Separation and identification of microcystins in cyanobacteria by frit-fast atom bombardment liquid chromatography/mass spectrometry

Cyanobacteria and cyanotoxins in the environment and water intakes: Reports, diversity of congeners, detection by mass spectrometry and their impact on health

Cyanobacteria are aquatic microorganisms of high interest for research due to the production of secondary metabolites, among which the most popular are cyanotoxins, responsible for causing severe poisoning in humans and animals through ingestion or contact with contaminated water bodies. Monitoring the number of cyanobacteria in water and concentrations of secreted cyanotoxins with the aid of sensitive and reliable methods is considered the primary action for evaluating potentially toxic blooms. There is a great diversity of methods to detect and identify these types of micro contaminants in water, differing by the degree of sophistication and information provided. Mass Spectrometry stands out for its accuracy and sensitivity in identifying toxins, making it possible to identify and characterize toxins produced by individual species of cyanobacteria, in low quantities. In this review, we seek to update some information about cyanobacterial peptides, their effects on biological systems, and the importance of the main Mass Spectrometry methods used for detection, extraction, identification and monitoring of cyanotoxins.

Time dependent uptake, bioaccumulation and biotransformation of cell free crude extract microcystins from Lake Amatitlán, Guatemala by Ceratophyllum demersum, Egeria densa and Hydrilla verticillata

Recent studies evidence that macrophytes can uptake and bioaccumulate microcystins (MC) from contaminated environments, suggesting their use in phytoremediation. In the present study Ceratophyllum demersum, Egeria densa and Hydrilla verticillata were exposed to cell free crude extracts (CE) containing three MC congeners MC-LR, MC-RR and MC-YR at a total MC concentration of 104.4 ± 7.6 μg/L from Lake Amatitlán, Guatemala. Time dependent total glutathione (tGSH), glutathione disulfide (GSSG), disappearance of MC from exposure medium and macrophyte uptake as well as calculated uptake and biotransformation rates and bioconcentration factors (BCF) were monitored after 1, 4, 8 hours (h) and 1, 3, 7 and 14 days (d). Results showed that tGSH concentrations in all exposed macrophytes were enhanced by CE. Disappearance of 62.1 ± 13, 40.8 ± 3.1 and 37.8 ± 3.5 μg/L total MCs from exposure mediums with E. densa, H. verticillata and C. demersum were observed after 1 h. Followed by the total elimination of MCs in exposure medium from H. verticillata after 14 d. Highest MC bioaccumulation capacity (BCF), was observed in E. densa followed by C. demersum and H. verticillata. The here presented results imply the strong MC phytoremediation potential of the evaluated macrophytes.

Toxic picoplanktonic cyanobacteria--review

Cyanobacteria of a picoplanktonic cell size (0.2 to 2.0 µm) are common organisms of both freshwater and marine ecosystems. However, due to their small size and relatively short study history, picoplanktonic cyanobacteria, in contrast to the microplanktonic cyanobacteria, still remains a poorly studied fraction of plankton. So far, only little information on picocyanobacteria toxicity has been reported, while the number of reports concerning their presence in ecosystems is increasing. Thus, the issue of picocyanobacteria toxicity needs more researchers' attention and interest. In this report, we present information on the current knowledge concerning the picocyanobacteria toxicity, as well as their harmfulness and problems they can cause.

Account: characterization and identification of microcystins by mass spectrometry

In this brief overview, the authors describe mass spectral techniques for the detection and identification of microcystin toxins. Microcystins are secondary metabolites produced by cyanobacteria. Determination of these toxic compounds and discovery of new variants is very important as they pose a great danger to the human food chain. Cyanobacterial blooms frequently occur in many areas worldwide and have the potential to contaminate the water via cyanotoxin release, especially microcystins. Among the various analytical techniques used for analysis, mass spectrometry has become the most important method as it allows simultaneous quantification and structural characterization of multiple microcystin variants. This brief overview article focuses on mass spectrometry techniques for identification of microcystins, including ionization methods, mass spectral fragmentation routes, profiling techniques, tandem and high-resolution mass spectrometry as well as typing of cyanobacterial strains.

Quantitative variations of intracellular microcystin-LR, -RR and -YR in samples collected from four locations in Hartbeespoort Dam in North West Province (South Africa) during the 2010/2011 summer season

The Hartbeespoort (HBP) Dam is a reservoir used for agricultural, domestic supply of raw potable water and recreational activities in South Africa’s North-West Province. Eutrophication and cyanobacterial blooms have long been a cause of water-quality problems in this reservoir. The most prevalent bloom-forming species is Microcystis aeruginosa, often producing the toxin microcystin, a hepatotoxin which can negatively impact aquatic animal and human health, and poses a problem for potable water supply. Algal samples were collected monthly from four pre-determined sites in the dam during the summer months (December 2010–March 2011). Intracellular microcystins (MCs) were extracted using SPE C₁₈ cartridges, followed by separation, identification and quantification using LC-ESI-MS techniques. Quantitative variation studies of MCs were conducted with respect to MC congener isolated, sampling site and month. Three main MC congeners (MC-RR, -LR and-YR) were isolated, identified and quantified. In addition, three minor MCs (MC-WR, MC-(H₄)YR and (D-Asp³, Dha⁷)MC-RR were also identified, but were not quantified. The MC dominance followed the order MC-RR>MC-LR>MC-YR across all sites and time. The maximum and minimum concentrations were 268 µg/g and 0.14 µg/g DW for MC-RR and MC-YR, respectively, of the total MCs quantified from this study. One-way ANOVA showed that there were no significant differences between average MC concentrations recorded across months (P = 0.62), there was, however, a marginally-significant difference in concentrations among MC congeners (P = 0.06). ANCOVA revealed a highly significant interaction between sites and MC congeners on MC concentration (P < 0.001).

Ms identification of microcystin-LR chlorination by-products

Drinking water disinfection by chlorine is known to reduce concentration of microcystin, but compounds formed are rarely considered. In this work the chlorination of microcystin-LR has been studied by monitoring reactants consumption and reaction products using the linear trap quad-Orbitrap (LTQ-Orbitrap) technology. Microcystin-LR was totally transformed within 2 min, meanwhile chlorine was consumed until 30 min with a rate of 12 mol per mol of toxin. Four new by-products of microcystin-LR were identified as well as their isomers: monochloro-microcystin, monochloro-dihydroxy-microcystin, dichloro-dihydroxy-microcystin and trichloro-hydroxy-microcystin. In addition, four new isomers were also observed, corresponding to the dihydroxy-microcystin already known. Besides, another compound previously observed was identified as monochloro-hydroxy-microcystin.

Cyanobacterial bioactive molecules — an overview of their toxic properties

Allelopathic interactions involving cyanobacteria are being increasingly explored for the pharmaceutical and environmental significance of the bioactive molecules. Among the toxic compounds produced by cyanobacteria, the biosynthetic pathways, regulatory mechanisms, and genes involved are well understood, in relation to biotoxins, whereas the cytotoxins are less investigated. A range of laboratory methods have been developed to detect and identify biotoxins in water as well as the causal organisms; these methods vary greatly in their degree of sophistication and the information they provide. Direct molecular probes are also available to detect and (or) differentiate toxic and nontoxic species from environmental samples. This review collates the information available on the diverse types of toxic bioactive molecules produced by cyanobacteria and provides pointers for effective exploitation of these biologically and industrially significant prokaryotes.

Liquid Chromatography−Tandem Mass Spectrometry Application, for the Determination of Extracellular Hepatotoxins in Irish Lake and Drinking Waters

A novel method for the determination of hepatotoxins; microcystins (MCs), and nodularin (Nod) in lake water and domestic chlorinated tap water has been developed using liquid chromatography hyphenated with electrospray ionization triple quadrupole mass spectrometry (LC-ESI-MS/MS). Optimization of the mass spectrometer parameters and mobile-phase composition was performed to maximize the sensitivity and reproducibility of the method. Detection of the hepatotoxins was carried out using multiple reaction monitoring experiments, thus improving the selectivity of the method. A total ion chromatogram and a precursor ion scan on ion m/z 135 was also applied to all samples to detect unknown microcystins or microcystins for which there are no standards available. A comprehensive validation of the LC-ESI-MS/MS method was completed that took into account matrix effects, specificity, linearity, accuracy, and precision. Good linear calibrations were obtained for MC-LR (1-200 microg/L; R2=0.9994) in spiked lake and tap water samples (1-50 microg/L; R2=0.9974). Acceptable interday repeatability was achieved for MC-LR in lake water with RSD values (n=9) ranging from 9.9 (10 microg/L) to 5.1% (100 microg/L). Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with spiked MCs and Nod samples; LOD=0.27 microg/L and LOQ=0.90 microg/L for MC-LR in the "normal linear range" and LOD=0.08 microg/L and LOQ=0.25 microg/L in the "low linear range" in both lake and chlorinated tap water. Similar results were obtained for a suite of microcystins and nodularin. This sensitive and rapid method does not require any sample preconcentration, including the elimination of solid-phase extraction (SPE) for the effective screening of hepatotoxins in water below the 1 microg/L WHO provisional guideline limit for MC-LR. Furthermore, SPE techniques are time-consuming, nonreproducible at trace levels, and offer poor recoveries with chlorinated water. The application of this LC-ESI-MS/MS method for routine screening of hepatotoxins in lake and chlorinated tap water (average Cl2=0.23 mg/L) is achieved and this study represents the first direct method for the screening of hepatotoxins in chlorinated tap water.

Enzyme-linked immunosorbent assay detection of microcystins using new monoclonal antibodies

New monoclonal antibodies (mAbs) against the microcystin-leucine-arginine variant (microcystin-LR), a cyclic peptide toxin of the freshwater cyanobacterium Microcystis aeruginosa, were prepared from cloned hybridoma cell lines. Using these mAbs, an enzyme-linked immunosorbent assay (ELISA) experiment was made for the detection of cyanobacterial hepatotoxins, microcystins in water sampled in Soyang Lake, Korea. The performance of the ELISA test with mAbs established in this study was evaluated. The ELISA detection was compared with HPLC detection. Since the detection limit of HPLC is several orders of magnitude higher than with ELISA, attention was also paid to concentration of samples with solid phase extraction cartridges.

Determination of toxic cyclic heptapeptides by liquid chromatography with detection using ultra-violet, protein phosphatase assay and tandem mass spectrometry

Microcystins, toxic cyclic heptapeptides and nodularin-R, a toxic cyclic pentapeptide, were determined using liquid chromatography (LC) with detection using photo-diode array ultra-violet (PDA-UV) and protein phosphatase (PP) assay. Positive fractions were analysed for toxins using collision-induced dissociation (CID) and tandem MS/MS experiments which were carried out simultaneously using electrospray ion-trap instrumentation. Reversed-phase liquid chromatography (LC) using an acetonitrile/water gradient was used for the LC-MS(2) determination of six microcystins standards and nodularin. The molecular related ion species, [M+H](+)([M+2H](2+) in the case of MC-RR), were used as the precursor ions for MS(2) experiments. Optimum calibration and reproducibility data were obtained for MC-LR using LC-MS(2); 0.1-5.0 microg/ml, r2 = 0.992 (n = 3); % RSD < or =7.3 at 0.25 microg MC-LR/ml (n = 3). The detection limit (S/N = 3) was better than 0.1 ng. Water samples for microcystin analysis were first screened using protein phosphatase (PP) assays and positives were concentrated using C-18 solid-phase extraction. The developed method was applied to examine a lake in Ireland contaminated by Microcystis sp. and MC-LR and MC-LA were identified.

Screening for cyanobacterial hepatotoxins, microcystins and nodularin in environmental water samples by reversed-phase liquid chromatography–electrospray ionisation mass spectrometry

Water samples taken from 93 freshwater and brackish water locations in Aland (SW Finland) in 2001 were analysed for biomass-bound microcystins and nodularin, cyanobacterial peptide hepatotoxins, by liquid chromatography-mass spectrometry (LC-MS) in selected ion recording (SIR) and multiple reaction monitoring modes, HPLC-UV, and enzyme-linked immunosorbent assay (ELISA). The extracted toxins were separated on a short C18 column with a gradient of acetonitrile and 0.5% formic acid, and quantified on a Micromass Quattro Micro triple-quadrupole mass spectrometer with an electrospray ion source operated in the positive SIR or scan mode. An injection of 50 pg of microcystin-LR, m/z 995.5, on column gave a signal-to-noise ratio of 17 (peak-to-peak) at the chosen SIR conditions. In-source or MS-MS fragmentation to m/z 135.1, a fragment common to most microcystins and nodularin, was used for confirmatory purposes. Microcystins with a total toxin concentration equal to or higher than 0.2 microg l(-1) were confirmed by all three methods in water samples from 14 locations. The highest toxin concentration in a water sample was 42 microg l(-1). The most common toxins found were microcystins RR, LR and YR with different degrees of demethylation (non-, mono- or didemethylated). Parallel results achieved with ELISA and HPLC-UV were generally in good agreement with the LC-MS SIR results.

Determination of microcystins in lake water using reusable immunoaffinity column

A reusable immunoaffinity column for purification of microcystins in lake water was prepared by coupling anti-microcystin-LR monoclonal antibodies to immunoaffinity support. Thanks to spherical shape of the immunoaffinity support Formyl-Cellulofine used in this study, applied solutions passed the column smoothly even when used repeatedly. Reusability of the column was examined by determining the recoveries of spiked microcystins-RR, -YR and -LR (100ng each) from lake water. After extraction with a Sep-Pak PS2 cartridge containing styrene-divinylbenzene copolymer, the extract was purified with the immunoaffinity column. The immunoaffinity column was regenerated by washing with Tris-HCl buffer containing bovine serum albumin for repeated uses. Recoveries of spiked microcystins from the first use of the column were 87-88%, and 83-88% from the second and third uses, and the recoveries gradually dropped to 63-77% from the 4-5th uses, the results of which indicated that the column could be used repeatedly for three times. The present method was applied to determine microcystins in water collected from three different lakes in Japan in 1999. In a sample from Lake Suwa, microcystins-RR and -LR were determined by high performance liquid chromatography with photodiode array detection and electrospray ionization-liquid chromatography/mass spectrometry.

Detection of microcystins using electrospray ionization high-field asymmetric waveform ion mobility mass spectrometry/mass spectrometry

A combination of electrospray ionization, high-field asymmetric waveform ion mobility spectrometry, and mass spectrometry (ESI-FAIMS/MS) was used to analyze standard solutions of microcystins-LR, -RR, and -YR. The ability of FAIMS to separate ions in the gas phase reduced the amount of background in the mass spectrum without compromising the absolute signal for these microcystins. This reduction in background resulted in a ten-fold improvement in the signal-to-background ratio over conventional ESI-MS. Detection limits, using direct infusion, were determined to be 4, 2, and 1 nM for microcystins-LR, -RR, and -YR, respectively.

On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high-performance liquid chromatography with diode-array detection

The need for a rapid, sensitive and reliable analytical method for cyanobacterial toxins, microcystins, has been emphasized by the awareness of toxic cyanobacteria as a human-health risk through drinking water. A new high-performance liquid chromatographic method with column switching was developed for the determination of microcystin-LR, -RR and -YR from water samples without pre-purification. The filtered water sample was passed through a Zorbax CN precolumn at a flow-rate of 3 ml/min for on-line trace enrichment. After valve switching, concentrated analytes were eluted in back-flush mode and separated on a Luna C18 column with a gradient of acetonitrile -20 mM phosphate buffer (pH 2.5). The method showed excellent precision, accuracy and speed with detection limits of 0.02 microgram/ml from 100 ml of surface water. The total analysis time per sample was about 90 min. This method improves reliability, sensitivity and sample throughput, and shortens the analysis time compared to analysis methods using off-line solid-phase extraction.

A fluorescent microplate assay for microcystin-LR

A fluorescent enzyme inhibition assay for microcystin-LR was developed using a new fluorescent substrate of protein phosphatases 1 (PP1) and 2A (PP2A), 6,8-difluoro-4-methylumbelliferyl phosphate. The PP1 and PP2A inhibition assay for microcystin-LR was performed in a microtiter plate and the fluorescence yielded by the enzymatic hydrolysis of the substrate was quantified in a fluorescence plate reader. The concentration of microcystin-LR causing 50% inhibition of PP1 and PP2A activity (IC50) was 0.01 nM for PP1 and 0.08 nM for PP2A. The measurable range of microcystin-LR was 800 to 0.08 pg/well for both enzymes. The described assay is fast and very sensitive for the detection of microcystin-LR. Furthermore, this assay can be successfully applied to the study of toxins that inhibit PP1 or PP2A.

Biochemical characterization of microcystin toxicity in rainbow trout (Oncorhynchus mykiss)

The kinetics and biochemical effects of microcystins in rainbow trout were studied with freeze-dried toxic cells of Microcystis aeruginosa, strain PCC 7806. Following in vivo exposure the changes in liver histology were observed over a 72 hr period and the absorption of microcystins from the gastrointestinal tract into the blood and liver, as well as the inhibition of hepatic protein phosphatase 1 and 2A activities, were recorded using the protein phosphatase inhibition assay. The interaction between microcystins and trout liver phosphatases was further tested in vitro using the protein phosphatase inhibition assay. The in vivo experiments demonstrated a high organotropy of microcystins for the liver, where rapid and total inhibition of protein phosphatase 1 and 2A activity was observed. Maximal inhibition of phosphatases was observed 3 hr after gavage. At that time-point, approximately 63% of the toxin present in the liver was refractive to detection via the phosphatase inhibition assay and therefore most likely covalently bound to cellular proteins. The inhibition of hepatic protein phosphatases 1 and 2A proved to be transient only, as a progressive increase in phosphatase activity was observed beginning 12 hr after gavage of the fish, reaching approximately 50% of the control activity at 72 hr. In contrast, liver damage continued to progress despite this renewed protein phosphatase activity.

Hepatic necrosis in aged mice by oral administration of microcystin-LR

Aged mice (32 weeks) were orally administered microcystin-LR at 500 micrograms/kg, and injuries of the liver were estimated by microscopy 2 hr after treatment. Sixty-two per cent of aged mice proved to be sensitive to microcystin-LR, whereas such changes in the liver were not found in young mice (5 weeks). Uptake of the toxin into the liver was confirmed by high-performance liquid chromatography and frit-fast atom bombardment liquid chromatograph/mass spectrometry after clean-up with an immunoaffinity column. To verify the difference in sensitivity to microcystin-LR between aged and young mice, non-treated mice were examined, and among them aged mice were confirmed to have a rough surface of the stomach and small intestinal mucosa. These results suggested that the hepatotoxicity by oral administration of microcystin-LR is deeply related to aging, and particularly to conditions in the small intestine such as the permeability of capillaries in the villi.

Microcystin levels during 1992-95 for Lakes Sagami and Tsukui-Japan

Toxic cyanobacterial blooms have been frequently observed in Lakes Sagami and Tsukui, Kanagawa Prefecture, Japan, which are used as drinking and recreational water sources. As the first step toward the control and removal of cyanobacterial toxins, the present study evaluated the microcystin level in these lakes. Our established method using HPLC and LC/MS to pursue trace amounts of microcystins was applied to the determination of microcystins within cyanobacteria cells and in water. We could determine precisely the intracellular and extracellular microcystin level in the water environment during 1992-95. Microcystins RR, LR, and YR were detected at 0.02-2.64 micrograms/L in cell-free water and at 0.02-378 micrograms/L in the cells. Although there were many cases in which microcystin concentrations in the cells exceeded the proposed guideline level (1 microgram/L), there was only one example of this happening in cell-free water samples. Because the present monitoring indicated that the amount of microcystins detected in water was much less than that estimated in cells, the release of microcystins from the cells and their stability in lake water were examined in the dark. The resulting toxins persisted at the same concentration level for 14 days and the microcystin concentrations steadily declined, showing that biodegradation using aquatic natural bacterial flora is an effective detoxification process under natural conditions.

Mass spectrometric screening method for microcystins in cyanobacteria

A screening method for microcystins in cyanobacteria, which consists of the formation of 3-methoxy-2-methyl-4-phenylbutyric acid as an oxidation product of microcystins by ozonolysis, and detection of 3-methoxy-2-methyl-4-phenylbutyric acid by thermospray-liquid chromatography/mass spectrometry or electron ionization-gas chromatography/mass spectrometry using selected ion monitoring, was developed. The ozonolysis made it possible to significantly reduce the formation times of 3-methoxy-2-methyl-4-phenylbutyric acid because the previously required extraction, clean-up and other procedures could be entirely eliminated. The resulting intact 2-methyl-4-phenylbutyric acid was directly analyzed by thermospray-liquid or electron ionization-gas chromatography/mass spectrometry, and the procedures from ozonolysis to analysis of microcystins at the pmole levels were performed within only 30 min. The calibration curves obtained by thermospray-liquid or electron ionization-gas chromatography/mass spectrometry analysis showed a linear relationship from 14 to 830 pmole and from 2.5 to 100 pmole of microcystin-LR, respectively. The method was applied to the detection and determination of the total amount of microcystins in bloom and cultured samples, showing that it provided a means of not only screening for microcystins but of their accurate quantitation.

Stability of microcystins from cyanobacteria--II. Effect of UV light on decomposition and isomerization

Microcystins are very potent hepatotoxins and strong liver tumor promoters produced by cyanobacteria, and their occurrence has been reported all over the world. They could threaten human health when toxic Microcystis occurs in water supply reservoirs. In this study, we examined the stability of microcystins during photolysis with UV light. The toxins were easily decomposed by UV light at wavelengths around the absorption maxima of the toxins and the decomposition depended on the intensity of the light. The half-life of microcystin LR by 147 microW/cm2 UV irradiation was 10 min, and the toxin was completely decomposed by 2550 microW/cm2 UV after 10 min. When the toxins were irradiated with weaker UV light, isomerization was also observed by a different mechanism from that during photolysis by sunlight and pigment, and several products including three geometrical isomers of the conjugated diene of Adda were detected. Microcystin RR showed almost the same behavior as that of microcystin LR under the same conditions. Since no noxious products were formed in the present study, a water treatment including UV irradiation is very possible for removing microcystins from raw water.

Mass spectral analyses of microcystins from toxic cyanobacteria using on-line chromatographic and electrophoretic separations

The application of capillary electrophoresis and of reversed-phase liquid chromatography coupled to electrospray mass spectrometry is presented for the analysis of microcystins isolated from toxic strains of Microcystis aeruginosa. The separation performance of these two techniques is compared in terms of both sensitivity and of resolution of closely related microcystins. Quantitation of microcystin-LR present at low micrograms/ml concentrations in cell extracts is demonstrated using both techniques. A marked advantage of capillary electrophoresis over liquid chromatography was its ability to resolve different desmethyl microcystin-LR analogues. Identification of these positional isomers was facilitated using capillary electrophoresis combined with tandem mass spectrometry (MS-MS). Rationalization of fragment ions observed in MS-MS spectra of microcystins was made possible through comparison with 15N labelled microcystins obtained from stable isotope feeding experiments. The potential of tandem mass spectrometry in providing selective detection of microcystins in cell extracts, and in structural characterization of novel microcystins, was also investigated.

Reliable and sensitive method for determination of microcystins in complicated matrices by frit-fast atom bombardment liquid chromatography/mass spectrometry

A reliable and sensitive method for determination of hepatotoxic microcystins in complicated matrices by frit-fast atom bombardment liquid chromatography/mass spectrometry (Frit-FAB LC/MS) is described. Immonium ions of constituent amino acids, which were obtained together with molecular ion species by FAB mass spectral analysis of standard microcystins RR, YR, LR, and [D-Asp3] and [Dha7]microcystins LR using flow injection system composed of Frit-FAB probe, showed potential for reliable identification of microcystins by Frit-FAB LC/MS. Frit-FAB LC/MS using a microbore column provided not only the baseline separation of standard microcystins RR, YR, and LR but 200-fold higher sensitivity than that using conventional column. Furthermore, when a selected ion monitoring (SIM) technique was used, the detection limits of microcystins RR, YR, and LR were 300, 350, and 400 pg, respectively, at a signal-to-noise ratio of 5:1, and calibration curves of each microcystin showed a linear relationship from 2 ng to 50 ng. Finally, identification and quantitative analyses of microcystins in water samples were carried out.

A clean-up method for analysis of trace amounts of microcystins in lake water

A clean-up method using high performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) was developed to pursue trace amounts of microcystins in lake water. The method consisted of the combined usage of octadecyl silanized (ODS) silica gel and silica gel cartridges. In the first clean-up process, the retention behavior of microcystin RR on ODS silica gel cartridge was carefully observed together with microcystin LR, and 10% water-methanol was chosen as the best solvent system to elute microcystins from the ODS silica gel cartridge. Because many impurities still remained in the desired fraction from the raw water even after the clean-up with ODS silica gel, an additional clean-up process was developed using various cartridges. As a result of extensive experiments, the second clean-up process using silica gel cartridge was established, and the impurities were effectively eliminated. The present method including a tandem cartridge system allowed a precise analysis of microcystins in water samples from three different lakes at a 0.02 ppb level.

Protein phosphatase activity in cyanobacteria: consequences for microcystin toxicity analysis

Hepatotoxic microcystin levels in cyanobacteria (blue-green algae) were assessed by an assay based on inhibition of protein phosphatases type 1 (PP1) and type 2A (PP2A) in crude chicken forebrain extracts using 32P-labelled glycogen phosphorylase as substrate. While cyanobacteria are reported to be devoid of phosphorylase phosphatase activity, two samples obtained from cyanobacterial scums, containing predominantly Anabaena circinalis, were found to contain high levels of a phosphorylase phosphatase activity which completely masked the presence of microcystin. Furthermore, samples containing predominantly Microcystis aeruginosa but increasing Anabaena circinalis contained sufficient phosphorylase phosphatase activity to cause a fourfold underestimation of microcystin levels. Thus, protocols for microcystin toxicity analysis should take into account the possible presence of endogenous phosphatase activity, thereby preventing underestimation of toxin levels.