The removal and recovery of toxic and valuable metals from aqueous solutions by the yeast Saccharomyces cerevisiae
- Authors: Wilhelmi, Brendan Shane
- Date: 1998
- Subjects: Saccharomyces cerevisiae , Yeast fungi -- Biotechnology , Sewage -- Purification -- Heavy metals removal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4002 , http://hdl.handle.net/10962/d1004062 , Saccharomyces cerevisiae , Yeast fungi -- Biotechnology , Sewage -- Purification -- Heavy metals removal
- Description: This project considered the use of the yeast Saccharomyces cerevisiae as a biosorbent for the removal and recovery of a range of metals from contaminated waters. S. cerevisiae, as a biosorbent, has the potential to provide a cost effective, selective and highly efficient purification system. Initial studies focused on metal accumulation by an immobilized baker's S. cerevisiae biosorbent. The parameters affecting metal uptake were investigated, these included metal concentration, time and solution pH. Metal uptake was rapid. Gold and cobalt reached saturation within 5 min of contact with the biosorbent in batch reactors. Copper, zinc, nickel, cadmium and chromium reached saturation within 30 min of contact. Metal accumulation was pH dependent and was generally unaffected at a solution pH ≥ 4, and was substantially decreased at pH ≤ 2. The exception was gold which was preferentially accumulated at a solution pH of 2. The immobilized baker's yeast accumulated metals with maximum binding capacities in the order of gold > cadmium > cobalt > zinc > copper > chromium > nickel. A rapid method to assess metal recovery was developed. Bioaccumulated metal was efficiently recovered using dilute mineral acids. Copper recovery of ≥ 80 % was achieved by decreasing the solution pH of the reaction mixture to 2 with the addition of nominal quantities of HCl, H₂SO₄ or RNO₃. Adsorption-desorption over 8 cycles had no apparent adverse effect on metal uptake or recovery in batch reactors. Transmission electron microscopy showed no evidence of damage to cells used in copper adsorption-desorption investigations. Biosorption columns were investigated as bioreactors due to their application potential. The metals investigated were effectively removed from solution. At a saturation threshold, metal uptake declined rapidly. Most metals investigated were desorbed from the columns by eluting with 0.1 M HCl. Initially recoveries of copper, cobalt and cadmium were as high as 100%. Desorbed copper, zinc, cadmium, nickel and cobalt were concentrated in 10 to 15 ml of eluent, representing up to a 40 fold decrease in solution volume. Cadmium, nickel and zinc uptake increased with the second application to the columns. Initial accumulation of gold and chromium was 42.2 μmol/g and 28.6 μmol/g, however, due to the low recoveries of these two metals, a second application was not investigated. Copper was applied to a single column for 8 consecutive adsorption-desorption cycles. Uptake increased from an initial 31.3 μmol/g to 47.8 μmol/g at cycle 7. The potential for selective metal recovery was demonstrated using two biosorption columns in series. Copper was accumulated and recovered most efficiently. Zinc, cobalt and cadmium were displaced to the second column. Copper bound preferentially to zinc at a ratio of 6:1. Copper bound preferentially to cobalt at a ratio of 4:1. Cadmium was only displaced at a ratio of 2:1. The successful transfer of the bioremediation technology from the laboratory to an industrial application has yet to be realized. Bioremediation of a Plaatjiesvlei Black Mountain mine effluent, which contained copper, zinc, lead and iron, was investigated in this project. The removal of the metals was most effective at pH 4. A combined strategy of pH adjustment and bioremediation using immobilized S. cerevisiae decreased the copper concentration by 92.5%, lead was decreased by 90% and zinc was decreased by 60%. Iron was mostly precipitated from solution at pH ≥ 4. An ageing pond at the mine with conditions such as; pH, water volume and metal concentration, which were more conducive to biological treatment was subsequently identified. The investigation indicated a possible application of the biomass as a supplement to chemical remediation. The metal removal capability of a waste brewer's yeast was subsequently investigated. A yeast conditioning step increased metal uptake up to 100% and enhanced reproducibility. Metal removal from solution was rapid and pH dependent. The metals were efficiently removed from solution at pH ≥ 4. Uptake was substantially inhibited at pH ≤ 3. The waste brewer's yeast accumulated metals with maximum binding capacities in the order of copper (25.4 μmol/g) > lead (19.4 μmol/g) > iron (15.6 μmol/g) > zinc (12.5 μmol/g). No correlation between cell physiology and metal uptake was observed. Uptake of the four metals was confirmed by energy dispersive X-ray microanalysis. The interference of lead, zinc and iron on copper uptake by the waste brewer's yeast, and the interference of copper on the uptake of lead, zinc and iron was investigated. Maximum copper uptake was not decreased in the presence of lead. The Bmax remained constant at approximately 25 μmol/g. The dissociation constants increased with increasing lead concentrations. Lead bioaccumulation was significantly decreased in the presence of copper. The type of inhibition was dependent on the initial copper concentrations. Zinc had a slight synergistic effect on copper uptake. The copper Bmax increased from 30.8 μmol/g in a single-ion system to 34.5 μmol/g in the presence of 200 μmol/l of zinc. Zinc uptake was severely inhibited in the presence of copper. The maximum uptake and dissociation constant values were decreased in the presence of copper, which suggested an uncompetitive inhibition. The affinity of copper was substantially higher than zinc. The presence of higher levels of copper than zinc in the yeast cells was confirmed by energy dispersive microanalysis. Copper uptake was decreased in the presence of iron, with the copper Bmax being decreased from 25.4 μmol/g in a single-ion system to 20.1 μmol/g in the presence of 200 μmol/l iron. Iron Bmax values remained constant at 16.0 μmol/g. Combined biosorption and EDXA results suggested the iron bound at a higher affinity than copper to the cell wall. Total copper removal was higher as larger quantities of copper were deposited in the cell cytoplasm. Metal removal from the Plaatjiesvlei effluent by free cell suspensions of the waste brewer's yeast was satisfactory. Copper levels were decreased by 96%, iron by 42%, lead 25% and zinc 2%. Waste brewer's yeast is a cheap source of biomass in South Africa, and could potentially provide the basis for the development of an innovative purification system for metal-contaminated waters.
- Full Text:
- Date Issued: 1998
Bioaccumulation of metal cations by yeast and yeast cell components
- Authors: Brady, Dean
- Date: 1993
- Subjects: Yeast , Yeast fungi -- Biotechnology , Cations , Metal ions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4046 , http://hdl.handle.net/10962/d1004107 , Yeast , Yeast fungi -- Biotechnology , Cations , Metal ions
- Description: The aim of the project was to determine whether a by-product of industrial fermentations, Saccharomyces cerevisiae, could be utilized to bioaccumulate heavy metal cations and to partially define the mechanism of accumulation. S. cerevisiae cells were found to be capable of accumulating Cu²⁺in a manner that was proportional to the external Cu²⁺ concentration and inversely proportional to the concentration of biomass. The accumulation process was only minimally affected by temperature variations between 5 and 40°C or high ambient concentrations of sodium chloride. The accumulation process was however considerably affected by variations in pH, bioaccumulation being most efficient at pH 5 - 9 but becoming rapidly less so at either extreme of pH. Selection for copper resistant or tolerant yeast diminished the yeast's capacity for Cu²⁺ accumulation. For this and other reasons the development of heavy metal tolerance in yeasts was deemed to be generally counterproductive to heavy metal bioaccumulation. The yeast biomass was also capable of accumulating other heavy metal cations such as c0²⁺ or Cd²⁺. The yeast biomass could be harvested after bioaccumulation by tangential filtration methods, or alternatively could be packed into hollow fibre microfilter membrane cartridges and used as a fixed-bed bioaccumulator. By immobilizing the yeast in polyacrylamide gel and packing this material into columns, cu²⁺, C0²⁺ or Cd²⁺ could be removed from influent aqueous solutions yielding effluents with no detectable heavy metal, until breakthrough point was reached. This capacity was hypothesized to be a function of numerous "theoretical plates of equilibrium" within the column. The immobilized biomass could be eluted with EDTA and recycled for further bioaccumulation processes with minor loss of bioaccumulation capacity. Yeast cells were fractionated to permit identification of the major cell fractions and molecular components responsible for metal binding. Isolation of the yeast cell walls permitted investigation of their role in heavy metal accumulation. Although the amino groups of chitosan and proteins, the carboxyl groups of proteins, and the phosphate groups of phosphomannans were found to be efficient groups for the accumulation of copper, the less effective hydroxyl groups of the carbohydrate polymers (glucans and mannans) had a similar overall capacity for copper accumulation owing to their predominance in the yeast cell wall. The outer (protein-mannan) layer of the yeast cell wall was found to be a better Cu²⁺ chelator than the inner (chitinglucan) layer. It appeared that the physical condition of the cell wall may be more important than the individual macromolecular components of the cell wall in metal accumulation. It was apparent that the cell wall was the major, if not the sole contributor to heavy metal accumulation at low ambient heavy metal concentrations. At higher ambient metal concentrations the cytosol and vacuole become involved in bioaccumulation. Copper and other metals caused rapid loss of 70% of the intracellular potassium, implying permeation of the plasma membrane. This was followed by a slower "leakage" of magnesium from the vacuole which paralleled Cu²⁺ accumulation, suggesting that it may represent some form of ion-exchange. An intracellular copper chelating agent of approximately 2 kDalton molecular mass was isolated from copper tolerant yeast. This chelator was not a metallothionein and bound relatively low molar equivalents of copper compared to those reported for metallothionein. Treatment of the biomass with hot alkali yielded two biosorbents, one soluble (which could be used as a heavy metal flocculent), and an insoluble biosorbent which could be formed into a granular product to be used in fixed-bed biosorption columns. The granular biosorbent could accumulate a wide range of heavy metal cations in a semispecific manner and could be stored in a dehydrated form indefinitely, and rehydrated when required. Bioaccumulation by live algae was investigated as an alternative to yeast based processes. Various strains of algae, of which Scenedesmus and Selenastrum were the most effective, were found to be capable of accumulating heavy metals such as Cu²⁺, Pb²⁺ and Cr³⁺.
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- Date Issued: 1993
Hybridization studies within the genus Kluyveromyces van der Walt emend. van der Walt
- Authors: Johannsen, Elz̀bieta
- Date: 1979
- Subjects: Yeast fungi -- Biotechnology , Yeast fungi -- Genetics , Yeast fungi -- Hybridization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4123 , http://hdl.handle.net/10962/d1013400
- Description: Hybridization studies based on the prototrophic selection technique, involving the use of auxotrophic mutants of strains of all accepted species of the genus Kluyveromyces, are reported. Two main groups of mutually interfertile taxa were established within the genus. The first group comprises Kluyveromyces bulgaricus, Kluyveromyces cicerisporus, Kluyveromyces dobzhanskii, Kluyveromyces drosophilarum, Kluyveromyces fragilis, Kluyveromyces lactis, Kluyveromyces marxianus, Kluyveromyces phaseolosporus, Kluyveromyces vanudenii and Kluyveromyces wikenii. The second group consists of Kluyveromyces dabzhanskii, Kluyveromyces drosophilarum, Kluyveromyces laotis, Kluyveromyces vanudenii and Kluyveromyces wiokerhamii. Hybrids were also detected in crosses involving Kluyveromyces drosophilarum and Kluyveromyces waltii as well as Kluyveromyces marxianus and Kluyveromyces thermotolerans. In terms of the concept of the biological species and in compliance with the requirements of the International Code of Botanical Nomenclature, taxa which hybridize with Kluyveromyces marxianus and form fertile recombinants at frequencies observed in intraspecific crosses, are accepted as varieties of Kluyveromyces marxianus. Hybridization was observed between Kluyveromyces marxianus var. lactis and the presumed imperfect forms of some Kluyveromyces species, namely Candida kefyr, Candida macedoniensis and Torulopsis sphaerica. Recombination was not detected in crosses involving Kluyveromyces marxianus var. marxianus and representatives of other yeast genera, i.e. Pichia, Saccharomyces, Torulaspora and Zygosaccharomyces. Conclusions regarding the relationship between members of the genus Kluyveromyces, reached on the basis of this investigation are compared with those reported by other workers, who based their investigations on phenotypic characteristics as well as on the determinations of mol % G+C and DNA-DNA homology studies.
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- Date Issued: 1979