No abstract

Toxicity of cyanobacteria is the subject of ongoing research, and a number of toxic metabolites have been described, their biosynthesis pathways have been elucidated, and the mechanism of their action has been established. However, several knowledge gaps still exist, e.g., some strains produce hitherto unknown toxic compounds, while the exact dynamics of exerted toxicity during cyanobacterial growth still requires further exploration. Therefore, the present study investigated the toxicity of extracts of nine freshwater strains of Aphanizomenon gracile, an Aphanizomenon sp. strain isolated from the Baltic Sea, a freshwater strain of Planktothrix agardhii, and two strains of Raphidiopsis raciborskii obtained from 25- and 70-day-old cultures. An in vitro experimental model based on Cyprinus carpio hepatocytes (oxidative stress markers, DNA fragmentation, and serine/threonine protein activity) and brain homogenate (cholinesterase activity) was employed. The studied extracts demonstrated toxicity to fish cells, and in general, all examined extracts altered at least one or more of considered parameters, indicating that they possess, to some degree, toxic potency. Although the time from which the extracts were obtained had a significant importance for the response of fish cells, we observed strong variability between the different strains and species. In some strains, extracts that originated from 25-day-old cultures triggered more harmful effects on fish cells compared to those obtained from 70-day-old cultures, whereas in other strains, we observed the opposite effect or a lack of a significant change. Our study revealed that there was no clear or common pattern regarding the degree of cyanobacterial bloom toxicity at a given stage of development. This means that young cyanobacterial blooms that are just forming can pose an equally toxic threat to aquatic vertebrates and ecosystem functioning as those that are stable or old with a tendency to collapse. This might be largely due to a high variability of strains in the bloom.

The ecological potential of microalgae for purification of aquatic and soil ecosystems and natural restoration of their homeostatic functional state is considered to be high due to the rapid growth and development of algae, their labile and dynamic metabolism and simple growth conditions. The aim of present work was to study the effectiveness of Chlorella as a potential bioremediator to reduce the toxic effects of pesticides, roundup and chlorpyrifos after their individual and complex influence on zebrafish Danio rerio. The effect of environmental concentrations of roundup (15 μg⋅L-1) and chlorpyrifos (0,1 μg⋅L-1) provoked partial depletion of the cell thiols pool when compared to the control, which appeared as a decrease in glutathione transferase activity (under combined exposure) and total glutathione concentration. A decrease in the level of total antioxidant capacity, which was consistent with an increase in the level of reactive oxygen species in the liver tissue was also shown. Meanwhile, the studied organophosphate pesticides didn’t cause severe signs of neurotoxicity, but activated acetylcholinesterase in line with no visual manifestations of locomotion reactions. Chlorpyrifos determined an increase in the concentration of methylglyoxal and the most noticeable sign of endocrine disruption from all studied groups in terms of vitellogenin concentration. Principal component analysis allowed to identify a separate localization of each of the studied groups and the interim position of animals after combined exposure when compared to the individual action. The introduction of Chlorella vulgaris in the exposure media in the amount of about 100 thousand cells / dm3 did not show a significant corrective effect on the toxicity of pesticides for non-target species Danio rerio, which doesn’t exclude the positive impact of algae on the functioning of the ecosystem in general and requires a more detailed analysis.