Cyanobacterial blooms are undesirable for ecological and health reasons. While Woronichinia naegeliana is a cyanobacterial species that appears frequently in freshwater, information about it is limited. An evaluation of its toxicity was conducted via tests based on the crustaceans Thamnocephalus platyurus and Daphnia pulex. The greatest effect of the aqueous extract obtained from W. naegeliana cells was observed for T. platyurus. The denoted semi-lethal concentration (LC50) after 24 h of exposure was 0.99 mg of dry weight (d.w.) mL-1. A lower toxicity was displayed for D. pulex, although it grew with time. Among the 18 fractions separated from cyanobacterial extract, only one containing the microginin FR3 (MG-FR3) displayed biological activeness against T. platyurus. The remaining products synthesized by W. naegeliana displayed an absence or a low level of toxicity making it impossible to determine the LC50 value. Detailed research revealed that MG-FR3 did not affect the activity of enzymes such as trypsin, chymotrypsin, elastase and thrombin, which indicates another mode of action. The results demonstrated that blooms of W. naegeliana showed toxic activity towards invertebrate zooplankton.
Keywords: Bioassays; Cyanobacteria; Cyanopeptides; Microginins.