The peptide toxin of the cyanobacterium Microcystis aeruginosa PCC 7941. Isolation and analysis by nuclear magnetic resonance and fast atom bombardment mass spectroscopy

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.

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.

Toxin extraction from an Anabaenopsis milleri--dominated bloom

This paper reports the presence of microcystin type toxins in extracts of a natural bloom of cyanobacteria composed predominantly of Anabaenopsis milleri Woronichin. The toxins have been extracted, purified and compared to microcystin-LR. The LD50 of A. milleri bloom material was 600-1500 mg lyophilized cells/kg body weight. Symptoms and pathological signs of poisoning in mice were characteristic of cyanobacterial hepatotoxins, with enlarged darkened livers with weights of 8-10% of the total body weight. Thin-layer chromatography of the extract resulted in one toxic band, which was separated from pigments and 280-nm absorbing compounds. The toxic fraction was further separated using reversed phase high performance liquid chromatography and one toxic band was recovered. This fraction yielded a single, toxic peak with a retention time of 11.3 min after high performance liquid chromatography. The absorption spectrum of the purified toxin had a maximum at 238-240 nm and was characteristic of cyanobacterial hepatotoxic peptides. Comparison of the chromatographic behaviour of the purified toxin with microcystin-LR on reversed phase and on internal surface reversed phase, high performance liquid chromatography indicated that an A. milleri bloom material toxin was a microcystin type toxin and it is highly likely that the purified toxin is microcystin-LR.

Identification and characterization of microcystin-LY from Microcystis aeruginosa (strain 298)

Two toxins, a main component A and a minor component B, were isolated from the freshwater cyanobacterium Microcystis aeruginosa (strain 298) and characterized in their chemical structure by amino-acid analysis, configurational analysis, by FAB-MS and 1H-NMR spectroscopy. The acid hydrolysate yielded for toxin A as constituent amino acids D-Ala, L-Leu, D-Glu, erythro-D-beta-Me-Asp and L-Arg, and for toxin B the amino acids D-Ala, L-Leu, D-Glu, erythro-D-beta-Me-Asp and L-Tyr. 1D and 2D 1H-NMR spectroscopy of the toxins A and B in DMSO-d6 allowed to characterize them as cyclic heptapeptides containing both the unusual beta-amino acid Adda (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid) and N-methyldehydroalanine (Mdha) as additional constituent residues. Toxin A was found to correspond to the known and structurally well characterized microcystin-LR and toxin B to microsystin-LY. The presence of this variant has already been proposed, but its primary structure could be confirmed in this study.

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

In order to separate and identify microcystins, a new analytical method was developed using a frit probe as an interface for fast atom bombardment mass spectral analysis of high performance liquid chromatographic (HPLC) effluents. Two types of HPLC conditions were designed for separation of standard microcystins RR, YR and LR. The HPLC conditions, for example, methanol:0.01% trifluoroacetic acid = 61:39 (containing 0.8% glycerol) as a mobile phase and 0.5 ml/min as a flow rate, provided a base line separation of standard microcystins RR, YR and LR. The HPLC conditions were also effective for separation of the non-toxic geometrical isomers of microcystins RR and LR. The total ion chromatogram of a mixture of standard microcystins showed excellent correlation with the HPLC separation using a u.v. detector. The method was subsequently applied to analysis of microcystins contained in both a culture strain and a field sample, and the procedure from toxin extraction to identification of microcystins was performed within 1 day. The mass chromatogram monitored at m/z 135 that is always observed with abundance in the FAB mass spectra of the purified microcystins, differentiated between microcystins and other types of compounds. This technique allowed the rapid identification of unknown microcystins without standard samples. Additionally, compounds other than microcystins were also found, which would not be seen by u.v. detection at 238 nm.

Algae intoxication in livestock and waterfowl

Blue-green algae toxins include (1) hepatotoxic peptides that are known to be toxic to cattle, dogs, swine, waterfowl, and sometimes other species; (2) a nicotinic agonist neurotoxin that appears to be toxic to a wide range of animal species; (3) a peripheral-acting cholinesterase inhibitor that is very toxic to swine, birds, and dogs; (4) toxins that impair nervous transmission by blocking sodium channels in nerve cells; and (5) lipopolysaccharide endotoxins. This article provides current information on the mechanisms of action of the primary toxins recognized to date as well as on procedures important in the diagnosis and management of some of the more common cyanobacterial toxicoses in livestock and waterfowl.

Nontoxic and toxic oligopeptides with D-amino acids and unusual residues in Microcystis aeruginosa PCC 7806

Toxic and nontoxic peptides were isolated from the cyanobacterium Microcystis aeruginosa PCC 7806 by a procedure including extraction of cells with water-saturated 1-butanol, chromatography of the extract on silica gel plates and high performance liquid chromatography (HPLC) on Partisil-5. The toxin was shown to be only a minor constituent, being negatively charged and thus separable by electrophoresis, within the HPLC-purified fraction. It contained erythro-beta-methyl-D-Asp, D-Glu, D-Ala, L-Leu, and L-Arg known to be part of the Microcystis peptide-toxin with Mr 994. The major part of the HPLC-purified fraction was assigned, however, to a nontoxic peptide with a Mr of 956. Partial hydrolysis studies of the nontoxic peptide(s) revealed amino acid sequences composed of D-Glu, N-methyl-Phe, and 3,4-dehydro-Pro, aside from the common L-amino acids. Cyclic linkage in the nontoxic peptide(s) appears likely.