Gene expression changes in Daphnia magna following waterborne exposure to cyanobacterial strains from the genus Nostoc

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.