Antioxidant responses of two microalgae, Selenastrum capricornutum and Chlorella sp., to estradiol and ethinylestradiol

The cellular characteristics and antioxidant responses including reactive oxygen species (ROS), esterase activity, superoxide dismutase, peroxidase (POD), glutathione (GSH), and malondialdehyde (MDA) content of two microalgal species, Selenastrum capricornutum and Chlorella sp., exposed to single and mixed estradiol (E2) and ethinlyestradiol (EE2) at a final concentration of 200 μg L^?1 were investigated. The growth, autofluorescence, cell complexity, and cell size of S. capricornutum and Chlorella sp. were not affected by single and mixed estrogen treatments, but the temporal trends of these two species were different. The temporal changes of the esterase activity and ROS level in these two species were also very different, with a continuous increase with time in Chlorella but peak on Day 2 in S. capricornutum. The esterase activity of S. capricornutum was not affected by estrogen treatments; however, the activity in treated Chlorella decreased significantly from Day 2 onwards. The single EE2 and mixed E2 and EE2 treatments induced more ROS of S. capricornutum than the single E2 treatment and control on Day 4, but no other difference was found between treatments and control of Chlorella on that day. The other oxidative damage responses of S. capricornutum were not affected by estrogen treatments, except MDA increased in EE2 treatment, on the other hand, POD and GSH of Chlorella increased in both single and mixed estrogen treatments on Day 4. These results suggested that microalgae species were tolerant to E2 and EE2, but some species-specific changes occurred to combat the oxidative stress posed by estrogens.