First report of microcystin production by picoplanktonic cyanobacteria isolated from a northeast Brazilian drinking water supply

Seven strains (NPCA-5, -10, -15, -16, -19, -23, and -29) of picoplanktonic cyanobacteria from Caruaru reservoirs were identified and analyzed for toxicity. We tested the toxicity of these strains by mouse bioassay, by HPLC, and by enzyme-linked immunosorbent assay (ELISA). Strains NPCA-15 and -23 were toxic when tested by mouse bioassay (LD100=600 mgDW/kg body weight). The toxin from strain NPCA-15 had the same UV spectrum as microcystin-LR. All of the strains showed the presence of microcystin by ELISA analysis. The microcystin concentration varied between 0.08 ng/mgDW (NPCA-5) and 3.7 ng/mgDW (NPCA-15). Confirmation of microcystin production by picoplankton opens the possibility that these organisms may have contributed to human poisoning in Caruaru and defines a new source of microcystin in water supplies. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 31–35, 1999