Algicidal activity and potential mechanisms of ginkgolic acids isolated from Ginkgo biloba exocarp on Microcystis aeruginosa

Natural plant agents are considered promising sources to control harmful algal blooms. The primary purpose of this study was to isolate the algicidal compounds from Ginkgo biloba exocarp against the toxic cyanobacterium Microcystis aeruginosa and determine the potential inhibition mechanisms. Bioassay-guided fractionation of petroleum ether extract yielded ginkgolic acids, which were identified by spectral analysis (infrared and reversed-phase high-performance liquid chromatography/electrospray mass spectrometry). Bioassays showed ginkgolic acids inhibited M. aeruginosa growth effectively with the 3- and 7-day median effective concentration (EC_50,3d, EC_50,7d) of 3.26 and 2.03 mg L^?1, respectively. For the potential inhibition mechanisms, cellular morphology, physiological changes, and genes expression during 12–96 h of exposure were investigated. Ginkgolic acids caused morphologic damage or lysis of cells. They induced oxidative damage by increasing malondialdehyde content and decreasing total antioxidant and superoxide dismutase activities. Transcription of three photosynthetic genes (psaB, psbD, and rbcL) and two nutrient uptake related genes (ntcA and phoU) were also found to be inhibited. Additionally, ginkgolic acids also affected the microcystin contents and the transcription of microcystin-related genes. The results suggested that ginkgolic acids isolated from G. biloba exocarp have the potential to inhibit M. aeruginosa growth effectively by causing pleiotropic effects on several physiological and biochemical reactions.