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PubMed2003

Development of an ultrarapid one-step fluorescence immunochromatographic assay system for the quantification of microcystins.

Microcystins are a family of potent toxic oligopeptides produced by freshwater cyanobacteria genera and have been a great threat to the welfare of humans and animals. There has been a great demand for developing a fast and convenient analytical method to detect microcystins. Recently, direct competition ELISA using monoclonal or polyclonal antibody has become the prevailing method for detecting microcystins. In this study, we report rapid quantification methods of microcystins using fluorescence for a detection signal and a lateral-flow-type immunochromatography as a separation system. The assay systems consist of a test strip housed in a disposable cartridge and a portable laser-fluorescence scanner. The components of a test strip are as follows: a nitrocellulose membrane, a sample pad, an absorption pad, and a backing card. A fluorescence scanner was designed to fit the cartridge and to quantify the distribution of the fluorescence intensity along the strip. When the calibration curve for an antibody-immobilized system was determined, a good linearity was displayed in the range from 125 to 2000 pg/mL of microcystin-LR. The linear-regression coefficient (R) was 0.938 between relative fluorescence intensity and the microcystin concentration. The limit of detection was determined to be 95.38 pg/mL. We then designed another biosensor system by changing an experimental format from the competition type to the inhibition type. When compared to the antibody-immobilized system, the antigen-immobilized assay detected a lower level of microcystin but did not discern microcystin-LR above 1000 pg/mL. The detection of limit for the antigen-immobilized system was 47.23 pg/mL. The linear regression coefficient (R) in the antigen-immobilized system equaled to 0.927. The reproducibility in the antigen-immobilized system was good through the entire range. The reproducibility in the antibody-immobilized system was relatively poor when compared to a MC-immobilized system. However, it still registered in the acceptable range of 7.32-9.91% except for the extreme ends of the MC concentration. Finally, surface water was tested to check for potential matrix interference. The calibration curve displayed a similar pattern as did those for other matrixes, including PBS and tap water, although its sensitivity was a little less due to the interference with certain components in the surface water. Overall, either of the biosensor systems can be used as a useful on-site detection tool for checking drinking water or surface water for microcystins. The laser-fluorescence scanner we developed is relatively small, transportable, and easy to use. Thus, the samples can be analyzed for microcystins at the test site using a real-time base within 15 min without having to bring the samples back to the laboratory.

Automation↗

PubMed2005

Bacterial degradation of microcystins and nodularin.

Microcystins and nodularins produced by cyanobacteria are potent hepatotoxins and tumor promoters. They are, respectively, cyclic heptapeptides and cyclic pentapeptides containing a characteristic beta-amino acid residue, (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4(E ),6(E)-dienoic acid (Adda). Strain B-9 isolated from Lake Tsukui, Japan, degrades microcystin-LR, which is the most toxic among the microcystins, to nontoxic Adda as an end product. In the present study, we characterized the bacterial degradation process of the cyclic peptide hepatotoxins by liquid chromatography/ion trap tandem mass spectrometry. The use of protease inhibitors with a B-9 cell extract indicated that the degradation process of microcystin-LR consists of sequential enzymatic hydrolyses of Arg-Adda, Ala-Leu, and then Adda-Glu peptide bonds into two known nontoxic intermediate degradation products and then Adda, respectively. Subsequently, additional microcystins and nodularin were compared with microcystin-LR on substrate specificity. The cyclic peptides containing the Arg-Adda peptide bond were almost completely degraded to Adda as well as microcystin-LR, whereas microcystin-LF containing the Phe-Adda peptide bond instead of Arg-Adda peptide bond and 6(Z)-Adda-microcystin-LR and -RR which are geometrical isomers of the Adda residue were barely degraded. These results indicated that the degrading enzymes selectively hydrolyzed the Arg-Adda peptide bond as the initial ring opening of the cyclic peptide hepatotoxins, microcystins and nodularin.

Bacterial Toxins↗

PubMed2000

Detection and quantification of microcystins (cyanobacterial hepatotoxins) with recombinant antibody fragments isolated from a naïve human phage display library.

Single-chain antibody fragments against the cyanobacterial hepatotoxin microcystin-LR were isolated from a naive human phage display library and expressed in Escherichia coli. In competition enzyme-linked immunosorbent assay (ELISA), the most sensitive antibody clone selected from the library detected free microcystin-LR with an IC(50) value of 4 microM. It was found to cross react with three other microcystin variants - microcystin-RR, microcystin-LW and microcystin-LF - and detected microcystins in extracts of the cyanobacterium Microcystis aeruginosa, found to contain the toxins by high-performance liquid chromatography (HPLC). The quantification of microcystins in these extracts by ELISA and HPLC showed good correlation. Although the antibody isolated in this study was considerably less sensitive than the polyclonal and monoclonal antibodies already available for microcystin detection, phage display technology represents a cheaper, more rapid alternative for the production of anti-microcystin antibodies than the methods currently in use.

Antibody Specificity↗

PubMed2005

The microcystin composition of the cyanobacterium Planktothrix agardhii changes toward a more toxic variant with increasing light intensity.

The cyanobacterium Planktothrix agardhii, which is dominant in many shallow eutrophic lakes, can produce hepatotoxic microcystins. Currently, more than 70 different microcystin variants have been described, which differ in toxicity. In this study, the effect of photon irradiance on the production of different microcystin variants by P. agardhii was investigated using light-limited turbidostats. Both the amount of the mRNA transcript of the mcyA gene and the total microcystin production rate increased with photon irradiance up to 60 micromol m(-2) s(-1), but they started to decrease with irradiance greater than 100 micromol m(-2) s(-1). The cellular content of total microcystin remained constant, independent of the irradiance. However, of the two main microcystin variants detected in P. agardhii, the microcystin-DeRR content decreased twofold with increased photon irradiance, whereas the microcystin-DeLR content increased threefold. Since microcystin-DeLR is considerably more toxic than microcystin-DeRR, this implies that P. agardhii becomes more toxic at high light intensities.

Bacterial Proteins↗

PubMed1996

Molecular mechanisms underlying he interaction of motuporin and microcystins with type-1 and type-2A protein phosphatases.

Heptapeptide microcystin and pentapeptide motuporin (nodularin-V) are equipotent inhibitors of type-1 and type-2A protein phosphatase catalytic subunits (PP-1c and PP-2Ac). Herein we describe elucidation of the molecular mechanisms involved in the interaction of these structurally similar hepatotoxins with PP-1c/PP-2Ac and identification of an important functional difference between their mode of interaction with these enzymes. Microcystin-LR, microcystin-LA, and microcystin-LL were found to interact with PP-2Ac and PP-1c by a two-step mechanism involving rapid binding and inactivation of the protein phosphatase (PPase) catalytic subunit, followed by a slower covalent interaction (within hours). Covalent adducts comprising PPase-toxin complexes were separated from free PPase by C-18 reverse-phase liquid chromatography, thus allowing the time course of covalent adduct formation to be quantitated. In contrast to microcystins, motuporin (nodularin-V) and nodularin-R were unable to form covalent complexes with either PP-1c or PP-2Ac even after 96 h incubation. Specific reduction of microcystin-LA to dihydromicrocystin-LA abolished the ability of the toxin to form a covalent adduct with PP-2Ac. Specific methyl esterification of the single Glu residue in microcystin-LR rendered this toxin inactive as a PPase inhibitor and abolished subsequent formation of a covalent adduct. Our data indicate that inactivation of PP-2Ac/PP-1c by microcystins precedes covalent modification of the PPases via a Michael addition reaction between a nucleophilic phosphatase residue and Mdha in the heptapeptide toxin. In contrast, following rapid inactivation of PP-2Ac/PP-1c by motuporin, the equivalent N-methyldehydrobutyrine residue in this toxin is unreactive and does not form a covalent bond with the PPases. These results are consistent with structural data for (i) the NMR solution structures of microcystin-LR and motuporin, which indicate a striking difference in the relative positions of their corresponding dehydroamino acids in the toxin peptide backbone, and (ii) X-ray crystallographic data on an inactive complex between PP-1c and microcystin-LR, which show a covalent bond between Cys-273 and the bound toxin.

Enzyme Inhibitors↗

PubMed2001

Occurrence of microcystins in raw water sources and treated drinking water of Finnish waterworks.

Problems caused by cyanobacteria are common around the world and also in raw water sources of drinking water treatment plants. Strains belonging to genera Microcystis, Anabaena and Planktothrix produce potent hepatotoxins, the microcystins. Laboratory and pilot scale studies have shown that microcystins dissolved in water may pass the conventional surface water treatment processes. In 1998 the World Health Organization proposed a guide value of 1 microgram/L for microcystin-LR (MC-LR) in drinking water. The purpose of this research was to study the occurrence of microcystins in raw water sources of surface waterworks and in bank filtration plants and to evaluate the removal of microcystins in operating waterworks. Four bank filtration plants and nine surface waterworks using different processes for water treatment were monitored. Phytoplankton was identified and quantified, and microcystins analysed with sensitive immunoassay. Microcystin occurrence in selected water samples was verified with HPLC and a protein phosphatase inhibition method. Microcystins were detected sporadically in raw water sources of most of the waterworks. In two raw water supplies toxins were detected for several months. The highest microcystin concentrations in incoming raw water were approximately 10 micrograms/L MC-LR equivalents. In treated drinking water microcystins were detected occasionally but the concentrations were always below the guide value proposed by WHO.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Comparison of liquid chromatography/mass spectrometry, ELISA, and phosphatase assay for the determination of microcystins in blue-green algae products.

More than 100 samples of blue-green algae products (consisting of Aphanizomenon, Spirulina, and unidentified blue-green algae) in the form of pills, capsules, and powders were collected from retail outlets from across Canada. The samples were extracted with 75% methanol in water and centrifuged to remove solids. Aliquots of the extracts along with spiked blank sample extracts were sent to each participating laboratory and independently analyzed for microcystins by enzyme-linked immunosorbent assay (ELISA), protein phosphatase inhibition assay, and by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after sample cleanup using C18 solid-phase extraction. The results obtained by ELISA and LC-MS/MS agreed very well over a concentration range of about 0.5-35 microg/g. The colorimetric phosphatase results generally agreed with the other 2 methods. While the 2 biochemical assays measured total microcystin content compared with a standard of microcystin LR, the LC-MS/MS method measured specific microcystins (LA, LR, RR, YR) using external standards of these for identification and quantitation. Microcystin LR was found in all positive samples by LC-MS/MS. Microcystin LA was the only other microcystin found in the samples analyzed. These 2 microcystins represent essentially all the microcystins that were present in the extracts. Otherwise, the LC-MS/MS results would have been significantly lower than the results of the biochemical assays had other unknown microcystins been present.

Chromatography, Liquid↗

PubMed1997

Seasonal variations in microcystin contents of Danish cyanobacteria.

One hundred ninety-eight of 296 phytoplankton net samples, collected from Danish fresh waters during 1993-1995, contained microcystins when analyzed by high-performance liquid chromatography (HPLC), and the seasonal variations in microcystin contents were examined. Three genera, Anabaena, Microcystis, and Planktothrix, with microcystin-production potential were found. The highest percentage of the samples dominated by Anabaena and Microcystis was found in June-July and July-November, respectively, and those by Planktothrix in May and October-November. The highest microcystin contents were found in samples collected in July and September. When pooling all samples by month of collection, no major differences in mean toxin contents were seen in samples collected from May through November, with the exception of slightly higher microcystin contents in September and October. The frequency of samples (all samples grouped by month of collection) with detected microcystins ranged from 62% in July (n = 116) to 86% in May (n = 7). Variations in toxin profiles were found between 5 lakes sampled several times during 1993-1995, and in addition, quantitative and qualitative seasonal changes in microcystin content accompanied species composition changes in 3 of these lakes. Consistent blooms dominated by single species were characterized by more or less constant toxin profiles but variable toxin concentrations. Analysis of 6 samples from Lake Bryrup Langsø 1995 by enzyme linked immunoabsorbent assay and HPLC revealed 1-70 and 0-737 micrograms microcystins/g dry wt, respectively. The discrepancy between the two detection methods may be attributed to the types of microcystin variants present, emphasizing the possible influence of seasonal variations in toxin profiles on the quantification of microcystins.

Carcinogens↗

PubMed1996

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.

Biodegradation, Environmental↗

PubMed1992

Release of heptapeptide toxin (microcystin) during the decomposition process of Microcystis aeruginosa.

The decomposition process of toxic blue-green alga (cyanobacteria), Microcystis aeruginosa, under dark and aerobic condition was investigated in relation to the change of the amounts of heptapeptide toxins (microcystins YR and LR) by two experiments: one with Microcystis cells and the other with two purified microcystins. In the experiment with Microcystis cells, an increase of heterotrophic bacteria observed from the beginning of the experiment, was followed by decomposition of the algal cells and the subsequent release of microcystins into the filtrate fraction. The amounts of the toxins initially present in the cells were quantitatively detected in the filtrate fraction on the 35th day. The decomposition of microcystin YR began on the 42nd day. The decomposition rate of the two toxins was different. The decomposition rate of purified microcystins YR and LR, compared in distilled water and culture medium, respectively, indicated clearly that microcystin YR was more labile to decomposition than microcystin LR in the culture medium. At the end of the experiment (45th day) microcystin YR decreased to 58.6%, while 86.2% of microcystin LR remained.

Bacterial Toxins↗

PubMed2002

Removal of microcystins by slow sand filtration.

To assess the elimination potential of slow sand filters for cyanobacterial hepatotoxins (microcystins), two full-scale experiments were conducted using the German Federal Environment Agency's experimental field in Berlin, Germany. One experiment was carried out with dissolved microcystins extracted from a cyanobacterial bloom on one of Berlin's lakes, dosed as short-term, single-pulse application. The other experiment simulated natural conditions more closely, with a longer-term exposure of the filter to living cyanobacterial cells (collected from the same lake) so that most toxins were initially contained inside the cells. The microcystins were detected by ELISA and HPLC/photodiode array detector and subsequently identified by MALDI-TOF MS. The experiment with dissolved microcystins yielded very high elimination rates (>95%) inside the filter bed attributed to biodegradation, whereas retardation by adsorption was low. The obtained half-lives for the microcystins detected by ELISA were about 1 h. The second experiment, which was with mostly cell-bound microcystins, showed similar results during the first days after application of cyanobacteria (elimination >85%). As the population declined in late autumn, the proportion of extracellular to cell-bound microcystins increased. At the same time the elimination rates declined to values <60%. This decline is most likely attributable to retarded biodegradation at temperatures of <4 degrees C. Altogether the results of the experiments show that under moderate temperatures, with an intact schmutzdecke (biofilm) with previous contact with microcystins, slow sand filtration is an effective treatment for eliminating microcystins from drinking water.

Biofilms↗

PubMed2006

Changes in concentrations of microcystins in rainbow trout, freshwater mussels, and cyanobacteria in Lakes Rotoiti and Rotoehu.

Microcystin concentrations in cyanobacteria and their accumulation in rainbow trout (Oncorhynchus mykiss) and freshwater mussels (Hyridella menziesi) in Lakes Rotoiti and Rotoehu (New Zealand) were investigated. Hatchery rainbow trout were added to an enclosure in Lake Rotoiti where concentrations of microcystins in the phytoplankton and cyanobacterial cell concentrations could be closely monitored. Rainbow trout that were free to roam in the entire area of each lake were also included in the study. Freshwater mussels were suspended subsurface in cages in the enclosure. Phytoplankton samples, rainbow trout liver and muscle tissue, and the tissues of mussels were analyzed for microcystins using the ADDA-ELISA method, and selected samples were analyzed using LC-MS. A maximum concentration of microcystins in the phytoplankton samples of 760 microg L(-1) was recorded in Te Weta Bay, Lake Rotoiti, in March 2004. ELISA results confirmed microcystin immunoreactivity in rainbow trout liver and muscle tissues and in freshwater mussels. The microcystin congeners LR, YR, RR, AR, FR, LA, and WR were detected by LC-MS in caged freshwater mussels in Lake Rotoiti but were not detected in either muscle or liver tissue of rainbow trout. The daily tolerable intake limit of microcystins for human consumption recommended by the World Health Organisation is 0.04 microg kg(-1) day(-1). Modeling was carried out for the human intake of microcystin compounds from rainbow trout muscle tissue, and the potential health risks were estimated, assuming the ADDA-ELISA was determining compounds of toxicity equivalent to microcystin-LR.

Animals↗

PubMed2004

First report of a microcystin-containing bloom of the cyanobacteria Microcystis spp. in Lake Oubeira, eastern Algeria.

Lake Oubeira has been used as the main source of drinking water for many communities in the East of Algeria. In this lake, nutrient loading coupled with year-round warm weather favors the growth of cyanobacteria, several of which can produce cyanotoxins, especially the potent liver toxins called microcystins (MCYSTs). The present study evaluated microcystin levels and characterized the different microcystin variants present in the raw water during a 17-month period (April 2000-September 2001), as measured by protein phosphatase inhibition assays and by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, respectively. The results showed that microcystin concentrations in the lake water varied between 3 and 29,163 microg microcystin-LR equivalent per liter. The microscopic examination of the phytoplankton samples showed the dominance of the Microcystis genus in the cyanobacterial bloom. The highest MCYST concentration was observed in August 2001, at 29,163 microg/l. Therefore, the highest total MCYST content per phytoplankton biomass was found in August 2001, with 4,590 microg MCYST-LR equivalents/g dried bloom material. Analysis of the field bloom extract by MALDI-TOF mass spectrometry demonstrated the presence of four variants of microcystins: microcystin-LR (MCYST-LR), microcystin-YR (MCYST-YR), microcystin-RR (MCYST-RR), and a demethylated variant of MCYST-LR (D-MCYST-LR).

Algeria↗

PubMed1994

Use of a colorimetric protein phosphatase inhibition assay and enzyme linked immunosorbent assay for the study of microcystins and nodularins.

Microcystins and nodularins are cyclic peptide hepatotoxins and tumor promoters produced by several genera of cyanobacteria. Using a rabbit anti-microcystin-LR polyclonal antibody preparation, the cross-reactivity with 18 microcystin and nodularin variants was tested. A hydrophobic amino acid, 3-amino-9-methoxy-10-phenyl-2,6,8-trimethyl-deca-4(E),6(E)-dienoic acid (Adda), which has the (E) form at the C-6 double bond in both microcystin and nodularin, was found essential for these toxins to express antibody specificity. Modification of -COOH in glutamic acid of microcystin and nodularin did not alter their antigenicity. Antibody cross-reactivity of these toxins was compared with their ability to inhibit protein phosphatase type 1 (PP1). Detection of PP1 inhibition was done by measuring the inhibition effect of the toxins on p-nitrophenol phosphate activity toward PP1. PP1 was obtained as recombinant PP1 expressed in E. coli. The inhibition effect of five microcystins and two nodularins on recombinant PP1 activity toward p-nitrophenol phospate was measured in a microwell plate reader. The concentration of microcystin-LR causing 50% inhibition of recombinant PP1 activity (IC50) was about 0.3 nM, while that of two modified microcystins had a significantly higher IC50. Microcystin-LR and nodularin with the (z) form of Adda at the C-6 double bond or having the monoester of glutamic acid did not inhibit PP1. These three toxins were also nontoxic in the mouse bioassay. These results show the importance of Adda and glutamic acid in toxicity of these cyclic peptides and that PP1 inhibition is related to the toxins' mechanism of action.

Amino Acids↗

PubMed2005

Guidance values for microcystins in water and cyanobacterial supplement products (blue-green algal supplements): a reasonable or misguided approach?

This article reviews current scientific knowledge on the toxicity and carcinogenicity of microcystins and compares this to the guidance values proposed for microcystins in water by the World Health Organization, and for blue-green algal food supplements by the Oregon State Department of Health. The basis of the risk assessment underlying these guidance values is viewed as being critical due to overt deficiencies in the data used for its generation: (i) use of one microcystin congener only (microcystin-LR), while the other presently known nearly 80 congeners are largely disregarded, (ii) new knowledge regarding potential neuro and renal toxicity of microcystins in humans and (iii) the inadequacies of assessing realistic microcystin exposures in humans and especially in children via blue-green algal food supplements. In reiterating the state-of-the-art toxicology database on microcystins and in the light of new data on the high degree of toxin contamination of algal food supplements, this review clearly demonstrates the need for improved kinetic data of microcystins in humans and for discussion concerning uncertainty factors, which may result in a lowering of the present guidance values and an increased routine control of water bodies and food supplements for toxin contamination. Similar to the approach taken previously by authorities for dioxin or PCB risk assessment, the use of a toxin equivalent approach to the risk assessment of microcystins is proposed.

Animals↗

PubMed2004

The uptake kinetics and immunotoxic effects of microcystin-LR in human and chicken peripheral blood lymphocytes in vitro.

Microcystin-LR is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. We investigated the influence of this toxin on human and chicken immune system modulation in vitro. Peripheral blood lymphocytes were treated with microcystin-LR at environmentally relevant doses of 1, 10 and 25 microg/ml for 12, 24, 48, 72 h (for proliferation assay cells were treated for 72 h). T-cell and B-cell proliferation as well as apoptosis and necrosis were determined in human and chicken samples. IL-2 and IL-6 production by human lymphocytes also was measured. In addition, uptake kinetics of microcystin-LR into human and chicken peripheral blood lymphocytes were calculated by Liquid Chromatography (LS) /Mass Spectrometry (MS) analysis. At the highest dose microcystin-LR decreased T-cell proliferation and all doses of microcystin-LR inhibited B-cell proliferation. The frequency of apoptotic and necrotic cells increased in a dose and time-dependent manner. Human lymphocytes responded to stimulation with microcystin-LR by increased production of IL-6 and decreased production of IL-2. Human lymphocytes were able to uptake from 0.014 to 1.663 microg/ml and chicken lymphocytes from 0.035 to 1.733 microg/ml of the microcystin-LR added to the cultures, depending on the treatment time and dose. In conclusion, microcystin-LR acted as an immunomodulator in cytokine production and down-regulated lymphocyte functions by induction of apoptosis and necrosis. However, further studies dealing with the influence of microcystin-LR on expression cytokine genes and transcription factors are necessary to confirm these hypotheses.

Animals↗

PubMed2005

An advanced technique for immuno-labelling of microcystins in cryosectioned cells of Microcystis aeruginosa PCC 7806 (cyanobacteria): implementations of an experiment with varying light scenarios and culture densities.

The intracellular localisation of cyanobacterial toxins might well indicate production sites and possible shifts to destination points, thus giving information on possible functions of these toxins within algal cells or at the ecological level beyond. By preparing cells of Microcystis aeruginosa PCC 7806 by cryofixation/cryosectioning and using purified high quality antibodies for immunogold-localisation, excellent ultrastructural integrity and labelling of microcystins was shown. Compared to conventional techniques, including organic solvents, possible dislocation/extraction was significantly minimised, hence, the labelling density was enhanced and the labelling pattern changed. The microcystins were mainly localised within the inner nucleoplasmic area and accumulations of epitopes could be detected around/within intracellular inclusions, such as polyphosphate bodies and carboxysomes. Photosynthetic active radiation (PAR) had a significant effect on microcystin biosynthesis, and the medium light intensity of 25 microE m(-2) s(-1) induced the highest intracellular microcystin contents (up to 160 epitopes per cell and 26 epitopes per microm2). The restriction of the full light spectrum to blue (400-500 nm) or red (>610 nm) wavelengths did not result in any significant effect on microcystin production. However, the subcultures harvested at higher optical densities (>0.5) revealed significantly higher microcystin labelling compared to the less dense cell cultures (OD < 0.5). Altogether, the possibility was discussed whether microcystin might function as an inhibitor of RUBISCO under conditions of C-limitations. The effects of light intensity and cell suspension density on intracellular microcystin shown by immuno-detection matched the pattern of microcystin concentrations determined in parallel by HPLC and ELISA.

Biological Transport↗

PubMed2006

Differences in the chlorine reactivity of four microcystin analogues.

The presence of microcystin toxins in drinking water is highly undesirable as they have the potential to adversely affect human health. Consequently, effective removal of these toxins from water is a major goal for water authorities. In this study, four microcystin analogues were chlorinated in two treated waters, and two of the analogues were chlorinated in deionised water. The oxidation of the microcystins was related to the chlorine exposure (CT) of the sample waters with the ease of oxidation following the trend: microcystin-YR > microcystin-RR > microcystin-LR > or = microcystin-LA. This trend was in agreement with published data on model compounds and free amino acids. Values of CT of up to 25 mg min L(-1) were required for oxidation of all microcystin analogues to below the World Health Organization guideline value of 1.0 microg L(-1). Results from this study indicate that for some water resources it is important to determine the speciation of the microcystin analogues to optimise chlorination practices.

Chlorine↗