Effects of toxic and non-toxic crude extracts on different Microcystis species (Cyanobacteria)

Our objective was to investigate crude extracts toxic (MC+) and non-toxic (MC-) effects on the growth of Microcystis panniformis, Microcystis aeruginosa and Microcystiswesenbergii. Cultures were submitted to extracts MC+ at 5 and 10 MC µg.L-1, and to MC- equivalent weight of these concentrations. Both crude extracts worked toward reducing the growth of M. wesenbergii and stimulating the growth of M. panniformis. Likewise, M. aeruginosa was inhibited by addition of crude MC- extract. The action of microcystins at concentrations commonly found in natural environments, plus the presence of other substances in intracellular M. aeruginosa produced differentiated effects in Microcystisspp.   Key words: Microcystis aeruginosa, Microcystis panniformis, Microcystis wesenbergii, allelopathy, crude extract, microcystin, phytoplankton, toxin