Adsorption of the cyanobacterial hepatotoxin microcystin-LR by a low-cost activated carbon from the seed husks of the pan-tropical tree, Moringa oleifera

A low-cost activated carbon from the pan-tropical multipurpose tree Moringa oleifera removes the cyanobacterial hepatotoxin microcystin-LR in quantitative amounts from water in batch adsorption trials. The potential of M. oleifera seed husk carbon for cyanobacterial toxin removal in drinking water treatment in tropical countries is discussed.

Colorimetric protein phosphatase inhibition assay of laboratory strains and natural blooms of cyanobacteria: comparisons with high-performance liquid chromatographic analysis for microcystins

Microcystins are cyclic heptapeptide hepatotoxins commonly produced by bloom-forming genera of cyanobacteria. These toxins are potent and specific inhibitors of protein phosphatases 1 and 2A. We have optimised a rapid, simple and sensitive colorimetric protein phosphatase 1 inhibition assay, utilising the activity of protein phosphatase 1 as expressed in a recombinant strain of Escherichia coli, towards the chromogenic substrate, p-nitrophenyl phosphate. A standard curve for the inhibition of protein phosphatase 1 by microcystin-LR was constructed with an IC50 of about 38 ng ml-1 and a limit of detection of 10-20 ng ml-1. Twenty-three laboratory-grown strains and 25 natural bloom samples of cyanobacteria were analysed by high-performance liquid chromatography for microcystins and by the protein phosphatase 1 inhibition assay. Agreement for the microcystin contents of the samples detected by high-performance liquid chromatography and the protein phosphatase 1 inhibition assay showed good correlation (R2 > 0.93, P < 0.0001). The suitability of the colorimetric protein phosphatase 1 inhibition assay as a screen for cyanobacterial microcystins is discussed.

Degradation of the cyanobacterial hepatotoxin, nodularin, under light and dark conditions

The stability of the cyanobacterial hepatotoxin, nodularin, was determined during the incubation of purified toxin, and in nodularin-containing cell-free extracts and whole filaments of the nodularin-producer, Nodularia spumigena in sunlight and darkness. Levels of purified nodularin in aqueous solution remained approximately constant throughout the 9-day trials under all conditions, but decreased in cell-free extracts and whole filaments when incubated under all conditions, with losses being greatest in full sunlight, intermediate in sunlight minus ultraviolet wavelengths and lowest in continuous darkness. Photodegradation and detoxification in Artemia salina bioassays occurred when purified nodularin was irradiated with ultraviolet wavelengths using a laboratory lamp.

Cyanobacterial toxins: occurrence, modes of action, health effects and exposure routes

Cyanobacterial toxins are produced by terrestrial- fresh-, brackish- and sea-water cyanobacteria of cosmopolitan occurrence. These toxins present acute and chronic hazards to human and animal health and are responsible for isolated, sporadic animal fatalities (mammals, fish, birds) each year. Human health problems are associated with the ingestion of, and contact with cyanobacterial blooms and their toxins. Modes of action of cyanobacterial neurotoxins, hepatotoxins and skin irritants are considered. Recent indications of the accumulation of cyanobacterial toxins in fish, their effect on crop plants and their association with the deaths of human dialysis patients are discussed. These findings and events indicate an incomplete understanding of the exposure routes of these natural toxins and the need for greater awareness of their occurrence and properties among users of waterbodies which are prone to cyanobacterial bloom development.

Death of a dog attributed to the cyanobacterial (blue-green algal) hepatotoxin nodularin in South Africa

A bull terrier died after drinking water at the margin of Zeekoevlei near Cape Town. At the time, Zeekoevlei, a hypertrophic coastal lake, contained a bloom of the cyanobacteria Nodularia spumigena and Microcystis aeruginosa. The circumstances of the incident, clinical signs of poisoning and histopathology, which mainly revealed extensive liver damage, were consistent with cyanobacterial poisoning. The cyanobacterial bloom material contained 3.47 micrograms mg-1 dry weight of the pentapeptide hepatotoxin nodularin. It is inferred that the dog died of cyanobacterial hepatotoxicosis due to the ingestion of nodularin.

Pores formed in lipid bilayers and in native membranes by nodularin, a cyanobacterial toxin

Nodularin (NODLN), a cyclic pentapeptide hepatotoxin from the cyanobacterium Nodularia spumigena, induces pores in bilayers of diphytanoyl lecithin (DPhL) and in locust muscle membrane. NODLN increases the surface pressure of a DPhL monolayer; except when the surface pressure of the monolayer is high when the toxin causes a reduction of this parameter. NODLN pores exhibit many open conductance states; the higher state probabilities increasing when the transmembrane pressure is increased. The results from these studies are discussed in terms of two models for a NODLN pore, a torroidal model and a barrel-stave model. The edge energy of the NODLN pore of 1.4 x 10(-12) J/m is determined.

The role of protein phosphorylation in the assembly of a replication competent nucleus: investigations in Xenopus egg extracts using the cyanobacterial toxin microcystin-LR

Cell-free extracts of Xenopus eggs support nuclear assembly and DNA replication in vitro. Extracts supplemented with the protein phosphatase inhibitor microcystin-LR displayed various inhibitory effects at different concentrations of the toxin. In the presence of cycloheximide, additions of microcystin did not induce histone H1-kinase activity. Nevertheless, increasing concentrations of microcystin did sequentially prevent DNA replication, nuclear lamina assembly and nuclear envelope assembly. DNA replication was prevented when microcystin was added at 250 nM. Furthermore, this effect could be reversed after the addition of the catalytic sub-unit of protein phosphatase 2A to inhibited extracts. At a concentration of 250 nM microcystin, nuclear membrane assembly, nuclear lamina assembly and nuclear transport all occurred in egg extracts. In addition single-stranded M13 DNA replication was also permitted. However, it appeared that replicase assembly was not completed, since nuclei assembled in microcystin-treated extracts displayed an unusual distribution of proliferating cell nuclear antigen (PCNA). Although PCNA was located at sites that resembled pre-replication foci, this nuclear protein was readily solubilised when nuclei were isolated and extracted sequentially with Triton, nucleases and salts. Despite this, nuclei containing pre-assembled replication forks could synthesise DNA when transferred into microcystin-treated extracts.

Isolation and characterization of microcystins from laboratory cultures and environmental samples of Microcystis aeruginosa and from an associated animal toxicosis

Six microcystins were identified in a laboratory culture of the cyanobacterium (blue-green alga) Microcystis aeruginosa PCC 7813 using high-performance liquid chromatography coupled with diode array detection (HPLC-DAD) and mass spectrometry (LC-MS). The toxins were purified and further characterized by amino acid analysis and tandem mass spectrometry (MS-MS). The presence of the previously reported microcystin-LR and microcystin-LY was confirmed. Two further microcystins were characterized as microcystin-LW and microcystin-LF. Another two toxins were partially characterized and are believed to be an analog of microcystin-LR (molecular weight 1008) and microcystin-LM (molecular weight 969). Natural bloom material of M. aeruginosa collected from 2 reservoirs was found to have similar microcystin profiles using HPLC-DAD and LC-MS, indicating the widespread occurrence of these microcystin variants. In addition, the presence of 5 of the microcystins was confirmed in the rumen contents of a lamb by LC-MS and LC-MS-MS, providing the first report of microcystins identified in an animal suspected of being poisoned by cyanobacterial hepatotoxins.

Extraction and high-performance liquid chromatographic method for the determination of microcystins in raw and treated waters

Increasing concern over the presence of microcystins (cyanobacterial/blue-green algal hepatotoxins) in water supplies has emphasized the need for a suitable analytical method. As many microcystins are known to exist, a method was developed that permits the determination of numerous variants by a single procedure. The method involves filtration to separate cyanobacterial cells from water, allowing intracellular and extracellular toxin levels to be assessed. The cellular components of the samples are extracted repeatedly in methanol, which was found to be the most versatile solvent tested for the extraction of microcystins. The efficiency of this extraction procedure was found to be independent of cell biomass. The filtered water was subjected to trace enrichment using a C18 solid-phase extraction cartridge, followed by identification and determination by photodiode-array high-performance liquid chromatography. The procedure was assessed using four water samples (two raw and two treated) spiked with a mixture of five microcystins and the cyanobacterial hepatotoxin nodularin. Recoveries of all but one microcystin were found to be good when spiked with concentrations as low as 250 ng l-1. The linearity and precision of the experimental procedure were assessed for five microcystins and nodularin. The proposed method permits rapid sample processing and determination of several microcystins.

Mass mortality of common dolphins (Delphinus delphis) in south west England due to incidental capture in fishing gear

In the first quarter of 1992, 118 dolphin carcases, of which 54 were positively identified as common dolphins (Delphinus delphis), were found stranded on the coast of Cornwall and Devon. To determine the cause, detailed post mortem examinations were carried out on 38 of the carcases, and the results were compared with those from 20 common dolphins that stranded on the coast of Cornwall and Devon in the previous 15 months. There was no evidence that the deaths were due to an infectious or parasitic disease, or acute intoxication by any of the algal toxins, trace metals or chlorinated hydrocarbons measured. However, 30 of the 38 dolphins showed signs associated with incidental capture in fishing gear. Skin lesions characteristic of capture in a small-meshed net and the predominance of recently ingested Atlantic mackerel (Scomber scombrus) and pilchard (Sardina pilchardus) in the stomachs of the dolphins suggested that they had been caught in the trawl or purse seine nets used for these fish. There is insufficient information to explain why this high mortality occurred in 1992 and not in other years.

Uptake of cobalt and cesium by microalgal- and cyanobacterial-clay mixtures

Accumulation of cobalt and cesium by the microalga Scenedesmus obliquus and the cyanobacterium Synechocystis PCC 6803 has been characterized at metal concentrations ranging from 1-100 µM in the presence of three clay minerals, montmorillonite, illite, and kaolinite. The majority of metal uptake over a 4 h period consisted of rapid binding to the clay mineral-cell aggregates, and was unaffected by incubation in the dark or by the presence of the metabolic inhibitor carbonyl cyanide-3-chlorophenyl hydrazone (CCCP). This was followed by a slower, energy-dependent uptake of metal by the cell components of the mixtures, which was inhibited by incubation in the dark or in the presence of CCCP. The initial phase of uptake by the clay mineral-cell mixtures and mixture components alone conformed to a Freundlich adsorption isotherm, the order of uptake for both cobalt and cesium being montmorillonite-cells > illite-cells > kaolinite-cells. S. obliquus-clay mineral mixtures accumulated more cobalt and cesium than Synechocystis PCC 6803-clay mineral mixtures. On a dry weight basis, clay minerals alone accumulated greater amounts of metals than clay mineral-cell mixtures, which accumulated more than the cells alone. However, when the same data was expressed as amount of metal adsorbed per unit surface area, S. obliquus, in most cases, adsorbed greater amounts of cobalt and cesium than the clay minerals or Synechocystis PCC 6803. As the proportion of clay in a cell-clay mineral mixture was increased, the amount of metal accumulated also increased. Reduced accumulation of cobalt and cesium by cell-clay mineral mixtures, exhibited by equal amounts of the individual components added together, indicated that the formation of clay-cell aggregates had masked some of the binding sites normally available to metal ions. Accumulation of cobalt and cesium by all clay mineral-cell mixtures was dependent on the external pH and NaCl concentration, and decreased with decreasing pH and increasing external NaCl concentration.

Identification of anatoxin-A in benthic cyanobacteria (blue-green algae) and in associated dog poisonings at Loch Insh, Scotland

Dog deaths occurred in 1990 and 1991 after the animals drank water containing blooms of benthic cyanobacteria along the shoreline of Loch Insh, Scotland. Signs of poisoning in the affected animals and the high neurotoxicity of bloom extracts in laboratory bioassays indicated acute poisoning due to cyanobacterial neurotoxin(s). The neurotoxic blooms consisted largely of benthic Oscillatoria species which were also observed in the stomach contents of the poisoned dogs. Stomach contents were also neurotoxic in bioassays with the same signs of poisoning as the Oscillatoria blooms. The cyanobacterial alkaloid neurotoxin anatoxin-a was identified in bloom extracts and poisoned dog stomach contents by high-performance liquid chromatography and gas chromatography-mass spectrometry. A species of benthic Oscillatoria has been isolated from the neurotoxic bloom material and shown to produce anatoxin-a in laboratory culture. These findings are the first to associate anatoxin-a toxicoses with benthic, rather than planktonic, cyanobacteria. Procedures for anatoxin-a extraction and identification from the blooms and animal material are also detailed.

Caesium accumulation and interactions with other monovalent cations in the cyanobacterium Synechocystis PCC 6803

Growth of Synechocystis PCC 6803 in BG-11 medium supplemented with 1 mM-CsCl resulted in intracellular accumulation of Cs+ to a final level of approximately 510 nmol (109 cells)-1 after incubation for 10 d. The doubling time was increased by 64% and the final cell yield was decreased by 70% during growth in the presence of Cs+ as compared to growth in control BG-11 medium. When the total monovalent cation concentration of the medium was doubled by adding either K+ or Na+, levels of accumulated Cs+ were decreased by approximately 50% to 220 and 270 nmol (109 cells)-1, respectively, after 28 d with little inhibition of growth being apparent. Short-term experiments revealed that extracellular K+ and Na+ inhibited Cs+ accumulation to a similar extent, with 90% inhibition of Cs+ accumulation occurring at the highest concentrations used (50 mM-K+ or Na+; 1 mM-Cs+). In all experiments, Cs+ accumulation resulted in a reduction in intracellular K+, except when cells were grown in K+-depleted medium, although a stoichiometric relationship was not apparent, the amount of Cs+ accumulated generally being greater than the amount of K+ released. Cs+ accumulation had no discernible effect on intracellular Na+. When K+, Na+, Rb+, Li+ or Tl+ were supplied at equimolar (1 mM) concentrations to Cs+, only Tl+ significantly reduced Cs+ accumulation. However, an approximately 50% inhibition of Cs+ accumulation resulted when concentrations of K+, Na+, Rb+ or Li+ were increased to 10 mM, which suggests that Cs+ may have a higher affinity for the monovalent cation transport system than K+, Rb+ and TI+ also caused a decrease in intracellular K+, whereas Na+ and Li+ stimulated K+ uptake. Cs+ accumulation was dependent on the external Cs+ concentration and showed a linear relationship to external Cs+ concentrations≤2 mM over 12 h incubation. However, prolonged incubation in external Cs+ concentrations≥ 0·8 mM resulted in Cs+ release from the cells and after 48 h, similar amounts of Cs+ and K+ were present in cells incubated at these higher concentrations. Cs+ accumulation was energy- and pH-dependent. Incubation in the light at 4 °C, or in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), or at 22 °C in the dark resulted in decreased Cs+ accumulation and decreased K+ release from the cells. Increased amounts of Cs+ were accumulated as the pH of the external medium was increased, with maximal accumulation [approximately 1330 nmol Cs+ (109 cells)-1 after 24 h incubation] occurring at pH 10, the highest pH value used. It is suggested that an important mechanism of Cs+ toxicity in Synechocystis PCC 6803 arises through replacement of cellular K+ by Cs+. The possible role of primary producers such as cyanobacteria in the mobilization of this radionuclide in aquatic habitats is discussed.