An investigation into the role played by perceived security concerns in the adoption of mobile money services : a Zimbabwean case study
- Authors: Madebwe, Charles
- Date: 2015
- Subjects: Banks and banking, Mobile -- Zimbabwe , Global system for mobile communications , Cell phones -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4711 , http://hdl.handle.net/10962/d1017933
- Description: The ubiquitous nature of mobile phones and their popularity has led to opportunistic value added services (VAS), such as mobile money, riding on this phenomenon to be implemented. Several studies have been done to find factors that influence the adoption of mobile money and other information systems. The thesis looks at factors determining the uptake of mobile money over cellular networks with a special emphasis on aspects relating to perceived security even though other factors namely perceived usefulness, perceived ease of use, perceived trust and perceived cost were also looked at. The research further looks at the security threats introduced to mobile money by virtue of the nature, architecture, standards and protocols of Global System for Mobile Communications (GSM). The model employed for this research was the Technology Acceptance Model (TAM). Literature review was done on the security of GSM. Data was collected from a sample population around Harare, Zimbabwe using physical questionnaires. Statistical tests were performed on the collected data to find the significance of each construct to mobile money adoption. The research has found positive correlation between perceived security concerns and the adoption of money mobile money services over cellular networks. Perceived usefulness was found to be the most important factor in the adoption of mobile money. The research also found that customers need to trust the network service provider and the systems in use for them to adopt mobile money. Other factors driving consumer adoption were found to be perceived ease of use and perceived cost. The findings show that players who intend to introduce mobile money should strive to offer secure and useful systems that are trustworthy without making the service expensive or difficult to use. Literature review done showed that there is a possibility of compromising mobile money transactions done over GSM
- Full Text:
- Date Issued: 2015
- Authors: Madebwe, Charles
- Date: 2015
- Subjects: Banks and banking, Mobile -- Zimbabwe , Global system for mobile communications , Cell phones -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4711 , http://hdl.handle.net/10962/d1017933
- Description: The ubiquitous nature of mobile phones and their popularity has led to opportunistic value added services (VAS), such as mobile money, riding on this phenomenon to be implemented. Several studies have been done to find factors that influence the adoption of mobile money and other information systems. The thesis looks at factors determining the uptake of mobile money over cellular networks with a special emphasis on aspects relating to perceived security even though other factors namely perceived usefulness, perceived ease of use, perceived trust and perceived cost were also looked at. The research further looks at the security threats introduced to mobile money by virtue of the nature, architecture, standards and protocols of Global System for Mobile Communications (GSM). The model employed for this research was the Technology Acceptance Model (TAM). Literature review was done on the security of GSM. Data was collected from a sample population around Harare, Zimbabwe using physical questionnaires. Statistical tests were performed on the collected data to find the significance of each construct to mobile money adoption. The research has found positive correlation between perceived security concerns and the adoption of money mobile money services over cellular networks. Perceived usefulness was found to be the most important factor in the adoption of mobile money. The research also found that customers need to trust the network service provider and the systems in use for them to adopt mobile money. Other factors driving consumer adoption were found to be perceived ease of use and perceived cost. The findings show that players who intend to introduce mobile money should strive to offer secure and useful systems that are trustworthy without making the service expensive or difficult to use. Literature review done showed that there is a possibility of compromising mobile money transactions done over GSM
- Full Text:
- Date Issued: 2015
Correlation and comparative analysis of traffic across five network telescopes
- Nkhumeleni, Thizwilondi Moses
- Authors: Nkhumeleni, Thizwilondi Moses
- Date: 2014
- Subjects: Sensor networks , Computer networks , TCP/IP (Computer network protocol) , Computer networks -- Management , Electronic data processing -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4693 , http://hdl.handle.net/10962/d1011668 , Sensor networks , Computer networks , TCP/IP (Computer network protocol) , Computer networks -- Management , Electronic data processing -- Management
- Description: Monitoring unused IP address space by using network telescopes provides a favourable environment for researchers to study and detect malware, worms, denial of service and scanning activities. Research in the field of network telescopes has progressed over the past decade resulting in the development of an increased number of overlapping datasets. Rhodes University's network of telescope sensors has continued to grow with additional network telescopes being brought online. At the time of writing, Rhodes University has a distributed network of five relatively small /24 network telescopes. With five network telescope sensors, this research focuses on comparative and correlation analysis of traffic activity across the network of telescope sensors. To aid summarisation and visualisation techniques, time series' representing time-based traffic activity, are constructed. By employing an iterative experimental process of captured traffic, two natural categories of the five network telescopes are presented. Using the cross- and auto-correlation methods of time series analysis, moderate correlation of traffic activity was achieved between telescope sensors in each category. Weak to moderate correlation was calculated when comparing category A and category B network telescopes' datasets. Results were significantly improved by studying TCP traffic separately. Moderate to strong correlation coefficients in each category were calculated when using TCP traffic only. UDP traffic analysis showed weaker correlation between sensors, however the uniformity of ICMP traffic showed correlation of traffic activity across all sensors. The results confirmed the visual observation of traffic relativity in telescope sensors within the same category and quantitatively analysed the correlation of network telescopes' traffic activity.
- Full Text:
- Date Issued: 2014
- Authors: Nkhumeleni, Thizwilondi Moses
- Date: 2014
- Subjects: Sensor networks , Computer networks , TCP/IP (Computer network protocol) , Computer networks -- Management , Electronic data processing -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4693 , http://hdl.handle.net/10962/d1011668 , Sensor networks , Computer networks , TCP/IP (Computer network protocol) , Computer networks -- Management , Electronic data processing -- Management
- Description: Monitoring unused IP address space by using network telescopes provides a favourable environment for researchers to study and detect malware, worms, denial of service and scanning activities. Research in the field of network telescopes has progressed over the past decade resulting in the development of an increased number of overlapping datasets. Rhodes University's network of telescope sensors has continued to grow with additional network telescopes being brought online. At the time of writing, Rhodes University has a distributed network of five relatively small /24 network telescopes. With five network telescope sensors, this research focuses on comparative and correlation analysis of traffic activity across the network of telescope sensors. To aid summarisation and visualisation techniques, time series' representing time-based traffic activity, are constructed. By employing an iterative experimental process of captured traffic, two natural categories of the five network telescopes are presented. Using the cross- and auto-correlation methods of time series analysis, moderate correlation of traffic activity was achieved between telescope sensors in each category. Weak to moderate correlation was calculated when comparing category A and category B network telescopes' datasets. Results were significantly improved by studying TCP traffic separately. Moderate to strong correlation coefficients in each category were calculated when using TCP traffic only. UDP traffic analysis showed weaker correlation between sensors, however the uniformity of ICMP traffic showed correlation of traffic activity across all sensors. The results confirmed the visual observation of traffic relativity in telescope sensors within the same category and quantitatively analysed the correlation of network telescopes' traffic activity.
- Full Text:
- Date Issued: 2014
Exchange rates behaviour in Ghana and Nigeria: is there a misalignment?
- Authors: Mapenda, Rufaro
- Date: 2011 , 2011-11-09
- Subjects: Foreign exchange rates -- Ghana , Foreign exchange rates -- Nigeria , Economic development -- Ghana , Economic development -- Nigeria , Foreign exchange administration -- Ghana , Foreign exchange administration -- Nigeria , International relations
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:976 , http://hdl.handle.net/10962/d1002710 , Foreign exchange rates -- Ghana , Foreign exchange rates -- Nigeria , Economic development -- Ghana , Economic development -- Nigeria , Foreign exchange administration -- Ghana , Foreign exchange administration -- Nigeria , International relations
- Description: Exchange rates are believed to be one of the major driving forces behind sustainable macroeconomic growth and it is therefore important to ensure that they are at an appropriate level. Exchange rate misalignment is a situation where the actual exchange rate differs significantly from its equilibrium value, resulting in either an overvalued or an undervalued currency. The problem with an undervalued currency is that it will increase the domestic price of tradable goods whereas an overvalued currency will cause a fall in the domestic prices of the tradable goods. Persistent exchange rate misalignment is thus expected to result in severe macroeconomic instability. The aim of this study is to estimate the equilibrium real exchange rate for both Ghana and Nigeria. After so doing, the equilibrium real exchange rate is compared to the actual real exchange rate, in order to assess the extent of real exchange rate misalignment in both countries, if any such exists. In order test the applicability of the equilibrium exchange rate models, the study draws from the simple monetary model as well as the Edwards (1989) and Montiel (1999) models. These models postulate that the variables which determine the real exchange rate are the terms of trade, trade restrictions, domestic interest rates, foreign aid inflow, income, money supply, world inflation, government consumption expenditure, world interest rates, capital controls and technological progress. Due to data limitations in Ghana and in Nigeria, not all the variables are utilised in the study. The study uses the Johansen (1995) model as well as the Vector Error Correction Model (VECM) to estimate the long- and the short-run relationships between the above-mentioned determinants and the real exchange rate. Thereafter the study employs the Hodrick-Prescott filter to estimate the permanent equilibrium exchange rate. The study estimates a real exchange rate model each for Ghana and Nigeria. Both the exchange rate models for Ghana and Nigeria provide evidence of exchange rate misalignment. The model for Ghana shows that from the first quarter of 1980 to the last quarter of 1983 the real exchange rate was overvalued; thereafter the exchange rate moved close to its equilibrium value and was generally undervalued with few and short-lived episodes of overvaluation. In regard to real exchange rate misalignment in Nigeria prior to the Structural Adjustment Program in 1986 there were episodes of undervaluation from the first quarter of 1980 to the first quarter of 1984 and overvaluation from the second quarter of 1984 to the third quarter of 1986; thereafter the exchange rate was generally and marginally undervalued.
- Full Text:
- Date Issued: 2011
- Authors: Mapenda, Rufaro
- Date: 2011 , 2011-11-09
- Subjects: Foreign exchange rates -- Ghana , Foreign exchange rates -- Nigeria , Economic development -- Ghana , Economic development -- Nigeria , Foreign exchange administration -- Ghana , Foreign exchange administration -- Nigeria , International relations
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:976 , http://hdl.handle.net/10962/d1002710 , Foreign exchange rates -- Ghana , Foreign exchange rates -- Nigeria , Economic development -- Ghana , Economic development -- Nigeria , Foreign exchange administration -- Ghana , Foreign exchange administration -- Nigeria , International relations
- Description: Exchange rates are believed to be one of the major driving forces behind sustainable macroeconomic growth and it is therefore important to ensure that they are at an appropriate level. Exchange rate misalignment is a situation where the actual exchange rate differs significantly from its equilibrium value, resulting in either an overvalued or an undervalued currency. The problem with an undervalued currency is that it will increase the domestic price of tradable goods whereas an overvalued currency will cause a fall in the domestic prices of the tradable goods. Persistent exchange rate misalignment is thus expected to result in severe macroeconomic instability. The aim of this study is to estimate the equilibrium real exchange rate for both Ghana and Nigeria. After so doing, the equilibrium real exchange rate is compared to the actual real exchange rate, in order to assess the extent of real exchange rate misalignment in both countries, if any such exists. In order test the applicability of the equilibrium exchange rate models, the study draws from the simple monetary model as well as the Edwards (1989) and Montiel (1999) models. These models postulate that the variables which determine the real exchange rate are the terms of trade, trade restrictions, domestic interest rates, foreign aid inflow, income, money supply, world inflation, government consumption expenditure, world interest rates, capital controls and technological progress. Due to data limitations in Ghana and in Nigeria, not all the variables are utilised in the study. The study uses the Johansen (1995) model as well as the Vector Error Correction Model (VECM) to estimate the long- and the short-run relationships between the above-mentioned determinants and the real exchange rate. Thereafter the study employs the Hodrick-Prescott filter to estimate the permanent equilibrium exchange rate. The study estimates a real exchange rate model each for Ghana and Nigeria. Both the exchange rate models for Ghana and Nigeria provide evidence of exchange rate misalignment. The model for Ghana shows that from the first quarter of 1980 to the last quarter of 1983 the real exchange rate was overvalued; thereafter the exchange rate moved close to its equilibrium value and was generally undervalued with few and short-lived episodes of overvaluation. In regard to real exchange rate misalignment in Nigeria prior to the Structural Adjustment Program in 1986 there were episodes of undervaluation from the first quarter of 1980 to the first quarter of 1984 and overvaluation from the second quarter of 1984 to the third quarter of 1986; thereafter the exchange rate was generally and marginally undervalued.
- Full Text:
- Date Issued: 2011
The photophysical properties of low symmetry phthalocyanines in conjunction with quantum dots
- Authors: D'Souza, Sarah
- Date: 2011
- Subjects: Phthalocyanines , Photochemistry , Zinc , Quantum dots , Spectrum analysis , Nanoparticles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4331 , http://hdl.handle.net/10962/d1004992 , Phthalocyanines , Photochemistry , Zinc , Quantum dots , Spectrum analysis , Nanoparticles
- Description: he synthesis, extensive spectroscopic characterization and photophysical studies of low symmetry zinc phthalocyanine have been conducted. Comparisons have been made taking into consideration the influence of the solvent properties as well as substituent type and position. Photosensitizing properties of the zinc phthalocyanine derivatives in the presence of thiol capped CdTe quantum dots (QDs) were compared. The QDs were used as energy transfer donors and to facilitate with energy transfer through Förster resonance energy transfer (FRET) from the QDs to the MPcs. The linkage of unsymmetrically substituted 4-monoaminophenoxy zinc phthalocyanine (ZnAPPc) to CdTe quantum dots capped with mercaptopropionic acid (MPA), L-cysteine (L-cys) or thioglycolic acid (TGA) has been achieved using the coupling agents ethyl-N3 dimethylaminopropyl)carbodiimide (EDC) and N-hydroxy succinimide (NHS), which facilitate formation of an amide bond to form the QD-ZnAPPc-linked complex. The formation of the amide bond was confirmed using UV-Vis, Raman and IR spectroscopies, as well as AFM (atomic force microscopy). Förster resonance energy transfer (FRET) resulted in stimulated emission of ZnAPPc in both the linked (QDZnAPPc-linked) and mixed (QD:ZnAPPc-mixed) conjugates for MPA only. The linked L-cys and TGA complexes (QD-ZnAPPc-linked) gave the largest FRET efficiencies hence showing the advantages of covalent linking. Fluorescence quantum yields of QDs were decreased in QD:ZnAPPc-mixed and QD:ZnAPPc-linked. High triplet state quantum yields were obtained for the linked QD-phthalocyanine derivatives (ZnAPPc)and monoaminozinc phthalocyanine (ZnAPc) compared to when ZnAPPc and ZnAPc were mixed with MPA QDs without a chemical bond.
- Full Text:
- Date Issued: 2011
- Authors: D'Souza, Sarah
- Date: 2011
- Subjects: Phthalocyanines , Photochemistry , Zinc , Quantum dots , Spectrum analysis , Nanoparticles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4331 , http://hdl.handle.net/10962/d1004992 , Phthalocyanines , Photochemistry , Zinc , Quantum dots , Spectrum analysis , Nanoparticles
- Description: he synthesis, extensive spectroscopic characterization and photophysical studies of low symmetry zinc phthalocyanine have been conducted. Comparisons have been made taking into consideration the influence of the solvent properties as well as substituent type and position. Photosensitizing properties of the zinc phthalocyanine derivatives in the presence of thiol capped CdTe quantum dots (QDs) were compared. The QDs were used as energy transfer donors and to facilitate with energy transfer through Förster resonance energy transfer (FRET) from the QDs to the MPcs. The linkage of unsymmetrically substituted 4-monoaminophenoxy zinc phthalocyanine (ZnAPPc) to CdTe quantum dots capped with mercaptopropionic acid (MPA), L-cysteine (L-cys) or thioglycolic acid (TGA) has been achieved using the coupling agents ethyl-N3 dimethylaminopropyl)carbodiimide (EDC) and N-hydroxy succinimide (NHS), which facilitate formation of an amide bond to form the QD-ZnAPPc-linked complex. The formation of the amide bond was confirmed using UV-Vis, Raman and IR spectroscopies, as well as AFM (atomic force microscopy). Förster resonance energy transfer (FRET) resulted in stimulated emission of ZnAPPc in both the linked (QDZnAPPc-linked) and mixed (QD:ZnAPPc-mixed) conjugates for MPA only. The linked L-cys and TGA complexes (QD-ZnAPPc-linked) gave the largest FRET efficiencies hence showing the advantages of covalent linking. Fluorescence quantum yields of QDs were decreased in QD:ZnAPPc-mixed and QD:ZnAPPc-linked. High triplet state quantum yields were obtained for the linked QD-phthalocyanine derivatives (ZnAPPc)and monoaminozinc phthalocyanine (ZnAPc) compared to when ZnAPPc and ZnAPc were mixed with MPA QDs without a chemical bond.
- Full Text:
- Date Issued: 2011
Integration between the South African and international bond markets : implications for portfolio diversification
- Authors: Rabana, Phomolo
- Date: 2009
- Subjects: Bond market , Bond market -- South Africa , Principal components analysis , International finance , Foreign exchange rates -- South Africa , Investments -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:947 , http://hdl.handle.net/10962/d1002681 , Bond market , Bond market -- South Africa , Principal components analysis , International finance , Foreign exchange rates -- South Africa , Investments -- South Africa
- Description: International bond market linkages are examined using monthly bond yield data and total return indices on government bonds with ten years to maturity. The bond yield data covers a nineteen-year period from January 1990 to July 2008, while the bond total return index data covers a nine-year period from August 2000 to July 2008. The international bond markets included in the study are Australia, Canada, Germany, Japan, the United Kingdom, and the United States. The examination of international bond market linkages across these markets has important implications for the formulation of effective portfolio diversification strategies. The empirical analysis is carried out in three phases: the preliminary analysis, the principal component analysis (PCA), and the cointegration analysis. For each analysis and for each set of data the full sample period is first analysed and subsequently a five-year rolling window approach is implemented. Accordingly, this makes it possible to capture the time-varying nature of international bond market linkages. The preliminary analysis examines the bond market trends over the sample period, provides descriptive statistics, and reports the correlation coefficients between the selected bond markets. The PCA investigates the interrelationships among the bond markets according to their common sources of movement and identifies which markets tend to move together. The cointegration analysis is carried out using the Johansen cointegration procedure and investigates whether there is long-run comovement between South Africa and the selected bond markets. Where cointegration is found, Vector Error-Correction Models (VECMs) are estimated in order to examine the long-run equilibrium relationships in addition to their short-run adjustments over time. The empirical analysis results were robust, and overall integration between SA and the selected major bond markets remained weak and sporadic. In addition, the results showed that even after accounting for exchange rate differentials, international bond market diversification remained beneficial for a South African investor; and since international bond market linkages remained weak with no observable trend, international bond market diversification will remain beneficial for some time to come for a South African investor.
- Full Text:
- Date Issued: 2009
- Authors: Rabana, Phomolo
- Date: 2009
- Subjects: Bond market , Bond market -- South Africa , Principal components analysis , International finance , Foreign exchange rates -- South Africa , Investments -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:947 , http://hdl.handle.net/10962/d1002681 , Bond market , Bond market -- South Africa , Principal components analysis , International finance , Foreign exchange rates -- South Africa , Investments -- South Africa
- Description: International bond market linkages are examined using monthly bond yield data and total return indices on government bonds with ten years to maturity. The bond yield data covers a nineteen-year period from January 1990 to July 2008, while the bond total return index data covers a nine-year period from August 2000 to July 2008. The international bond markets included in the study are Australia, Canada, Germany, Japan, the United Kingdom, and the United States. The examination of international bond market linkages across these markets has important implications for the formulation of effective portfolio diversification strategies. The empirical analysis is carried out in three phases: the preliminary analysis, the principal component analysis (PCA), and the cointegration analysis. For each analysis and for each set of data the full sample period is first analysed and subsequently a five-year rolling window approach is implemented. Accordingly, this makes it possible to capture the time-varying nature of international bond market linkages. The preliminary analysis examines the bond market trends over the sample period, provides descriptive statistics, and reports the correlation coefficients between the selected bond markets. The PCA investigates the interrelationships among the bond markets according to their common sources of movement and identifies which markets tend to move together. The cointegration analysis is carried out using the Johansen cointegration procedure and investigates whether there is long-run comovement between South Africa and the selected bond markets. Where cointegration is found, Vector Error-Correction Models (VECMs) are estimated in order to examine the long-run equilibrium relationships in addition to their short-run adjustments over time. The empirical analysis results were robust, and overall integration between SA and the selected major bond markets remained weak and sporadic. In addition, the results showed that even after accounting for exchange rate differentials, international bond market diversification remained beneficial for a South African investor; and since international bond market linkages remained weak with no observable trend, international bond market diversification will remain beneficial for some time to come for a South African investor.
- Full Text:
- Date Issued: 2009
Euphausiid population structure and grazing in the Indian sector of the Antarctic Polar Frontal Zone, during austral autumn
- Bernard, Anthony Thomas Firth
- Authors: Bernard, Anthony Thomas Firth
- Date: 2005
- Subjects: Euphausiacea -- Antarctic Ocean , Euphausiacea -- Feeding and feeds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5913 , http://hdl.handle.net/10962/d1015960
- Description: The trophodynamics of the numerically dominant euphausiid species within a region of high mesoscale oceanographic variability in the southwest Indian sector of the Antarctic Polar Frontal Zone (PFZ) were investigated during the austral autumns April/May) of 2004 and 2005. During the 2004 survey, sub-surface (200 m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF) bisected the survey area into two distinct zones, the Sub- Antarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll-a (chl-a) biomass was typical for the region (< 25 mg chl-a m⁻²), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 to 3.1 ind m⁻³ and 0.1 to 8.1 mg dwt m⁻³, respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). The multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, (2) and restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. E. triacantha was found to have the highest daily ingestion rate ranging from 1 226.1 to 6 029.1 ng pigm ind⁻¹d⁻¹, while the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4 to 943.0 ng pigm ind⁻¹ d⁻¹). The total grazing impact of the selected euphausiids ranged from < 0.1 to 20.1 μg pigm m⁻²d⁻¹, corresponding to < 0.15 % of the areal chl-a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggested that phytoplankton represented a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements. A cyclonic cold-core eddy spawned from the region of the APF located in the southwest Indian sector of the PFZ was the dominant feature during the 2005 survey. The total areal chl-a biomass throughout the region was low, ranging between 5.6 and 11.4 mg chl-a m⁻², and was significantly higher within the core of the eddy compared to the surrounding waters (p < 0.05). RMT-8 and WP-2 total euphausiid abundance and biomass estimates were high, and ranged from 0.004 to 0.36 ind m⁻³ and 0.065 to 1.21 mg dwt m⁻³, and from 0.01 to 18.2 ind m⁻³ and 0.01 to 15.7 mg dwt m⁻³, respectively. A distinct spatial pattern in the euphausiid community was evident with the Antarctic species, Euphausia frigida, E. triacantha and E. superba predominating within the core of the eddy, while the PFZ waters were characterized by the sub-Antarctic species, E. longirostris, Stylocheiron maximum, Nematoscelis megalops and Thysanoessa gregaria. The eddy edge acted as a transition zone where species from both regions co-occurred. Within the survey area the combined ingestion rate of the six numerically dominant euphausiid species ranged between 0.02 and 5.31 μg pigm m⁻²d¹, which corresponded to a loss of between < 0.001 and 0.11 % of the available chl-a biomass. E. triacantha and juvenile T. macura were identified as the dominant grazers. There was no apparent spatial pattern in the grazing activity of the euphausiids within the region of investigation. The average daily rations of the euphausiids examined were < 2 % of their body carbon. The low daily ration of the euphausiids could be ascribed to the predominance of small picophytoplankton in the region of investigation, which are too small to be grazed efficiently by larger zooplankton. The marked spatial patterns in species composition and the elevated abundance and biomass of euphausiids, suggest that the mesoscale eddies contribute to the spatial and temporal heterogeneity of the planktonic community of the PFZ and may represent important foraging regions for many of the apex predators within the region.
- Full Text:
- Date Issued: 2005
- Authors: Bernard, Anthony Thomas Firth
- Date: 2005
- Subjects: Euphausiacea -- Antarctic Ocean , Euphausiacea -- Feeding and feeds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5913 , http://hdl.handle.net/10962/d1015960
- Description: The trophodynamics of the numerically dominant euphausiid species within a region of high mesoscale oceanographic variability in the southwest Indian sector of the Antarctic Polar Frontal Zone (PFZ) were investigated during the austral autumns April/May) of 2004 and 2005. During the 2004 survey, sub-surface (200 m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF) bisected the survey area into two distinct zones, the Sub- Antarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll-a (chl-a) biomass was typical for the region (< 25 mg chl-a m⁻²), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 to 3.1 ind m⁻³ and 0.1 to 8.1 mg dwt m⁻³, respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). The multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, (2) and restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. E. triacantha was found to have the highest daily ingestion rate ranging from 1 226.1 to 6 029.1 ng pigm ind⁻¹d⁻¹, while the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4 to 943.0 ng pigm ind⁻¹ d⁻¹). The total grazing impact of the selected euphausiids ranged from < 0.1 to 20.1 μg pigm m⁻²d⁻¹, corresponding to < 0.15 % of the areal chl-a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggested that phytoplankton represented a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements. A cyclonic cold-core eddy spawned from the region of the APF located in the southwest Indian sector of the PFZ was the dominant feature during the 2005 survey. The total areal chl-a biomass throughout the region was low, ranging between 5.6 and 11.4 mg chl-a m⁻², and was significantly higher within the core of the eddy compared to the surrounding waters (p < 0.05). RMT-8 and WP-2 total euphausiid abundance and biomass estimates were high, and ranged from 0.004 to 0.36 ind m⁻³ and 0.065 to 1.21 mg dwt m⁻³, and from 0.01 to 18.2 ind m⁻³ and 0.01 to 15.7 mg dwt m⁻³, respectively. A distinct spatial pattern in the euphausiid community was evident with the Antarctic species, Euphausia frigida, E. triacantha and E. superba predominating within the core of the eddy, while the PFZ waters were characterized by the sub-Antarctic species, E. longirostris, Stylocheiron maximum, Nematoscelis megalops and Thysanoessa gregaria. The eddy edge acted as a transition zone where species from both regions co-occurred. Within the survey area the combined ingestion rate of the six numerically dominant euphausiid species ranged between 0.02 and 5.31 μg pigm m⁻²d¹, which corresponded to a loss of between < 0.001 and 0.11 % of the available chl-a biomass. E. triacantha and juvenile T. macura were identified as the dominant grazers. There was no apparent spatial pattern in the grazing activity of the euphausiids within the region of investigation. The average daily rations of the euphausiids examined were < 2 % of their body carbon. The low daily ration of the euphausiids could be ascribed to the predominance of small picophytoplankton in the region of investigation, which are too small to be grazed efficiently by larger zooplankton. The marked spatial patterns in species composition and the elevated abundance and biomass of euphausiids, suggest that the mesoscale eddies contribute to the spatial and temporal heterogeneity of the planktonic community of the PFZ and may represent important foraging regions for many of the apex predators within the region.
- Full Text:
- Date Issued: 2005
Ammonia removal from water by ion exchange using South African and Zambian zeolite samples
- Authors: Mwale, Monica
- Date: 2000
- Subjects: Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5215 , http://hdl.handle.net/10962/d1005058 , Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Description: One problem of intensive fish culture systems is the progressive build-up of toxic wastes such as ammonia. The possibility of improving aquaculture water quality using two kinds of zeolite is discussed. Zeolites are alumino-silicates whose framework allows them to exchange cations. Ion exchange has been demonstrated to be competitive with other methods of ammonia removal due to the high selectivity for ammonia exhibited by zeolite materials. In this study an unknown Zambian zeolite (identified as laumontite by X-ray diffraction techniques) and Pratley clinoptilolite (a South African zeolite) were tested under laboratory conditions and in a fresh water recirculating system. Ammonia cation exchange capacities (CEC) and suitable application rates for efficient water treatment were determined using the batch and column ion exchange procedures. Estimated ammonia uptake, the most important criterion used to assess performance of zeolite filters was strongly influenced by zeolite type, particle size, pre-treatment, regeneration and ion exchange method used. Statistical analysis showed significant differences in average ammonia CEC values between clinoptilolite (14.94 mg g⁻¹) and laumontite (2.77 mg g⁻¹), with the former displaying a higher Na⁺ ® NH₄⁺ exchange rate especially in the early reaction stages. This difference accords with the higher purity of clinoptilolite, 47% as opposed to 4.7% for laumontite, which makes it a better zeolite for ammonium removal. CEC increased linearly as particle size of the clinoptilolite was reduced resulting in a linear regression model (y = 18.29 – 3.704 x; r² = 74%). Pre-treatment of clinoptilolite using 1N NaCl significantly improved the ammonia CEC of clinoptilolite. Overall performance of both the batch and column methods achieved after regeneration (18.3 mg g⁻¹) was 25% higher than the estimated CEC values (13.0 mg g⁻¹) for the unregenerated samples of clinoptilolite. Comparison of CEC estimates using Pratley clinoptilolite, showed that average batch CEC estimates were significantly lower than the column method estimates. The average ammonia CEC values estimated in a fresh water recirculating system (5.80 mg g⁻¹ and 4.12 mg g⁻¹ for the 0.7-1.0 and 1.0-1.4 mm particle sizes, respectively) were significantly lower than the column and batch estimates for the same particle sizes (P < 0.05). Some nitrite (NO₂) and nitrate (NO3) build up was experienced probably due to the growth of autotrophs in the filters. Mass balance of nitrogen (N) for the three treatments of the fish trial (0.7-1.0 mm, 1.0-1.4 mm and the control treatment that had no zeolite in the filter) indicated that less that 10% of the N was retained for growth. It was found that 60% of the NH₄-N present associated with the soluble N was available for absorption by the zeolite filter or biological nitrification and that a total of approximately 22% of NH₄-N available was absorbed by clinoptilolite. The results indicate that the rate of nitrification can be deductively estimated by allowing a zeolite filter to become a biological filter. It is concluded that water treatment by ion exchange using natural zeolites, provides a reliable and efficient method for ammonia removal and appears to be a viable supplementary water treatment method for fresh water systems.
- Full Text:
- Date Issued: 2000
- Authors: Mwale, Monica
- Date: 2000
- Subjects: Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5215 , http://hdl.handle.net/10962/d1005058 , Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Description: One problem of intensive fish culture systems is the progressive build-up of toxic wastes such as ammonia. The possibility of improving aquaculture water quality using two kinds of zeolite is discussed. Zeolites are alumino-silicates whose framework allows them to exchange cations. Ion exchange has been demonstrated to be competitive with other methods of ammonia removal due to the high selectivity for ammonia exhibited by zeolite materials. In this study an unknown Zambian zeolite (identified as laumontite by X-ray diffraction techniques) and Pratley clinoptilolite (a South African zeolite) were tested under laboratory conditions and in a fresh water recirculating system. Ammonia cation exchange capacities (CEC) and suitable application rates for efficient water treatment were determined using the batch and column ion exchange procedures. Estimated ammonia uptake, the most important criterion used to assess performance of zeolite filters was strongly influenced by zeolite type, particle size, pre-treatment, regeneration and ion exchange method used. Statistical analysis showed significant differences in average ammonia CEC values between clinoptilolite (14.94 mg g⁻¹) and laumontite (2.77 mg g⁻¹), with the former displaying a higher Na⁺ ® NH₄⁺ exchange rate especially in the early reaction stages. This difference accords with the higher purity of clinoptilolite, 47% as opposed to 4.7% for laumontite, which makes it a better zeolite for ammonium removal. CEC increased linearly as particle size of the clinoptilolite was reduced resulting in a linear regression model (y = 18.29 – 3.704 x; r² = 74%). Pre-treatment of clinoptilolite using 1N NaCl significantly improved the ammonia CEC of clinoptilolite. Overall performance of both the batch and column methods achieved after regeneration (18.3 mg g⁻¹) was 25% higher than the estimated CEC values (13.0 mg g⁻¹) for the unregenerated samples of clinoptilolite. Comparison of CEC estimates using Pratley clinoptilolite, showed that average batch CEC estimates were significantly lower than the column method estimates. The average ammonia CEC values estimated in a fresh water recirculating system (5.80 mg g⁻¹ and 4.12 mg g⁻¹ for the 0.7-1.0 and 1.0-1.4 mm particle sizes, respectively) were significantly lower than the column and batch estimates for the same particle sizes (P < 0.05). Some nitrite (NO₂) and nitrate (NO3) build up was experienced probably due to the growth of autotrophs in the filters. Mass balance of nitrogen (N) for the three treatments of the fish trial (0.7-1.0 mm, 1.0-1.4 mm and the control treatment that had no zeolite in the filter) indicated that less that 10% of the N was retained for growth. It was found that 60% of the NH₄-N present associated with the soluble N was available for absorption by the zeolite filter or biological nitrification and that a total of approximately 22% of NH₄-N available was absorbed by clinoptilolite. The results indicate that the rate of nitrification can be deductively estimated by allowing a zeolite filter to become a biological filter. It is concluded that water treatment by ion exchange using natural zeolites, provides a reliable and efficient method for ammonia removal and appears to be a viable supplementary water treatment method for fresh water systems.
- Full Text:
- Date Issued: 2000
Distributed authentication for resource control
- Authors: Burdis, Keith Robert
- Date: 2000
- Subjects: Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4630 , http://hdl.handle.net/10962/d1006512 , Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Description: This thesis examines distributed authentication in the process of controlling computing resources. We investigate user sign-on and two of the main authentication technologies that can be used to control a resource through authentication and providing additional security services. The problems with the existing sign-on scenario are that users have too much credential information to manage and are prompted for this information too often. Single Sign-On (SSO) is a viable solution to this problem if physical procedures are introduced to minimise the risks associated with its use. The Generic Security Services API (GSS-API) provides security services in a manner in- dependent of the environment in which these security services are used, encapsulating security functionality and insulating users from changes in security technology. The un- derlying security functionality is provided by GSS-API mechanisms. We developed the Secure Remote Password GSS-API Mechanism (SRPGM) to provide a mechanism that has low infrastructure requirements, is password-based and does not require the use of long-term asymmetric keys. We provide implementations of the Java GSS-API bindings and the LIPKEY and SRPGM GSS-API mechanisms. The Secure Authentication and Security Layer (SASL) provides security to connection- based Internet protocols. After finding deficiencies in existing SASL mechanisms we de- veloped the Secure Remote Password SASL mechanism (SRP-SASL) that provides strong password-based authentication and countermeasures against known attacks, while still be- ing simple and easy to implement. We provide implementations of the Java SASL binding and several SASL mechanisms, including SRP-SASL.
- Full Text:
- Date Issued: 2000
- Authors: Burdis, Keith Robert
- Date: 2000
- Subjects: Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4630 , http://hdl.handle.net/10962/d1006512 , Computers -- Access control , Data protection , Computer networks -- Security measures , Electronic data processing departments -- Security measures
- Description: This thesis examines distributed authentication in the process of controlling computing resources. We investigate user sign-on and two of the main authentication technologies that can be used to control a resource through authentication and providing additional security services. The problems with the existing sign-on scenario are that users have too much credential information to manage and are prompted for this information too often. Single Sign-On (SSO) is a viable solution to this problem if physical procedures are introduced to minimise the risks associated with its use. The Generic Security Services API (GSS-API) provides security services in a manner in- dependent of the environment in which these security services are used, encapsulating security functionality and insulating users from changes in security technology. The un- derlying security functionality is provided by GSS-API mechanisms. We developed the Secure Remote Password GSS-API Mechanism (SRPGM) to provide a mechanism that has low infrastructure requirements, is password-based and does not require the use of long-term asymmetric keys. We provide implementations of the Java GSS-API bindings and the LIPKEY and SRPGM GSS-API mechanisms. The Secure Authentication and Security Layer (SASL) provides security to connection- based Internet protocols. After finding deficiencies in existing SASL mechanisms we de- veloped the Secure Remote Password SASL mechanism (SRP-SASL) that provides strong password-based authentication and countermeasures against known attacks, while still be- ing simple and easy to implement. We provide implementations of the Java SASL binding and several SASL mechanisms, including SRP-SASL.
- Full Text:
- Date Issued: 2000
A distributed approach to surround sound production
- Authors: Smith, Adrian Wilfrid
- Date: 1999
- Subjects: Surround-sound systems , Computer sound processing , Music -- Data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4602 , http://hdl.handle.net/10962/d1004855 , Surround-sound systems , Computer sound processing , Music -- Data processing
- Description: The requirement for multi-channel surround sound in audio production applications is growing rapidly. Audio processing in these applications can be costly, particularly in multi-channel systems. A distributed approach is proposed for the development of a realtime spatialization system for surround sound music production, using Ambisonic surround sound methods. The latency in the system is analyzed, with a focus on the audio processing and network delays, in order to ascertain the feasibility of an enhanced, distributed real-time spatialization system.
- Full Text:
- Date Issued: 1999
- Authors: Smith, Adrian Wilfrid
- Date: 1999
- Subjects: Surround-sound systems , Computer sound processing , Music -- Data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4602 , http://hdl.handle.net/10962/d1004855 , Surround-sound systems , Computer sound processing , Music -- Data processing
- Description: The requirement for multi-channel surround sound in audio production applications is growing rapidly. Audio processing in these applications can be costly, particularly in multi-channel systems. A distributed approach is proposed for the development of a realtime spatialization system for surround sound music production, using Ambisonic surround sound methods. The latency in the system is analyzed, with a focus on the audio processing and network delays, in order to ascertain the feasibility of an enhanced, distributed real-time spatialization system.
- Full Text:
- Date Issued: 1999
Reproductive behaviour of the skunk clownfish, Amphiprion akallopisos, under captive conditions
- Authors: Haschick, Rory Dean
- Date: 1998
- Subjects: Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5316 , http://hdl.handle.net/10962/d1005161 , Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
- Description: The objectives of the study were to determine whether or not behaviour could be used to predict spawning in Amphiprion akallopisos, and to document the behaviour of this species under various environmental conditions in captivity. The spawning behaviour of A. akallopisos was studied and quantified. Three behaviour patterns - belly touching, nest cleaning by the female and mutual nest cleaning (by the male and the female) were identified as predictors for spawning. The reproductive behaviour of A.akallopisos under three photoperiods was investigated. The photoperiods were: 14L:10D, 10hr15minL:13hr45minD and a natural photoperiod cycle condensed into three months. A. akallopisos maintained under 14 L:10D exhibited a significantly higher frequency and duration of chasing, nest cleaning and total interaction compared to fish kept under 10hr15minL:13hr45minD. A photoperiod of 14L:10D was selected for further studies. As manipulation of photoperiod did not induce spawning, GnRHa was administered to the fish in the diet at levels of 10, 20, 40 and 80 μg/kg BW. Control groups were fed untreated food. None of the dosages were successful in inducing spawning, or spawning behaviour in A. akallopisos. It is possible that the method of hormone application was not suitable for this species. It is also possible that behaviour may regulate blood hormone levels as opposed to endocrine status influencing behaviour. In the third trial, A. akallopisos was maintained with, and without sea anemones in order to determine whether or not anemone hosts are necessary for spawning. The presence of anemones did not induce spawning and A. akallopisos kept without anemones exhibited significantly more interactive behaviour than fish kept with hosts. Spawning of A. akallopisos at a later date without anemones suggests that anemones are not necessary for spawning in A. akallopisos. Light intensity was investigated as a cue for spawning. The reproductive behaviour of A. akallopisos was then studied under light intensities of 4.16 x 10¹⁵ quanta.sec⁻¹.cm⁻², 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻² and this intensity plus natural light. Spawning occurred mainly under 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻². Fish maintained under this light intensity exhibited significantly more of nest cleaning behaviour in terms of frequency and duration than fish maintained under low light intensity. A minimum light intensity of 8.85 x 10¹⁵ quanta. sec⁻¹.cm⁻² is recommended for conditioning of this species. This study can be of practical relevance to hatchery managers who can use the methods developed and record predictors for spawning in A. akallopisos and other Amphiprion species. In this way imminence of spawning may be estimated. Most importantly, the study also has academic merit as little work has been undertaken in this field. Although the observational method used in this study was adequate for the purposes of the investigation, future work of this nature should incorporate other methods of documenting gonadal development such as gonadal staging and GSI in order to obtain more conclusive results.
- Full Text:
- Date Issued: 1998
- Authors: Haschick, Rory Dean
- Date: 1998
- Subjects: Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5316 , http://hdl.handle.net/10962/d1005161 , Anemonefishes -- Spawning , Amphiprion -- Reproduction , Fishes -- Reproduction , Hatchery fishes
- Description: The objectives of the study were to determine whether or not behaviour could be used to predict spawning in Amphiprion akallopisos, and to document the behaviour of this species under various environmental conditions in captivity. The spawning behaviour of A. akallopisos was studied and quantified. Three behaviour patterns - belly touching, nest cleaning by the female and mutual nest cleaning (by the male and the female) were identified as predictors for spawning. The reproductive behaviour of A.akallopisos under three photoperiods was investigated. The photoperiods were: 14L:10D, 10hr15minL:13hr45minD and a natural photoperiod cycle condensed into three months. A. akallopisos maintained under 14 L:10D exhibited a significantly higher frequency and duration of chasing, nest cleaning and total interaction compared to fish kept under 10hr15minL:13hr45minD. A photoperiod of 14L:10D was selected for further studies. As manipulation of photoperiod did not induce spawning, GnRHa was administered to the fish in the diet at levels of 10, 20, 40 and 80 μg/kg BW. Control groups were fed untreated food. None of the dosages were successful in inducing spawning, or spawning behaviour in A. akallopisos. It is possible that the method of hormone application was not suitable for this species. It is also possible that behaviour may regulate blood hormone levels as opposed to endocrine status influencing behaviour. In the third trial, A. akallopisos was maintained with, and without sea anemones in order to determine whether or not anemone hosts are necessary for spawning. The presence of anemones did not induce spawning and A. akallopisos kept without anemones exhibited significantly more interactive behaviour than fish kept with hosts. Spawning of A. akallopisos at a later date without anemones suggests that anemones are not necessary for spawning in A. akallopisos. Light intensity was investigated as a cue for spawning. The reproductive behaviour of A. akallopisos was then studied under light intensities of 4.16 x 10¹⁵ quanta.sec⁻¹.cm⁻², 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻² and this intensity plus natural light. Spawning occurred mainly under 8.85 x 10¹⁵ quanta.sec⁻¹.cm⁻². Fish maintained under this light intensity exhibited significantly more of nest cleaning behaviour in terms of frequency and duration than fish maintained under low light intensity. A minimum light intensity of 8.85 x 10¹⁵ quanta. sec⁻¹.cm⁻² is recommended for conditioning of this species. This study can be of practical relevance to hatchery managers who can use the methods developed and record predictors for spawning in A. akallopisos and other Amphiprion species. In this way imminence of spawning may be estimated. Most importantly, the study also has academic merit as little work has been undertaken in this field. Although the observational method used in this study was adequate for the purposes of the investigation, future work of this nature should incorporate other methods of documenting gonadal development such as gonadal staging and GSI in order to obtain more conclusive results.
- Full Text:
- Date Issued: 1998
Characterization and mode of action of a bacteriocin produced by a Bacteroides Fragilis strain
- Mossie, Godwin Mxolisi Kevin
- Authors: Mossie, Godwin Mxolisi Kevin
- Date: 1980
- Subjects: Bacteroides , Anaerobic bacteria , Trypsin , Dinitrophenol , Proteins -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4124 , http://hdl.handle.net/10962/d1013543
- Description: Bacteroides fragilis strain Bf-1 produces an extracellular bacteriocin at the beginning of the stationary growth phase. Production is not inducible by either ultraviolet light or mitomycin C. The low molecular weight bacteriocin (MW estimates of 13 500 and 18 800 obtained from Sephadex G-100 chromatography and SDS-PAGE electrophoresis respecively) is stable between pH 7 - 9 and is inactivated on incubation with trypsin and pronase. An unusual feature of the Bf-1 bacteriocin is its apparent biphasic temperature stability: while the majority of the activity (97%) is destroyed by heating at 60ºC (t [subscript] 1/2 = 2.5 min at 60ºC), a small proportion (3%) is stable even after autoclaving at 121ºC for 15 min. The killing of sensitive cells occurs in 2 stages and the killing action is reversed by incubation with trypsin. The transition from stage I to stage II is dependent on the temperature of incubation and the growth state of sensitive cells. 2,4-Dinitrophenol prevents this transition. The Bf-1 bacteriocin has an unusual mode of action. It specifically inhibits RNA synthesis whilst having no effect on protein or DNA synthesis. No effect on intracellular ATP levels were observed. The heat-stable (3%) fraction had a similar biochemical effect. In vitro studies involving RNA polymerase indicated that the bacteriocin and the antibiotic rifampicin have similar effects on RNA synthesis. The bacteriocinogenic strain (Bf-1) is insensitive to its own bacteriocin both in vivo and in vitro, although this immunity is overcome in vitro by the addition of higher concentrations of the Bf-1 bacteriocin. The bacteriocinogenic strain (Bf-1) harbors a cryptic plasmid (or plasmids) which on a neutral sucrose gradient, sediments faster than the Col E1 marker plasmid DNA. Attempts to cure this strain of its bacteriocinogenic phenotype were unsuccessful.
- Full Text:
- Date Issued: 1980
- Authors: Mossie, Godwin Mxolisi Kevin
- Date: 1980
- Subjects: Bacteroides , Anaerobic bacteria , Trypsin , Dinitrophenol , Proteins -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4124 , http://hdl.handle.net/10962/d1013543
- Description: Bacteroides fragilis strain Bf-1 produces an extracellular bacteriocin at the beginning of the stationary growth phase. Production is not inducible by either ultraviolet light or mitomycin C. The low molecular weight bacteriocin (MW estimates of 13 500 and 18 800 obtained from Sephadex G-100 chromatography and SDS-PAGE electrophoresis respecively) is stable between pH 7 - 9 and is inactivated on incubation with trypsin and pronase. An unusual feature of the Bf-1 bacteriocin is its apparent biphasic temperature stability: while the majority of the activity (97%) is destroyed by heating at 60ºC (t [subscript] 1/2 = 2.5 min at 60ºC), a small proportion (3%) is stable even after autoclaving at 121ºC for 15 min. The killing of sensitive cells occurs in 2 stages and the killing action is reversed by incubation with trypsin. The transition from stage I to stage II is dependent on the temperature of incubation and the growth state of sensitive cells. 2,4-Dinitrophenol prevents this transition. The Bf-1 bacteriocin has an unusual mode of action. It specifically inhibits RNA synthesis whilst having no effect on protein or DNA synthesis. No effect on intracellular ATP levels were observed. The heat-stable (3%) fraction had a similar biochemical effect. In vitro studies involving RNA polymerase indicated that the bacteriocin and the antibiotic rifampicin have similar effects on RNA synthesis. The bacteriocinogenic strain (Bf-1) is insensitive to its own bacteriocin both in vivo and in vitro, although this immunity is overcome in vitro by the addition of higher concentrations of the Bf-1 bacteriocin. The bacteriocinogenic strain (Bf-1) harbors a cryptic plasmid (or plasmids) which on a neutral sucrose gradient, sediments faster than the Col E1 marker plasmid DNA. Attempts to cure this strain of its bacteriocinogenic phenotype were unsuccessful.
- Full Text:
- Date Issued: 1980
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