. The specific chromium uptake by cells was detected in biomass that grew in the presence of 100+300 mg Cr(VI) l −1 in a period of 48–96 h. The highest values were achieved after 96 h growth in the presence of 200 and 300 mg Cr(VI) l −1 , and were 7.3 and 7.2 mg Cr g dw l −1 , respectively. Electron microscopic observations showed morphological changes in yeast cells to be more pronounced upon culture growth with 100–300 mg Cr(VI) l −1 than in the cells subjected to higher metal concentrations. The conclusion has been made that the mechanism of the Cr(VI) toxic effect on the growing yeast cells can vary in dependence of the metal concentration.

Biosorption of hexavalent chromium by yeasts

Abstract Different species of yeast exhibit noticeable differences in their ability to sorb Cr(VI). The sorption ability of dehydrated cells is considerably higher than that of intact cells and optimal sorption of chromium takes place at physiological (30°C) or elevated (45°C) temperatures.

Characteristics of cellular membranes at rehydration of dehydrated yeast Saccharomyces cerevisiae

SummaryThis paper describes the characteristics of the structural and functional organization of cellular membranes rehydrated after dehydration of the yeast Saccharomyces cerevisiae. It was noted that dehydration and subsequent rehydration of yeast cells causes a considerable increase of cytoplasmic membrane permeability. Addition of CaCl2, glucose and polyethyleneglycol to the rehydration medium caused a decrease in cell permeability, assessed as the losses of potassium ions, nucleotides, as well as the total losses of intracellular compounds. KCl had a positive effect only at concentrations above 10%. Yeast cells, dried to residual moisture lower than 20%, showed a decrease in membrane permeability as temperatures of the rehydration medium increased up to 38°–43°C. Upon reactivation of viable dehydrated cells in a nutrient medium, a reparation of the structural damages of various intracellular membranes takes place. It was established that at cell dehydration to residual moistures of 8%–12% all the free and a part of bound water is evaporated from cells.

Effect of xylitol and trehalose on dry resistance of yeasts

Abstract The effects of dehydration/rehydration on two strains of Saccharomyces cerevisiae: S600, a metabolically engineered xylose-utilising strain, and H158, the non-xylose-utilising host strain; and on the naturally xylose-utilising yeast Pachysolen tannophilus CBS 4044, were compared after glucose and xylose utilisation respectively. The yeast strains differed in their ability to excrete and accumulate intracellular xylitol. A high intracellular xylitol content before and after dehydration coincided with a higher viability after a dehydration/rehydration cycle. The intracellular trehalose content increased during dehydration in all three yeast strains, but this did not correspond to enhanced cell viability after dehydration/rehydration. The results are discussed in relation to the ability of xylitol and trehalose to structure water.

Survival kit of Saccharomyces cerevisiae for anhydrobiosis

Yeast cells are well adapted to interfacial habitats, such as the surfaces of soil or plants, where they can resist frequent fluctuations between wet and dry conditions. Saccharomyces cerevisiae is recognized as an anhydrobiotic organism, and it has been the subject of numerous studies that aimed to elucidate this ability. Extensive data have been obtained from these studies based on a wide range of experimental approaches, which have added significantly to our understanding of the cellular bases and mechanisms of resistance to desiccation. The aim of this review is to provide an integrated view of these mechanisms in yeast and to describe the survival kit of S. cerevisiae for anhydrobiosis. This kit comprises constitutive and inducible mechanisms that prevent cell damage during dehydration and rehydration. This review also aims to characterize clearly the phenomenon of anhydrobiosis itself based on detailed descriptions of the causes and effects of the constraints imposed on cells by desiccation. These constraints mainly lead to mechanical, structural, and oxidative damage to cell components. Considerations of these constraints and the possible utilization of components of the survival kit could help to improve the survival of sensitive cells of interest during desiccation.

Cr(VI) sorption by intact and dehydrated Candida utilis cells in the presence of other metals

This study examined the Cr(VI), Cu(II), Zn(II), Cd(II), Pb(II) sorption by intact and dehydrated Candida utilis cells. The anion [Cr2O7]2− and cation Me2+ sorption kinetics was investigated in both single- and dual-metal situations. Uptake of chromate anions occurred much more slowly singularly than with metal cations. A combination of Pb or Cu and chromate anions gave a synergistic effect for Cr(VI) sorption, but not Cd and Zn, which inhibited Cr(VI) sorption by dehydrated cells. The use of alcian blue to occupy maximum vacant adsorption sites on the cell surface unexpectedly did not influence further adsorption of Me2+. Metal uptake by C. utilis was 7 mg (135 μM) Cr, 23 mg (362 μM) Cu, 39 mg (188 μM) Pb, 19 mg (170 μM) Cd, 28 mg (428 μM) Zn gdw−1. Estimations of the number and area of metal ions occupying the cell surface was made and data obtained indicated that area of sorbed Cr(VI), Cd(II), Cu(II), Pb(II) occupied the single cell did not cover all the surface, whereas Zn(II) covered up to 168%.

The role of glycerol transporters in yeast cells in various physiological and stress conditions

Small and uncharged glycerol is an important molecule for yeast metabolism and osmoadaptation. Using a series of S. cerevisiae BY4741-derived mutants lacking genes encoding a glycerol exporter (Fps1p) and/or importer (Stl1p) and/or the last kinase of the HOG pathway (Hog1p), we studied their phenotypes and various physiological characteristics with the aim of finding new roles for glycerol transporters. Though the triple mutant hog1Δ stl1Δ fps1Δ was viable, it was highly sensitive to various stresses. Our results showed that the function of both Stl1p and Fps1p transporters contributes to the cell ability to survive during the transfer into the state of anhydrobiosis, and that the deletion of FPS1 decreases the cells tolerance of hyperosmotic stress. The deletion of STL1 results in a slight increase in cell size and in a substantial increase in intracellular pH. Taken together, our results suggest that the fluxes of glycerol in both directions across the plasma membrane exist in yeast cells simultaneously, and the export or import predominates according to the actual specific conditions.

Anhydrobiosis in yeast: Stabilization by exogenous lactose

We have found that incubation in lactose solutions (0.75 M) of yeast culture Saccharomyces cerevisiae sensitive to dehydration damage increased the stability of the cells during dehydration. Simultaneously with this increase in viability, a decrease in plasma membrane permeability during rehydration was seen. Using Fourier transform infrared spectroscopy to measure lipid phase transitions, we observed that the lactose treatment depressed the membrane phospholipid phase transition temperature in a sensitive culture of dry yeast. As a result, it leads to the decrease in the damages of molecular organization of membranes during rehydration of dry yeast cells, thus reducing leakage from the cells.

Attachment of yeast to modified stainless steel wire spheres, growth of cells and ethanol production

Abstract The immobilization of yeast Saccharomyces cerevisiae, their growth and ethanol production were investigated using untreated and modified stainless steel wire spheres (WS) as carriers. The carrier surface was modified by oxidation, by treatment with titanium (IV) chloride (TiCl4) or by γ-aminopropyltrietoxysilane (AS) in an attempt to raise the efficiency of the immobilization of the yeast cells. The influence of the cell fixation method on culture growth and ethanol synthesis was investigated. The immobilization of cells to carrier surface was checked by scanning electron microscopy (SEM). More closely attachment of yeast cells was seen on the aminated wire surface. It was established that during fermentation ethanol production by yeast was stimulated using immobilized cells in oxidized WS or treated with TiCl4. Aminated WS surface stimulated the culture growth but decreased ethanol synthesis. Free yeast cells located in the pores of WS increased the biomass concentration and ethanol production only during the first cycle of batch fermentation. Stable cell growth and ethanol production was observed during subsequent 4–5 repeated fermentation cycles using washing out of free cells from WS before fermentation. The system productivity Qeth for ethanol synthesis was 0.92–1.25 g/l per h. Cell fixation in WS by lyophilization or convective dehydration improved cell attachment to wire surface but did not influence positively culture growth and ethanol synthesis. The conclusion was made that stainless steel WS filled with paste-like yeast biomass can be used as inoculum for repeated batch ethanol production. The modification method of the stainless steel wire surface significantly influences the immobilization efficiency of yeasts. Oxidized or modified by TiCl4 wire surface and washing out free cells from WS can be recommended for ethanol production by immobilized yeasts.

Effects of yeast immobilization on bioethanol production

The current study evaluated a newer method, which includes a dehydration step, of immobilizing Saccharomyces cerevisiae L‐77 and S. cerevisiae L‐73 onto hydroxylapatite and chamotte ceramic supports. The efficiency of cell immobilization on chamotte was significantly higher than hydroxylapatite. Immobilized yeast preparations were investigated for their ethanol‐producing capabilities. The glucose concentration in a fermentation medium was 100 mg/mL. Immobilized preparations produced the same amount of ethanol (48 ± 0.5 mg/mL) as free cells after 36 H of fermentation. During the early stages of fermentation, immobilized yeast cells produced ethanol at a higher rate than free cells. Yeast preparations immobilized on both supports (hydroxylapatite and chamotte) were successfully used in six sequential batch fermentations without any loss of activity. The chamotte support was more stable in the fermentation medium during these six cycles of ethanol production. In addition to the high level of ethanol produced by cells immobilized on chamotte, the stability of this support and its low cost make it a promising material for biotechnologies associated with ethanol production.