Antioxidant responses of microalgal species to pyrene

The antioxidant response of four freshwater microalgal species, Chlorella vulgaris Beij., Scenedesmus platydiscus (G. M. Smith) Chod., Scenedesmus quadricauda(Turp.) Bréb., and Selenastrum capricornutum Printz without pyrene addition (control) and at two pyrene concentrations (0.1 and 1.0 mgL⁻¹) were investigated. Under the control condition, the values of the antioxidant parameters differed significantly among species and the difference was seemed not to be related to their susceptibility to pyrene. The antioxidant response to pyrene treatments also varied from species to species. Pyrene led to a significant increase in total glutathione (GSH) content in all species except C. vulgaris, a species did not exhibit any ability to metabolize pyrene. The glutathione-S-transferase (GST) activities also remained unchanged in pyrene treated C. vulgaris, increased greatly in S. platydiscus and Se. capricornutum (the two species with higher pyrene metabolism ability), but inhibited remarkably in S. quadricauda (the only species sensitive to pyrene toxicity). On the other hand, the glutathione reductase (GR) activities increased in C. vulgaris but remained at a similar level as the control in the other three species. The malondialdehyde (MDA) content, an indicator of lipid peroxidation, declined in S. quadricauda but showed no significant change in the other three species. The activities of glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) in pyrene treated cells remained almost the same as the controls for all microalgal species. Results suggested that the alterations of antioxidant systems in microalgae might not be useful indicators of pyrene exposure but pyrene-enhanced GSH metabolism might be important in pyrene biotransformation.