Effects of microcystin-LR and nitrite on the lifespan, reproduction, and heat shock responses of rotifer Brachionus calyciflorus at different temperatures

Abstract

Cyanobacterial blooms aggravate with increasing temperature, and the increased concentrations of toxicants such as cyanotoxins and nitrite during bloom decay adversely affect the growth of aquatic animals. Heat-shock proteins (Hsps) are induced by a wide range of environmental stressors, including temperature and toxicants. In this study, Brachionus calyciflorus Pallas was exposed to different combined solutions of microcystin-LR (0, 10, 30, and 100 µg L−1) and nitrite (0, 1, 3, and 5 mg L−1) to evaluate their effects on the rotifer lifespan, the reproductive rate (R), and the responses of four Hsp genes at 20 °C, 25 °C, and 30 °C. Results revealed that single high doses of microcystin-LR (100 µg L−1) and nitrite (5 mg L−1) were harmful to the lifespan and reproduction of rotifers. Hormesis was induced by low doses of microcystin-LR (10–30 µg L−1) and nitrite (1–3 mg L−1). At different toxicant concentrations, the expression levels of Hsp40, Hsp60, Hsp70, and Hsp90 fluctuated, whereas reactive oxygen species (ROS) levels increased regardless of temperature. The two toxicants induced high levels of ROS production, which negatively affected the lifespan, R, and Hsp gene expression at 30 °C (p 0.05). Temperature, microcystin-LR, and nitrite had interactive effects on the lifespan, R, ROS levels, and Hsp gene expression levels (p < 0.05). The expression levels of Hsp genes are useful biomarkers of high-temperature exposure, and Hsp-mediated heat shock responses are important in microcystin-LR and nitrite stress tolerance of B. calyciflorus.