Microcystis aeruginosa toxin: cell culture toxicity, hemolysis, and mutagenicity assays

A large-scale sustained fish kill in the St. Johns River, Florida: A complex consequence of cyanobacteria blooms

In the summer of 2010, a sustained multispecies fish kill, affecting primarily adult red drum (Sciaenops ocellatus) and Atlantic stingray (Dasyatis sabina), along with various baitfish such as menhaden (Brevoortia spp.) and shad (Dorosoma spp.), was documented for six weeks along 50 km of the Lower St. Johns River (LSJR), Florida. An Aphanizomenon flos-aquae bloom was present in the freshwater reaches before the fish kill. The kill was triggered by a significant reverse-flow event and sudden influx of high-salinity water in late May that contributed to the collapse of the bloom upstream and brought euryhaline fish downstream into the vicinity of the senescing bloom or its by-products. The decomposing bloom led to a sequence of events, including the release of small amounts of cyanotoxins, bacterial lysis of cyanobacterial cells, high organic loading, and changes in the diversity and dominance of the plankton community to include Microcystis spp., Leptolyngbya sp., Pseudanabaena spp., Planktolyngbya spp., and low concentrations of Heterosigma akashiwo. Dissolved oxygen levels were within normal ranges in the reach of the fish kill, although elevated ammonia concentrations and high pH were detected farther upstream. These conditions resulted in complex pathological changes in fish that were not consistent with acute cyanotoxin exposure or with poor water quality but were attributable to chronic lethal hemolysis. Potential sources of hemolytic activity included H. akashiwo, Microcystis spp., and Bacillus cereus, a hemolytic bacterium. The continued presence of A. flos-aquae in the LSJR could have significant environmental repercussions and ideally the causal factors contributing to bloom growth and maintenance should be fully understood and managed.

Transport and retention of Microcystis aeruginosa in porous media: Impacts of ionic strength, flow rate, media size and pre-oxidization

Due to the climate change and human activity, the frequency and intensity of algal blooms have increased significantly. Recent studies have shown that during the bloom event, evaluated levels of cyanobacteria could infiltrate the drinking water treatment process and emerge in the filtered and disinfected water, thus threatening the safety of the drinking water supply. Among these concerned cyanobacteria, Microcystis aeruginosa is one of the most commonly detected species that cause algal bloom in a fresh water body. The present work was designed to investigate the transport and retention behaviour of Microcystis aeruginosa in a packed column to resolve the mechanisms that drive the transport behaviour of Microcystis under various operational conditions. The results showed that lab-cultured Microcystis aeruginosa could effectively break through the packed column regardless of ionic strength, media size or flow rate, as well as the presence of dissolved organic matter in the water under the conditions investigated. Such behaviour significantly contradicts those of fluorescent microspheres, which are commonly considered as ideal colloids. In addition, the combined impacts of pre-oxidation technologies and filtration on Microcystis aeruginosa removal were tested systematically. It was found that even the cells have been lysed/oxidized, no significant improvement of cell removals were observed in packed column. This paper provides a significant and comprehensive record of transport and retention behaviour of Microcystis aeruginosa in porous media. The results found herein suggest that in addition to the effort preventing toxin release/exposure during bloom events in source water, engineers and researchers should also pay attention to the transport and retention of Microcystis aeruginosa and other algal cells in filters to minimize the risk of breakthrough of cyanobacteria cells in the drinking water treatment process.

Microcystin-LR Induced Immunotoxicity in Mammals

Microcystins are toxic molecules produced by cyanobacterial blooms due to water eutrophication. Exposure to microcystins is a global health problem because of its association with various other pathological effects and people all over the world are exposed to microcystins on a regular basis. Evidence shows that microcystin-LR (MC-LR) may adversely affect the immune system, but its specific effects on immune functions are lacking. In the present review, immunotoxicological effects associated with MC-LR in animals, humans, and in vitro models have been reported. Overall, the data shows that chronic exposure to MC-LR has the potential to impair vital immune responses which could lead to increased risk of various diseases including cancers. Studies in animal and in vitro models have provided some pivotal understanding into the potential mechanisms of MC-LR related immunotoxicity suggesting that further investigation, particularly in humans, is required to better understand the relationship between development of disease and the MC-LR exposure.

Unraveling cyanobacteria ecology in wastewater treatment plants (WWTP)

Cyanobacteria may be important components of wastewater treatment plants' (WWTP) biological treatment, reaching levels of 100% of the total phytoplankton density in some systems. The occurrence of cyanobacteria and their associated toxins in these systems present a risk to the aquatic environments and to public health, changing drastically the ecology of microbial communities and associated organisms. Many studies reveal that cyanotoxins, namely microcystins may not act as antibacterial compounds but they might have negative impacts on protozoans, inhibiting their growing and respiration rates and leading to changes in cellular morphology, decreasing consequently the treatment efficacy in WWTP. On the other side, flagellates and ciliates may ingest some cyanobacteria species while the formation of colonies by these prokaryotes may be seen as a defense mechanism against predation. Problems regarding the occurrence of cyanobacteria in WWTP are not limited to toxin production. Other cyanobacterial secondary metabolites may act as antibacterial compounds leading to the disruption of bacterial communities that biologically convert organic materials in WWTP being fundamental to the efficacy of the process. Studies reveal that the potential antibacterial capacity differs according to cyanobacteria specie and it seems to be more effective in Gram (+) bacteria. Thus, to understand the effects of cyanobacterial communities in the efficiency of the waste water treatment it will be necessary to unravel the complex interactions between cyanobacterial populations, bacteria, and protozoa in WWTP in situ studies.

Inhibition of nucleotide excision repair (NER) by microcystin-LR in CHO-K1 cells

Microcystin-LR (MC-LR), a potent inhibitor of PP1 and PP2A protein phosphatases, is related to tumor promotion and initiation. Although the genotoxic properties of this toxin have been extensively investigated with a variety of non-mammalian and mammalian test systems, the existing results are contradictory. Based on our previous results regarding the impact of MC-LR on the processes of DNA repair we decided to examine in greater detail its effect on the capacity of nucleotide excision repair (NER). CHO-K1 cells were pre-treated with increasing doses of MC-LR (1, 10 and 20 microg/ml) and then exposed to UV radiation (25 J/m(2)). Apoptosis was analyzed to exclude the possibility of false positive results in the comet assay. The results suggest that MC-LR targets the nucleotide excision repair mechanisms by interference with the incision/excision phase as well as the rejoining phase of NER and leads to an increased level of UV-induced cytogenetic DNA damage in CHO-K1 cells.

Damage of cell membrane and antioxidative system in human erythrocytes incubated with microcystin-LR in vitro

The effect of the exposure of human erythrocytes to different concentrations of microcystin-LR were studied. Lipid peroxidation, membrane fluidity, cell morphology, haemoglobin oxidation and changes in the activity of antioxidant enzymes were investigated. Human erythrocytes were incubated with microcystin-LR at concentrations of 1-1000 nM for 1, 6, 12 and 24 h. We observed that microcystin-LR induces a significant increase of the level of thiobarbituric acid reactive substances (TBARS), formation of echinocytes, haemolysis, conversion of oxyhaemoglobin to methaemoglobin, decrease of membrane fluidity on the level of 16 carbon atom fat acids. The compound also changed antioxidative enzymes activities: catalase, superoxide dismutase and glutathione reductase and formation of reactive oxygen species (ROS). All of the observed changes point out that 100 nM of Microcistin LR is the liminal (threshold) toxic dose for human erythrocytes. This dose caused most of the described changes. Observed damages of erythrocytes membrane and antioxidative enzymes may be the result of direct covalent binding of microcystin-LR with -SH residues of proteins and indirectly be related with reactive oxygen species formation.

Optimization of intracellular microcystin extraction for their subsequent analysis by high-performance liquid chromatography

Microcystins are a family of heptapeptide hepatotoxins produced by some genera of cyanobacteria. These toxins have been responsible for the illness and death of both animals and humans. Due to their hazard to human health, extraction of all intracellular microcystin variants is required to characterize and quantify all microcystins present in a sample. To date, there is little work reported comparing results obtained with different extraction methods. Findings reported to date indicate that selection of solvent will vary depending on sample and its microcystin contents. In the present work, a wide range of extraction volumes and solvents were evaluated over a range of pH and extraction times in order to optimize a suitable method for the extraction of a wide range of microcystins. The number of extractions required was also studied. This study was carried out using mainly two laboratory cultures which contain microcystin variants with quite different hydrophobicities. This is the first time that the most commonly used solvents for intracellular microcystin extraction have been studied in detail.

DNA damage and repair in human peripheral blood lymphocytes following treatment with microcystin-LR

The purpose of this study was to find a possible explanation of the inconsistency of data regarding the genotoxicity of microcystin-LR (MC-LR). We compared the results of the comet assay with the results of the analysis of chromosome aberrations and apoptosis. In order to investigate the influence of MC-LR on DNA damage in human lymphocytes, cells were treated with MC-LR at different concentrations (1, 10 and 25 microg/ml) for 6, 12, 18 and 24 h. Analyses of Olive Tail Moment (OTM) as an indicator of DNA damage showed that MC-LR treatment induced DNA damage in a time-dependent manner, reaching its maximum after 18 h. The lowest values of OTM were observed after 24 h. MC-LR had no effect on the frequency of chromosome aberrations in lymphocytes. Since some data available in the literature indicate that apoptosis may lead to overestimated or false positive results regarding the genotoxicity of mutagens in the comet assay, we measured the frequency of late apoptotic cells by use of the comet assay and the frequency of early apoptotic cells with the TUNEL method. The comet assay results revealed that the highest level of apoptosis was observed after 24 h and the lowest after 18 h. The comparison of the frequency of apoptotic cells determined by the comet assay with DNA damage (OTM) examined by the comet assay revealed a statistically significant, negative correlation. The TUNEL results showed that the frequency of apoptotic cells progressively increased in a dose- and time-dependent manner. The comparison of the frequency of apoptotic cells determined by TUNEL method with DNA damage (OTM) examined by the comet assay showed a significant positive correlation for lymphocytes treated with MC-LR for 6, 12 and 18 h. Therefore, our findings indicate that microcystin-LR-induced DNA damage observed in the comet assay may be related to the early stages of apoptosis due to cytotoxicity but not genotoxicity. In addition, we examined the DNA repair kinetics in lymphocytes following treatment with microcystin-LR and ionizing radiation. Our results indicate that MC-LR has an inhibiting effect on the repair of radiation-induced damage.

Genotoxicity of cyanobacterial extracts containing microcystins from Polish water reservoirs as determined by SOS chromotest and comet assay

Toxicity of cyanobacterial blooms, an increasing problem around the world, is connected to the increase in bloom samples containing microcystins, caused by excessive eutrophication of drinking- and recreational water reservoirs. Microcystins are the most common group of cyanobacterial hepatotoxins. In Poland they are produced mainly by the Microcystis genus. The toxicity of microcystins has been well documented, but investigation into their genotoxicity has been insufficient relative to the study of their overall toxicity. Therefore, the aim of this study was the estimation and comparison of the genotoxicity of cyanobacterial extracts with microcystins (CEMs) using the SOS chromotest (bacterial test) with Escherichia coli PQ37 and the comet assay with human lymphocytes. Cyanobacterial bloom samples were collected in the summer months from two Polish water reservoirs, one at Sulejów and one at Jeziorsko. The SOS chromotest, which used prokaryotic cells (without metabolic activation), and the comet assay, which used eukaryotic cells, both indicated the potential genotoxic effect of CEMs. Cyanobacterial extracts caused DNA damage in human lymphocytes in vitro. The maximum level of DNA damage was observed after 12 h incubation with CEMs. The bacterial test indicated a dependence of the degree of CEM genotoxicity, the composition, and the concentration of microcystins in each bloom sample examined with the time of exposure. Differences between the genotoxicity of cyanobacterial extract and the standard microcystin-LR were noticeable. This was probably caused by the interaction of different microcystin variants. The results showed that CEMs from Polish water reservoirs were genotoxic, which was reflected by the stimulation of the SOS repair system in bacterial cells (SOS chromotest) and by the damage induced in DNA in human lymphocytes (comet assay).

Purification of microcystins

Microcystins are an increasingly important group of bioactive compounds produced by a number of mainly planktonic cyanobacteria. They are a family of cyclic heptapeptides that cause both acute and chronic toxicity. Purified microcystins are utilised in a range of research applications including toxicological and biochemical studies, development of detection systems and the investigation of water treatment strategies. The commercial availability of purified microcystins is still relatively limited and for many projects the cost of their purchase prohibitive. The purification of microcystins from both bloom material and laboratory cultures is reviewed including a discussion on extraction, separation, and the determination of purity and yield.

Study on the cytotoxicity of microcystin-LR on cultured cells

The toxicity of purified blue-green algal toxin, microcystin-LR, on permanent cell lines KB, NIH/3T3, H-4-II-E, HeLa, Vero, Hep G2, Caco-2 and HL-60 was studied. Assessment of cell viability using colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays indicated that purified microcystin-LR induced toxic effect on KB and H-4-II-E cell lines after 96 h incubation at toxin concentrations greater than 18.75 microg/ml. KB cell line was selected for further study when reproducibility, consistency and sensitivity were considered. Significant amounts of lactate dehydrogenase (LDH) were released from KB cells when incubation durations were 72 and 96 h with toxin concentrations of 18.75 microg/ml and higher. Although previous studies suggested that microcystin-LR had no cytotoxic effect on permanent cell lines, LDH release assay performed on KB cells indicated that exposure to microcystin-LR could result in damage to the cell membrane.

Genotoxicity of microcystic cyanobacteria extract of a water source in China

The water pollution of toxic cyanobacteria (blue-green algae) is a worldwide problem and worsens with industrialization. Microcystins are potent cyclic heptapeptidic hepatotoxins produced mainly by Microcystis aeruginosa, and their hepatotoxicity has been well-documented. In contrast, information on the genotoxic effects of microcystins is relatively scarce. In our present study, the genotoxicity of microcystic cyanobacteria extract (MCE) of a water source in China was studied using Salmonella typhimurium assay (Ames test), comet assay (Single cell gel electrophoresis) and mouse micronucleus test. Results from Ames test indicated that MCE had strong mutagenicity regardless of the presence of S9. Moreover, MCE was able to induce DNA damage in primary cultured rat hepatocytes examined by comet assay. In addition, MCE also enhanced bone marrow micronucleated polychromatic erythrocytes in mice. The analysis of HPLC showed that the main component of MCE was microcystin-LR. The understanding of the potent genotoxicity of MCE will help to establish the possible link between water cyanobacteria contamination and high risk of primary liver cancer found in some endemic areas.

Liver slice culture for assessing hepatotoxicity of freshwater cyanobacteria

1. A modified mouse liver slice culture technique was established and the viability of the system was assessed on the basis of leakage of cytosolic enzymes viz. lactate dehydrogenase (LDH), alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartic aminotransferase (AST) and slice histology. 2. This system was employed for toxicity screening of five algal species of Indian origin on the basis of the EC50 for LDH leakage (dose of cyanobacteria resulting in leakage of 50% of enzyme) of a known toxic cyanobacterial strain Microcystis aeruginosa (PCC 7820). On the basis of both in vitro and in vivo toxicity none of the five species screened exhibited toxicity. 3. The toxicity of PCC 7820 was compared with a purified cyanobacterial hepatotoxin, Microcystin-LR. Various biochemical indices and histological changes confirm the hepatotoxic nature of the toxins. 4. The toxins did not induce glutathione-mediated lipid peroxidation but they did cause significant mitochondrial damage based on an MTT assay. 5. The study illustrates the utility of this in vitro system in identifying naturally occurring toxic cyanobacteria, particularly hepatotoxic species.

Cytotoxicity of cyanobacterium Microcystis aeruginosa

Cytotoxic effects of crude extracts and fractions of the purification steps towards Microcystin-LR (MCYST-LR) were investigated in vitro. Cytotoxicity was evaluated by measure of lactate dehydrogenase liberation of Chang liver cells and by hemolysis. Crude extracts of strain PCC 7806 damaged the cells within a few minutes. In contrast, MCYST-LR did not show any detectable cytotoxic effects. The cytotoxic activity could be related to a heat-labile substance with a molecular weight of about 30,000 Da.

Propagation of adenovirus types 40 and 41 in the PLC/PRF/5 primary liver carcinoma cell line

The sensitivity of cell cultures to adenovirus types 40 and 41 (Ad40/41) was compared by means of cell culture infectious dose (ID50) assays using monolayer cultures in microtitre plates. The PLC/PRF/5 cell line derived from a primary human hepatocellular carcinoma was 100 times more sensitive to a laboratory strain of Ad41, and 10 times more sensitive to a laboratory strain of Ad40 and two Ad41 stool isolates, than Graham 293 and Chang conjunctival cells commonly used for the propagation of these viruses. In microtitre plate titration assays PLC/PRF/5 cells retained an optimal condition for longer and displayed cytopathogenic effects earlier and more clearly than the other cell lines. In contrast to previously used cells, PLC/PRF/5 cells also proved successful for the quantitation of Ad41, but not Ad40, by conventional plaque assays. The reason for the exceptional susceptibility of PLC/PRF/5 cells has not been elucidated, but the findings open attractive new doors for research on Ad40/41.

Inhibitory effect of a toxic peptide isolated from a waterbloom of Microcystis sp. (Cyanobacteria) on iron uptake by rabbit reticulocytes

The effect of a soluble toxin purified from the algae bloom of a eutrophic lake dominated by Microcystis on the receptor-mediated endocytosis of ferro-transferrin in rabbit reticulocytes was studied. The toxin was a very effective inhibitor of cell iron uptake. Kinetic studies using 125I, 59Fe-labeled transferrin indicated that the step of ferrotransferrin internalization was selectively inhibited by the toxin while the surface receptor-binding capacity, the externalization of previously internalized transferrin, and the cellular ATP levels were not affected. These findings indicate that the reduction of iron uptake caused by the toxin is due to inhibition of the internalization of surface-located transferrin-transferrin receptor complexes, perhaps due to a disruption of cytoskeleton integrity.

Cell selective cytotoxicity of a peptide toxin from the cyanobacterium Microcystis aeruginosa

The effects of a cyclic peptide toxin, isolated from the cyanobacterium Microcystis aeruginosa, on cell morphology and ion transport in human erythrocytes, isolated rat hepatocytes and mouse fibroblasts (3T3) were studied. Neither in erythrocytes nor in fibroblasts did the toxin cause morphological alterations. In hepatocytes the toxin induced marked morphological alterations at a concentration of about 50 nM. In erythrocytes and fibroblasts no effects on ion transport were observed. In hepatocytes the toxin induced a significant increase in both phosphate and potassium efflux at concentrations far below the concentration causing morphological alterations (0.1 and 1 nM, respectively). It is suggested that the cytotoxicity of the toxin is not due to a non-specific interaction with the plasma membrane and that the effects of the toxin in hepatocytes are probably due to an interaction of the toxin with cytoskeletal elements.

Effects of the peptide toxin from Microcystis aeruginosa on intracellular calcium, pH and membrane integrity in mammalian cells

Extracts of water blooms of the toxic cyanobacterium Microcystis aeruginosa showed a range of toxicities not related to their ability to lyse mammalian red cells. The HPLC-purified heptapeptide toxin (mol. wt. 1035) from Microcystis did not lyse red cells at up to 500-fold higher concentrations than that required to kill mice. This toxin (LD50 110 micrograms/kg for male mice) was used to investigate in vitro effects on isolated thymocytes, hepatocytes, mammary alveolar cells, and cultured Swiss 3T3 fibroblasts. Thymocytes were stimulated to progressive Ca2+ entry by toxin (0.1-10 micrograms/ml), reaching a peak after approx. 5 min. No deformation, intracellular pH change, Trypan Blue entry or cell lysis was seen within 60 min at 37 degrees C. Hepatocytes were grossly deformed by the toxin, with a dose/response relationship between 0.1 and 1.0 microgram/ml. No progressive Ca2+ entry was observed on toxin addition, instead a rapid rise in intracellular Ca2+, presumably from intracellular sources. No change in intracellular pH, Trypan Blue exclusion or cell lysis was observed over 60 min. Mammary alveolar cells and 3T3 fibroblasts were unresponsive to toxin at the concentrations tested. No change in protein synthesis or nucleic acid synthesis in thymocytes was observed after culture with 0.5 or 5.0 micrograms/ml toxin. It was concluded that cytoskeletal changes in deformed hepatocytes (the target cells in vivo) demonstrated the most probable cellular basis for toxicity, rather than changes in membrane permeability or cell metabolism.

Use of freshly prepared rat hepatocytes to study toxicity of blooms of the blue-green algae Microcystis aeruginosa and Oscillatoria agardhii

Extracts from blue-green algal blooms (Microcystis aeruginosa and Oscillatoria agardhii) from different lakes in southeastern Norway were tested for toxicity toward freshly prepared rat hepatocytes. The toxicity effects were scored by means of morphological studies of the cells and by measuring leakage of the enzyme lactate dehydrogenase (LDH) from the cells. The results with the hepatocytes correspond well with results from the traditional mouse bioassay, concerning both ability to distinguish between toxic and nontoxic samples and estimation of relative toxicity. Morphological changes due to toxic effects on the plasma membrane appeared earlier than leakage of enzyme from damaged cells. The results indicate that the hepatocyte-toxicity assay system might be well suited for screening purposes concerning water contamination by blue-green algae.

Effects of Oscillatoria agardhii-toxins on blood pressure and isolated organ preparations

Toxic extracts of the blue-green alga Oscillatoria agardhii were tested for their effect on various isolated laboratory animal preparations. The Oscillatoria-toxins did not show hemagglutinative or hemolytical properties. An immediate rise in blood pressure was seen after intravenous injection in rats. As regards isolated organs, effects were most marked on the liver. Addition of toxic extract to isolated liver perfusion fluid led to physiological, biochemical and pathological changes indicating severe damage to the organ. Negative chronotropic and inotropic effects were found on the isolated heart. The toxins did not influence isolated smooth muscle or nerve striated muscle preparations.

Instability and variable toxicity of HBP-Tx, a toxin in the cyanobacterium Microcystis aeruginosa

It was found that autoxidative degradation is responsible for the inactivation of the unstable Microcystis toxin HBP-Tx. The purified toxin was similar in its properties to the "fast-death-factor" in Microcystis, described as a cyclic peptide in the literature. The apparent presence of an entirely different toxin was simulated by the partially inactivated HBP-Tx. A number of associated fluorescent compounds were identified as the non-toxic degradation products of the toxin. As a consequence, as established method for the detection of other algal toxins was applied. This chemical assay, which uses fluorescent measurement of the oxidized toxin in the cyanobacterium Aphanizomenon flos-aquae, was applicable for HBP-Tx after the removal of interfering degradation products of the toxin. The results obtained with Microcystis toxin HBP-Tx do not confirm suggestions concerning the structure of the "fast-death-factor".

Inactivation of hepatitis A virus and indicator organisms in water by free chlorine residuals

Hepatitis A virus (HAV) and selected indicator organisms were mixed together in chlorine-demand-free buffers at pH 6, 8, or 10 and exposed to free chlorine residuals, and the survival kinetics of individual organisms were compared. HAV was enumerated by a most-probable-number dilution assay, using PLC/PRF/5 liver cells for propagation of the virus and radioimmunoassay for its detection. At all pH levels, HAV was more sensitive than Mycobacterium fortuitum, coliphage V1 (representing a type of phage common in some sewage-polluted waters), and poliovirus type 2. Under certain conditions, HAV was more resistant than Escherichia coli, Streptococcus faecalis, coliphage MS2, and reovirus type 3. It was always more resistant than SA-11 rotavirus. Evidence is presented that conditions generally specified for the chlorine disinfection of drinking-water supplies will also successfully inactivate HAV and that HAV inactivation by free chlorine residuals can reliably be monitored by practical indicator systems consisting of appropriate combinations of suitable indicators such as coliform and acid-fast bacteria, coliphages, the standard plate count, and fecal streptococci.