Beta-N-methylamino-L-alanine in South African fresh water cyanobacteria : incidence, prevalence, ecotoxicological considerations and human exposure risk
- Authors: Esterhuizen-Londt, Maranda
- Date: 2010
- Subjects: Cyanobacteria , Bioaccumulation , Chromatographic analysis , Neurotoxic agents
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10306 , http://hdl.handle.net/10948/1473 , Cyanobacteria , Bioaccumulation , Chromatographic analysis , Neurotoxic agents
- Description: β-N-methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid associated with human neurodegenerative disease. Due to the cosmopolitan nature of cyanobacteria, detection of BMAA in cyanobacteria has caused concerns about human exposure risk. This study was therefore based on the hypothesis that BMAA poses a health risk to humans either by direct ingestion or by indirect exposure to BMAA from a cyanobacterial source via a freshwater food chain. A validated gas chromatography-mass spectrometry (GC-MS) BMAA analysis method and a confirmatory liquid chromatography-mass spectrometry (LC-MS) method, with improved sensitivity, were developed in addition to a LC-MS/MS method for analyte confirmation. These methods were used to quantify BMAA in South African cyanobacteria, isolated from various potable water reservoirs. The majority of the isolates tested, contained BMAA. Possible human exposure by direct consumption of BMAA released from cyanobacterial blooms was investigated by the development of a robust solid phase extraction (SPE) method used for BMAA concentration and quantification in raw and treated tap water. Despite the use of the SPE method that facilitated the concentration of BMAA from large quantities of water, no free dissolved BMAA was detected in raw or processed fresh water. The fate of exogenous BMAA was therefore investigated firstly by evaluating the efficacy of standard water treatment processes employed in South Africa and secondly by investigating the possibility of BMAA bioaccumulation and biomagnification in aquatic food chains. Standard water treatment processes proved highly efficient at removing free dissolved BMAA, explaining the absence of BMAA in treated tap water. However, the cause of the BMAA absence in raw potable water remained unknown. Uptake of BMAA by model aquatic organisms was investigated in controlled experiments. BMAA uptake was documented in both Ceratophyllum demersum and Daphnia magna, however, BMAA-protein association and biomagnification were not observed in D. magna. BMAA had an inhibitory effect on the oxidative stress enzyme acitivties of both organisms tested (as well as human S9 extracts), resulting in accumulation of detrimental reactive oxygen species (ROS) in the cells. Exposure of crop plants to BMAA in controlled experiments resulted in BMAA uptake, protein association, and subsequent inhibition of the antioxidative enzyme activities. However, BMAA was detected in neither free nor protein-associated form in natural crop plants irrigated with known BMAA-containing bloom water. Post-mortem liver samples of Clarias gariepinus (Catfish) and Crocodylus niloticus (Crocodile), from a natural fresh water ecosystem that experienced frequent cyanobacterial blooms, contained both free and protein-associated BMAA. Higher BMAA concentrations were found in crocodile liver samples compared to fish liver samples, strongly suggesting biomagnification from one trophic level to the next. BMAA concentrations corresponded to crocodile age. This is the first report of bioaccumulation and biomagnification in two trophic levels in a fresh water ecosystem. These findings strongly suggest possible human exposure via aquatic food chains of cyanobacterial origin. Direct BMAA exposure via drinking water is not plausible due to the efficiency of standard water treatment processes to remove BMAA. The use of raw water for agricultural and recreational use, however, remains a problem. The development of management strategies as well as daily tolerable levels for BMAA is urgently required.
- Full Text:
- Date Issued: 2010
- Authors: Esterhuizen-Londt, Maranda
- Date: 2010
- Subjects: Cyanobacteria , Bioaccumulation , Chromatographic analysis , Neurotoxic agents
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10306 , http://hdl.handle.net/10948/1473 , Cyanobacteria , Bioaccumulation , Chromatographic analysis , Neurotoxic agents
- Description: β-N-methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid associated with human neurodegenerative disease. Due to the cosmopolitan nature of cyanobacteria, detection of BMAA in cyanobacteria has caused concerns about human exposure risk. This study was therefore based on the hypothesis that BMAA poses a health risk to humans either by direct ingestion or by indirect exposure to BMAA from a cyanobacterial source via a freshwater food chain. A validated gas chromatography-mass spectrometry (GC-MS) BMAA analysis method and a confirmatory liquid chromatography-mass spectrometry (LC-MS) method, with improved sensitivity, were developed in addition to a LC-MS/MS method for analyte confirmation. These methods were used to quantify BMAA in South African cyanobacteria, isolated from various potable water reservoirs. The majority of the isolates tested, contained BMAA. Possible human exposure by direct consumption of BMAA released from cyanobacterial blooms was investigated by the development of a robust solid phase extraction (SPE) method used for BMAA concentration and quantification in raw and treated tap water. Despite the use of the SPE method that facilitated the concentration of BMAA from large quantities of water, no free dissolved BMAA was detected in raw or processed fresh water. The fate of exogenous BMAA was therefore investigated firstly by evaluating the efficacy of standard water treatment processes employed in South Africa and secondly by investigating the possibility of BMAA bioaccumulation and biomagnification in aquatic food chains. Standard water treatment processes proved highly efficient at removing free dissolved BMAA, explaining the absence of BMAA in treated tap water. However, the cause of the BMAA absence in raw potable water remained unknown. Uptake of BMAA by model aquatic organisms was investigated in controlled experiments. BMAA uptake was documented in both Ceratophyllum demersum and Daphnia magna, however, BMAA-protein association and biomagnification were not observed in D. magna. BMAA had an inhibitory effect on the oxidative stress enzyme acitivties of both organisms tested (as well as human S9 extracts), resulting in accumulation of detrimental reactive oxygen species (ROS) in the cells. Exposure of crop plants to BMAA in controlled experiments resulted in BMAA uptake, protein association, and subsequent inhibition of the antioxidative enzyme activities. However, BMAA was detected in neither free nor protein-associated form in natural crop plants irrigated with known BMAA-containing bloom water. Post-mortem liver samples of Clarias gariepinus (Catfish) and Crocodylus niloticus (Crocodile), from a natural fresh water ecosystem that experienced frequent cyanobacterial blooms, contained both free and protein-associated BMAA. Higher BMAA concentrations were found in crocodile liver samples compared to fish liver samples, strongly suggesting biomagnification from one trophic level to the next. BMAA concentrations corresponded to crocodile age. This is the first report of bioaccumulation and biomagnification in two trophic levels in a fresh water ecosystem. These findings strongly suggest possible human exposure via aquatic food chains of cyanobacterial origin. Direct BMAA exposure via drinking water is not plausible due to the efficiency of standard water treatment processes to remove BMAA. The use of raw water for agricultural and recreational use, however, remains a problem. The development of management strategies as well as daily tolerable levels for BMAA is urgently required.
- Full Text:
- Date Issued: 2010
Bioaccumulation and ecotoxicology of b-methylamino-l-alanine (BMAA) in model crop plants
- Niyonzima, Francois Niyongabo
- Authors: Niyonzima, Francois Niyongabo
- Date: 2010
- Subjects: Cyanobacteria , Environmental toxicology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10312 , http://hdl.handle.net/10948/1475 , Cyanobacteria , Environmental toxicology
- Description: Cyanobacteria are known to produce a variety of toxic compounds. β-N-methylamino-L-alanine (BMAA) is one of the neurotoxins produced by most cyanobacteria. BMAA has been implicated in amyotrophic lateral sclerosis / Parkinsonism dementia complex (ALS / PDC) and was suggested to contribute to this pathology after biomagnification and slow release of BMAA from a protein associated form. The uptake and accumulation of BMAA by the aquatic macrophyte Ceratophyllum demersum has recently been shown, but the consumption of aquatic macrophytes by humans is not typical. The uptake by, and accumulation in, crop plants (Nasturtium officinale and Daucus carota) was therefore investigated so as to establish the existence of any risk to humans from the consumption of plants irrigated with water from dams with high cyanobacterial biomass and therefore high BMAA levels. After the exposure to the BMAA through the growth medium, BMAA had no effect on growth and development of N. officinale and D. carota. The uptake and bioaccumulation of BMAA was observed in N. officinale and D. carota, and was found to be concentration-dependent. Both free and bound cellular BMAA was detected following BMAA exposure through the growth medium. The photosynthetic apparatus of N. officinale was not significantly damaged. The uptake and accumulation of BMAA in edible terrestrial plants may constitute another route of human exposure to BMAA; it may now be prudent to avoid spray irrigation of edible plants with waters from dams with high cyanobacterial biomass and therefore high BMAA levels. After uptake by plants, the cyanotoxins may induce oxidative stress. A recent study showed that BMAA has a significant inhibitory effect on the oxidative stress enzymes in C. demersum. Therefore, the toxicological effects on selected plants were investigated by a range of biochemical enzyme assays in order to establish the plant stress response to exogenous BMAA. The inhibition of antioxidant enzymes upon exposure of N. officinale to BMAA through the growth medium was observed. The inhibition of antioxidant defence enzymes by BMAA correlated with the BMAA bioaccumulation in N. officinale. Further investigations are needed to analyze the uptake, accumulation, and ecotoxicology of BMAA in other crop plants, and to examine the fate of BMAA in these plants particularly its distribution and metabolism.
- Full Text:
- Date Issued: 2010
- Authors: Niyonzima, Francois Niyongabo
- Date: 2010
- Subjects: Cyanobacteria , Environmental toxicology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10312 , http://hdl.handle.net/10948/1475 , Cyanobacteria , Environmental toxicology
- Description: Cyanobacteria are known to produce a variety of toxic compounds. β-N-methylamino-L-alanine (BMAA) is one of the neurotoxins produced by most cyanobacteria. BMAA has been implicated in amyotrophic lateral sclerosis / Parkinsonism dementia complex (ALS / PDC) and was suggested to contribute to this pathology after biomagnification and slow release of BMAA from a protein associated form. The uptake and accumulation of BMAA by the aquatic macrophyte Ceratophyllum demersum has recently been shown, but the consumption of aquatic macrophytes by humans is not typical. The uptake by, and accumulation in, crop plants (Nasturtium officinale and Daucus carota) was therefore investigated so as to establish the existence of any risk to humans from the consumption of plants irrigated with water from dams with high cyanobacterial biomass and therefore high BMAA levels. After the exposure to the BMAA through the growth medium, BMAA had no effect on growth and development of N. officinale and D. carota. The uptake and bioaccumulation of BMAA was observed in N. officinale and D. carota, and was found to be concentration-dependent. Both free and bound cellular BMAA was detected following BMAA exposure through the growth medium. The photosynthetic apparatus of N. officinale was not significantly damaged. The uptake and accumulation of BMAA in edible terrestrial plants may constitute another route of human exposure to BMAA; it may now be prudent to avoid spray irrigation of edible plants with waters from dams with high cyanobacterial biomass and therefore high BMAA levels. After uptake by plants, the cyanotoxins may induce oxidative stress. A recent study showed that BMAA has a significant inhibitory effect on the oxidative stress enzymes in C. demersum. Therefore, the toxicological effects on selected plants were investigated by a range of biochemical enzyme assays in order to establish the plant stress response to exogenous BMAA. The inhibition of antioxidant enzymes upon exposure of N. officinale to BMAA through the growth medium was observed. The inhibition of antioxidant defence enzymes by BMAA correlated with the BMAA bioaccumulation in N. officinale. Further investigations are needed to analyze the uptake, accumulation, and ecotoxicology of BMAA in other crop plants, and to examine the fate of BMAA in these plants particularly its distribution and metabolism.
- Full Text:
- Date Issued: 2010
Bioconditioning and nitrogen fertility effects of selected cyanobacteria strains on two degraded soils in the Eastern Cape Province, South Africa
- Authors: Maqubela, Mfundo Phakama
- Date: 2009
- Subjects: Nostoc , Cyanobacteria , Soil fertility -- Testing , Soils -- Nitrogen content , Cyanobacteria -- Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD (Soil Science)
- Identifier: vital:11959 , http://hdl.handle.net/10353/558 , Nostoc , Cyanobacteria , Soil fertility -- Testing , Soils -- Nitrogen content , Cyanobacteria -- Biotechnology
- Description: Some cyanobacteria strains have biofertilization and bioconditioning effects in soils. The objective of this study was to identify cyanobacteria with potential to improve the N fertility and structural stability of degraded soils and evaluate their effectiveness in soils of the Eastern Cape, South Africa. Isolation and characterization of the indigenous cyanobacteria strains with desirable properties was first to be undertaken because their effects are known to differ from strain to strain. Cyanobacteria strains 3g, 3v, and 7e were identified from 97 strains isolated from selected soils. Nostoc strains 3g and 3v had greater ability to produce exocellular polysaccharides (EPS) but low potential to fix atmospheric N2 (4.7 and 1.3 nmol C2H4 μg chl-1 h-1, respectively). On the other hand, strain 7e had the highest capability to fix atmospheric N2 (16.1 nmol C2H4 μg chl-1 h-1) but had the least ability to produce EPS. Evaluation of the strains was done in glasshouse studies starting with Nostoc strain 9v isolated from a Tanzanian soil, followed by the indigenous strains isolated from soils in Hertzog and Qunu, South Africa. Inoculation was done by uniformly applying cyanobacteria on the surface of potted soils at a rate of 6 g m-2. First harvest and soil sampling took place after six weeks, and the top 25 mm of the soil was mixed, replanted, and sampled again after a further six weeks (second harvest). Inoculation with Nostoc strain 9v increased soil N by 40 percent and 17 percent in Guquka and Hertzog soils, respectively, and consequently increased maize dry matter yields by 40 and 49 percent. Soil C increased by 27 percent and 8 percent in Guquka and Hertzog soils, respectively, and this increase was significantly associated with that of soil N (R2 = 0.838). Higher contents of soil C, soil N and mineral N, however, were found in non-cropped soils. Scanning Electron Microscopy (SEM) revealed coatings of EPS on soil particles and fragments of non-cropped inoculated soils, with iii other particles enmeshed in networks of filaments, in contrast to cropped and/or non-inoculated soils. The proportion of very stable aggregates was increased by inoculation but cropping with maize reduced the aggregate stability. Inoculating Hertzog soil with indigenous strains 3g and 7e increased the nitrate N in the first cropping by 49 percent and 69 percent respectively, in cropped soils. In the second cropping increases in mineral N were 41 percent and 43 percent in 3g and 7e inoculated soils, respectively. Maize dry matter yields were higher on inoculated soils both in the first and second harvest in response to the improved N status of the soil. Increases in aggregate MWD in cropped soil as determined by fast wetting, mechanical breakdown and slow wetting were 85 percent, 33 percent, 33 percent, respectively, for 3g inoculation, 64 percent, 41 percent, and 41 percent, respectively, for 7e inoculation and 60 percent, 24 percent, 50 percent for inoculation with 9v. In non-cropped soil, increases in MWD as determined by fast wetting, mechanical breakdown and slow wetting were 11 percent, 0 percent, 7 percent, respectively for 3g inoculation, 21 percent, 11 percent, and 7 percent, respectively for 7e inoculation, and 25 percent, 36 percent, and 19 percent for strain 9v inoculation. Scanning electron microscopy observations, which were confirmed by chemical results, revealed that inoculated soils had high EPS and filaments that encouraged soil aggregation and improved aggregate stability. Results of this study show that cyanobacteria strains isolated and selected for their ability to fix atmospheric N2 and produce EPS improved the fertility status and aggregate stability of degraded soils from South Africa.
- Full Text:
- Date Issued: 2009
- Authors: Maqubela, Mfundo Phakama
- Date: 2009
- Subjects: Nostoc , Cyanobacteria , Soil fertility -- Testing , Soils -- Nitrogen content , Cyanobacteria -- Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD (Soil Science)
- Identifier: vital:11959 , http://hdl.handle.net/10353/558 , Nostoc , Cyanobacteria , Soil fertility -- Testing , Soils -- Nitrogen content , Cyanobacteria -- Biotechnology
- Description: Some cyanobacteria strains have biofertilization and bioconditioning effects in soils. The objective of this study was to identify cyanobacteria with potential to improve the N fertility and structural stability of degraded soils and evaluate their effectiveness in soils of the Eastern Cape, South Africa. Isolation and characterization of the indigenous cyanobacteria strains with desirable properties was first to be undertaken because their effects are known to differ from strain to strain. Cyanobacteria strains 3g, 3v, and 7e were identified from 97 strains isolated from selected soils. Nostoc strains 3g and 3v had greater ability to produce exocellular polysaccharides (EPS) but low potential to fix atmospheric N2 (4.7 and 1.3 nmol C2H4 μg chl-1 h-1, respectively). On the other hand, strain 7e had the highest capability to fix atmospheric N2 (16.1 nmol C2H4 μg chl-1 h-1) but had the least ability to produce EPS. Evaluation of the strains was done in glasshouse studies starting with Nostoc strain 9v isolated from a Tanzanian soil, followed by the indigenous strains isolated from soils in Hertzog and Qunu, South Africa. Inoculation was done by uniformly applying cyanobacteria on the surface of potted soils at a rate of 6 g m-2. First harvest and soil sampling took place after six weeks, and the top 25 mm of the soil was mixed, replanted, and sampled again after a further six weeks (second harvest). Inoculation with Nostoc strain 9v increased soil N by 40 percent and 17 percent in Guquka and Hertzog soils, respectively, and consequently increased maize dry matter yields by 40 and 49 percent. Soil C increased by 27 percent and 8 percent in Guquka and Hertzog soils, respectively, and this increase was significantly associated with that of soil N (R2 = 0.838). Higher contents of soil C, soil N and mineral N, however, were found in non-cropped soils. Scanning Electron Microscopy (SEM) revealed coatings of EPS on soil particles and fragments of non-cropped inoculated soils, with iii other particles enmeshed in networks of filaments, in contrast to cropped and/or non-inoculated soils. The proportion of very stable aggregates was increased by inoculation but cropping with maize reduced the aggregate stability. Inoculating Hertzog soil with indigenous strains 3g and 7e increased the nitrate N in the first cropping by 49 percent and 69 percent respectively, in cropped soils. In the second cropping increases in mineral N were 41 percent and 43 percent in 3g and 7e inoculated soils, respectively. Maize dry matter yields were higher on inoculated soils both in the first and second harvest in response to the improved N status of the soil. Increases in aggregate MWD in cropped soil as determined by fast wetting, mechanical breakdown and slow wetting were 85 percent, 33 percent, 33 percent, respectively, for 3g inoculation, 64 percent, 41 percent, and 41 percent, respectively, for 7e inoculation and 60 percent, 24 percent, 50 percent for inoculation with 9v. In non-cropped soil, increases in MWD as determined by fast wetting, mechanical breakdown and slow wetting were 11 percent, 0 percent, 7 percent, respectively for 3g inoculation, 21 percent, 11 percent, and 7 percent, respectively for 7e inoculation, and 25 percent, 36 percent, and 19 percent for strain 9v inoculation. Scanning electron microscopy observations, which were confirmed by chemical results, revealed that inoculated soils had high EPS and filaments that encouraged soil aggregation and improved aggregate stability. Results of this study show that cyanobacteria strains isolated and selected for their ability to fix atmospheric N2 and produce EPS improved the fertility status and aggregate stability of degraded soils from South Africa.
- Full Text:
- Date Issued: 2009
Cyclodepsipeptides from a Kenyan marine cyanobacterium
- Authors: Dzeha, Thomas Mwambire
- Date: 2003
- Subjects: Cyanobacteria , Stereochemistry , Natural products -- Kenya
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4303 , http://hdl.handle.net/10962/d1004961 , Cyanobacteria , Stereochemistry , Natural products -- Kenya
- Description: An examination of an organic extract of the cyanobacterium Lyngbya majuscula collected from Wasini Island off the southern Kenyan coast led to the isolation of the known cyclodepsipeptide antanapeptin A (7), recently isolated from a Madagascan collection of L. majuscula, and a new bioactive cyclodepsipeptide, homodolastatin 16 (42). Although L. majuscula is a common, pantropical cyanobacterium this study represents the first investigation of the natural product chemistry of a Kenyan population of L. majuscula. The structures of the two cyclodepsipeptides were determined from 2D NMR and mass spectrometry data. The L- stereochemistry of the proline, valine, and N-methylphenylalanine amino acids in 7 and the L – proline configuration in 42, was confirmed by Marfey’s HPLC method. Chiral GC was used to determine the absolute stereochemistry of the hydroxyisovaleric acid moiety in 7 and 42, the lactate residue in 42 and tentatively propose an L-stereochemistry for the Nmethylisoleucine amino acid in 42. Homodolastatin 16, a higher homologue of the potential anti-cancer agent, dolastatin 16, exhibited moderate activity against two oesophageal cancer cell lines.
- Full Text:
- Date Issued: 2003
- Authors: Dzeha, Thomas Mwambire
- Date: 2003
- Subjects: Cyanobacteria , Stereochemistry , Natural products -- Kenya
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4303 , http://hdl.handle.net/10962/d1004961 , Cyanobacteria , Stereochemistry , Natural products -- Kenya
- Description: An examination of an organic extract of the cyanobacterium Lyngbya majuscula collected from Wasini Island off the southern Kenyan coast led to the isolation of the known cyclodepsipeptide antanapeptin A (7), recently isolated from a Madagascan collection of L. majuscula, and a new bioactive cyclodepsipeptide, homodolastatin 16 (42). Although L. majuscula is a common, pantropical cyanobacterium this study represents the first investigation of the natural product chemistry of a Kenyan population of L. majuscula. The structures of the two cyclodepsipeptides were determined from 2D NMR and mass spectrometry data. The L- stereochemistry of the proline, valine, and N-methylphenylalanine amino acids in 7 and the L – proline configuration in 42, was confirmed by Marfey’s HPLC method. Chiral GC was used to determine the absolute stereochemistry of the hydroxyisovaleric acid moiety in 7 and 42, the lactate residue in 42 and tentatively propose an L-stereochemistry for the Nmethylisoleucine amino acid in 42. Homodolastatin 16, a higher homologue of the potential anti-cancer agent, dolastatin 16, exhibited moderate activity against two oesophageal cancer cell lines.
- Full Text:
- Date Issued: 2003
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