Colorimetric test for the monitoring of microcystins in cyanobacterial culture and environmental samples from southeast - Brazil

Microcystins are hepatotoxic heptapeptides produced by some cyanobacterial genera under determined physico-chemical conditions in the environment, which are responsible for the intoxication and death of animals and humans. The detection of microcystins in potable water or recreational water is not carried out routinely in the majority of Brazilian states. The protein phosphatase 1 (PP1) inhibition test is a simple, rapid and reproducible colorimetric method. The applicability of the PP1 inhibition test was tested using Microcystis aeruginosa (strain 1, UFRJ-toxin producer) grown under controlled light and temperature condition (12/12h light/dark using 30 mu E. m(2). s(-1) at 23 degrees C) in a bioreactor. The total concentrations of P (24, 6 and 4 mu M) and Fe (4 and 1 mu M) were varied in ASM-1 medium and their effects on the growth rates and toxin production were analyzed. A standard curve of PP1 inhibition by microcystin-LR reached detection limit of 0.01 ng. mL(-1). Under the highest concentrations of P (24 M) and Fe (4 M), the production of microcystin was detected throughout the growth experiment. The highest concentration of microcystin was observed at 6 mu M P while at 1 mu M Fe, PP1 inhibition was not detected. Samples from environmental blooms in water reservoirs used for human and animal consumption, from southeast Brazil (Belo Horizonte/MG), were tested and quantified for microcystin presence by the PP1 colorimetric test. The concentration of microcystin varied from undetectable to 100 ng. mL(-1) in the environmental samples with Microcistis flos-aquae as the predominant cyanobacterial strain.