| dc.description.abstract | Cyanobacteria can produce highly potent cyanotoxins, however, limited information is provided about their
toxicity mechanisms in exposed aquatic invertebrates at the molecular level. In the present study, the effects of
cyanobacterial strains from the genus Nostoc (Nostoc Z1 and Nostoc 2S3B) in Daphnia magna after waterborne
exposure were investigated. Examined endpoints included immobilization (survival) in acute toxicity tests and
selected gene expression changes (cyp314, cyp360A8, gst, p-gp, vtg) analyzed by the quantitative real-time polymerase
chain reaction (RT-PCR). In addition, enzyme-linked immunosorbent assay (ELISA) was performed to
determine whether the observed changes could be due to the presence of microcystins, the most widespread
group of cyanotoxins. The results of acute toxicity tests have shown only minor changes in survival rates, which
have not exceeded 20% after 48 h of exposure to either strain. On the other hand, significant changes were
recorded in molecular responses of Daphnia to tested strains. Treatment with the aquatic strain Nostoc Z1 altered
the expression levels of all analyzed genes. Both strains caused a significant p-glycoprotein (p-gp) induction at 75
μg ml 1 which suggests the involvement of p-gp mediated multixenobiotic resistance mechanism (MXR) in
facilitating excretion of toxic cyanobacterial compounds in daphnids. Additionally, these strains caused an increase
in the expression levels of cyp360A8, indicating that genes related to detoxification processes could be
sensitive indicators of cyanobacterial toxicity. Statistically significant induction of cyp314, as well as increases in
expression of gst and vtg, were observed only after exposure to Nostoc Z1. This study indicates the potential of
certain cyanobacterial metabolites to modify the expression of toxicant responsive genes involved in phase I and
phase III of the xenobiotic metabolism, as well as possible interference with growth and reproduction in
D. magna. Low microcystin concentrations found in both samples suggest that these cyanotoxins were not
responsible for the detected toxic effects. | en_US |
