Identification of Compounds with Allelopathy on Bloom Microalgae from the Secondary Metabolites of Endophytic Fungi Isolated from Marine Macroalgae and the Algicidal Activities

To obtain compounds with allelopathy on bloom microalgae, 28 strains of marine macroalgae-endophytic fungi were tested, and four strains in which crude extracts of the secondary metabolites showed apparent allelopathy on Anabaena flos-aquae and Microcystis aeruginosa were obtained. The four strains were cultured in 15 L of PDB culture and the algicidal activities of 32 compounds isolated from the secondary metabolites were examined. The inhibition ratios of sterigmatocystin, (2'E,4'E,6'E)-6-(1'-carboxyocta-2',4',6'-triene)-11,12-epoxy-9,11-dihydroxydrim-7-ene, 6,8-di-O-methylnidurufin and aversin on A. flos-aquae were all significantly higher than 50% (P < 0.05), and the EC_50,24h values were 6.865 μg/mL, 4.302 μg/mL, 1.824 μg/mL and 2.319 μg/mL, respectively. The inhibition ratios of sterigmatocystin,(2'E,4'E,6'E)-6-(1'-carboxyocta-2',4',6'-triene)-11,12-epoxy-9,11-dihydroxydrim-7-ene and indol-3-carboxaldehyde on M. aeruginosa were all significantly higher than 50% (P < 0.05), and the EC_50,24h values were 4.167 μg/mL, 8.386 μg/mL and 5.374 μg/mL, respectively.