An investigation into the synergistic action of cellulose-degrading enzymes on complex substrates
- Authors: Thoresen, Mariska
- Date: 2015
- Subjects: Lignocellulose , Biomass energy , Cellulosic ethanol , Saccharomyces cerevisiae , Cellulase , Enzymes -- Biotechnology , Hydrolases
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4154 , http://hdl.handle.net/10962/d1017915
- Full Text:
- Date Issued: 2015
- Authors: Thoresen, Mariska
- Date: 2015
- Subjects: Lignocellulose , Biomass energy , Cellulosic ethanol , Saccharomyces cerevisiae , Cellulase , Enzymes -- Biotechnology , Hydrolases
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4154 , http://hdl.handle.net/10962/d1017915
- Full Text:
- Date Issued: 2015
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
- 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
The effect of hydrostatic carbon dioxide pressure and extracellular ethanol on the performance of the yeast strain Saccharomyces cerevisiae during fermentation
- Authors: Longden, Nicholas Guy
- Date: 1993
- Subjects: Brewing -- Microbiology , Yeast , Fermentation , Saccharomyces cerevisiae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4044 , http://hdl.handle.net/10962/d1004105 , Brewing -- Microbiology , Yeast , Fermentation , Saccharomyces cerevisiae
- Description: The brewing industry constantly experiences problems in trying to maintain the quality of beer produced. Unfavourable conditions during fermentation may alter the performance of the yeast strain Saccharomyces cerevisiae, resulting in a "poor" end-product. It has been established that high concentrations of extracellular ethanol, when added to the fermentation medium inhibit yeast activity. It has been recently suggested that increased carbon dioxide pressure could inactivate the yeast activity adding to further brewing problems. The aim of this study was to investigate the effect of extracellular carbon dioxide pressure and ethanol addition, on yeast performance when added to a fermentation medium, and to establish whether an inhibitory relationship existed between ethanol and carbon dioxide pressure, when combined and added to the fermentation medium. Dissolved C0₂ in the medium, medium pH and substrate utilisation were analysed daily during a fermentation, as were membrane fatty acid composition. These parameters were used to assess the effect of ethanol and carbon dioxide on the yeast performance and consequently the final end-product. Supplementing the medium with extracellular ethanol, even as low as 5%, was shown to inhibit yeast performance during fermentation. This effect was even more marked as the ethanol concentration was increased, with almost total inhibition of yeast activity occuring after the addition of 15% ethanol (v/v). A similar effect was observed when elevated C0₂ pressures were applied to the medium, and although low C0₂ pressures initially induced the synthesis of saturated yeast membrane fatty acids, elevated C0₂ pressures (greater than 1,0 atm.) was shown to follow a similar inhibitory trend, if not as dramatic, as ethanol. A combination of both ethanol and C0₂ pressure showed a further increase in the level of yeast inhibition, although the low C0₂ pressure appeared to initially inhibit the toxicity of ethanol on the yeast. Increasing the levels of the C0₂/ethanol treatment (1,0 atm.), showed a synergistic effect on yeast performance. The results of this study indicate that both extracellular ethanol and carbon dioxide do appear to inhibit yeast performance and affect membrane fatty acid composition of the cells by inhibiting the synthesis of the respective fatty acid. This affect has a significant bearing on the general metabolism of the yeast cell.
- Full Text:
- Date Issued: 1993
- Authors: Longden, Nicholas Guy
- Date: 1993
- Subjects: Brewing -- Microbiology , Yeast , Fermentation , Saccharomyces cerevisiae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4044 , http://hdl.handle.net/10962/d1004105 , Brewing -- Microbiology , Yeast , Fermentation , Saccharomyces cerevisiae
- Description: The brewing industry constantly experiences problems in trying to maintain the quality of beer produced. Unfavourable conditions during fermentation may alter the performance of the yeast strain Saccharomyces cerevisiae, resulting in a "poor" end-product. It has been established that high concentrations of extracellular ethanol, when added to the fermentation medium inhibit yeast activity. It has been recently suggested that increased carbon dioxide pressure could inactivate the yeast activity adding to further brewing problems. The aim of this study was to investigate the effect of extracellular carbon dioxide pressure and ethanol addition, on yeast performance when added to a fermentation medium, and to establish whether an inhibitory relationship existed between ethanol and carbon dioxide pressure, when combined and added to the fermentation medium. Dissolved C0₂ in the medium, medium pH and substrate utilisation were analysed daily during a fermentation, as were membrane fatty acid composition. These parameters were used to assess the effect of ethanol and carbon dioxide on the yeast performance and consequently the final end-product. Supplementing the medium with extracellular ethanol, even as low as 5%, was shown to inhibit yeast performance during fermentation. This effect was even more marked as the ethanol concentration was increased, with almost total inhibition of yeast activity occuring after the addition of 15% ethanol (v/v). A similar effect was observed when elevated C0₂ pressures were applied to the medium, and although low C0₂ pressures initially induced the synthesis of saturated yeast membrane fatty acids, elevated C0₂ pressures (greater than 1,0 atm.) was shown to follow a similar inhibitory trend, if not as dramatic, as ethanol. A combination of both ethanol and C0₂ pressure showed a further increase in the level of yeast inhibition, although the low C0₂ pressure appeared to initially inhibit the toxicity of ethanol on the yeast. Increasing the levels of the C0₂/ethanol treatment (1,0 atm.), showed a synergistic effect on yeast performance. The results of this study indicate that both extracellular ethanol and carbon dioxide do appear to inhibit yeast performance and affect membrane fatty acid composition of the cells by inhibiting the synthesis of the respective fatty acid. This affect has a significant bearing on the general metabolism of the yeast cell.
- Full Text:
- Date Issued: 1993
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