First report of microcystins from a Brazilian isolate of the cyanobacterium

This is the first report on microcystins, cyclic heptapeptide hepatotoxins, from Brazilian water supplies. A colony isolate (NPJB-l) of the colonial cyanobacterium Microcystis aeruginosa from Lagoa das Gan;as, Sao Paulo, was cultured under non-axenic conditions. Exponential phase cells were harvested, concentrated and lyophilized for mouse bioassays and toxin extraction. The LDlOO oflyophilized cell suspensions was approximately 31 mg kg1 (dry cell weight/animal weight). Isolation, purification and characterization of the toxins were carried out by reversed phase HPLC, HPLC amino acid analysis and fast atom bombardment mass spectrometry. Strain NPJB­ 1 produces two different hepatotoxic heptapeptide microcystins. The main one was microcystin-LR, the most commonly reported microcystin from cyanobacteria. The other was microcystin-LF, the phenylalanine variant of microcystin-LR. This is the first published report for microcystin-LF. Introduction D-erythro-,8-methylaspartic acid, and Mdha is N­ I methyldehydroalanine (Carmichael et aI., 1988a). Several cyanobacterial genera and species (blue-green Adda, (2S, 3S, 8S, 9S)-3-amino-9-methoxy-2,6,8­ algae) that form water blooms in fresh and brackish trimethyl-1O-phenyldeca-4,6-dienoic acid, is the water bodies, produce potent hepatotoxic andlor neu­ remarkable structural feature of these toxins which rotoxic compounds. These are responsible for repeated confers toxicity (Rinehart, 1988; Harada et al., 1990a, cases of animal and human poisoning in many areas b). Although there are no confirmed poisonings of ani­ of the world (Carmichael et aI., 1988b; Sivonen et al., mals or humans by cyanobacterial blooms in Brazil, 1990; Lawton & Codd, 1991). decreasing water quality and increasing eutrophication Acute hepatotoxicosis associated with hepatotox­ of natural freshwater supplies and reservoirs has led ins is the most commonly encountered toxicosis to toxigenic cyanobacteria becoming dominant. This involving cyanobacteria. The colonial species Micro­ problem is intensified due to most Brazilian water sup­ cystis aeruginosa is the most common hepatotoxic plies having the environmental characteristics neces­ cyanobacterium in eutrophic freshwaters (Carmichael, sary for cyanobacterial growth during the entire year. 1992). Species and strains ofMicrocystis produce more These include high light intensity, high nutrient con­ than 40 types of related cyclic peptides called micro­ centrations, water temperatures betweel1 15 to 30°C cystins (Sivonen et aI., 1992). and little water movement (Beasley et aI., 1989). The general structure of microcystins is cyclo(­ The potential for human intoxication becomes D-Ala-X-D-MeAsp-Z-Adda-D-Glu-Mdha-), where X greater since the most _common cyanobacterium in and Z are variable L-amino acids, D-MeAsp is eutrophic Brazilian lakes and reservoirs is M. aerug­