Selection and characterization of plant-derived alkaloids with strong antialgal inhibition: growth inhibition selectivity and inhibitory mechanism

In recent years, researches on microalgae inhibition with plant-derived active substances have attracted much attention. In this study, the inhibition of six plant-derived alkaloids (neferine, isoliensinine, linensinine, nuciferine, capsaicin, and hordenine) on bloom-forming cyanobacteria Microcystis aeruginosa were investigated. The results showed that neferine and nuciferine had stronger inhibition on the growth of M. aeruginosa compared with the other four alkaloids, and the relative inhibition rate reached 91.27% and 88.70% at the concentration of 4.5 mg/L after 7 d of exposure, respectively. Different from neferine, nuciferine has no inhibition on Chlorella sp. and Tetradesmus obliquus. It also increased the diversity and species homogeneity of phytoplankton in the environmental water samples. Nuciferine decreased the contents of chlorophyll a and β-carotene in M. aeruginosa with the extension of treatment time, which was 59.40% and 31.90% of the control at the concentration of 1.04 mg/L after 48 h, respectively. After 48 h of nuciferine exposure, the values of fluorescence parameters including maximum quantum yield (Fv/Fm), actual quantum yield of PSII (Yield), non-photochemical quenching (qN and NPQ), and electron transport rates (ETR) of M. aeruginosa cells were significantly decreased and photosynthetic capacity was weakened. The superoxide dismutase (SOD), catalase (CAT), ascorbic acid (ASA), and glutathione (GSH) in the cells were significantly reduced, and the hydrogen peroxide (H2O2) and malonaldehyde (MDA) contents continued to accumulate, causing severe oxidative damage. Therefore, the good biological safety and strong specific inhibition of nuciferine makes it have great application prospects in the inhibition of cyanobacteria blooms.