The inhibition mechanism and death mode of Microcystis aeruginosa induced by the continuous pressure of artemisinin sustained-release microspheres (ASMs)

Abstract

Artemisinin, a natural allelochemical substance extracted from Artemisia annua, has been shown to have strong inhibitory effects on harmful cyanobacteria. However, only a few studies have systematically studied the mechanism of artemisinin in inhibiting algae and the process of algae cell death. In this study, the inhibition mechanism and death mode of M. aeruginosa under artemisinin sustained-release microspheres (ASMs) were investigated using a series of morphological, physiological and biochemical characteristics. The findings revealed that M. aeruginosa was significantly inhibited immediately after exposure to the 0.54 g·L−1 ASMs, with an inhibition rate (IR) exceeding 95 %, and the synthesis of phycobiliprotein and esterase activity were disturbed. In addition, ASMs exposure significantly increased caspase-3(-like) activities of M. aeruginosa. Under the continuous stress of ASMs, M. aeruginosa cells had three cell death modes: the first was necrosis-like cell death, which was characterized by cell wall rupture and leakage of cell contents; the second was apoptosis-like cell death, which was characterized by the disintegration of the cell structure, the integrity of the cell membrane, and the appearance of apoptotic bodies; and the last was autophagy-like cell death, which was characterized by cell swelling and appearance of autophagy vacuoles. These results indicated that ASMs could inhibit photosynthesis of M. aeruginosa cells, interfere with its antioxidant mechanisms and activate caspase-3(-like) activity, resulting in programmed cell death (PCD).