Fig. 4

Effects of the screened metabolites on the algal cellular composition and infection process. A Degradation of the algal cellular components by the screened metabolites. The control and the mixture was the algal cells treated with BG11 medium and 10 reagents that mixed in equal volume, respectively. B Effects of the screened metabolites on the infection ratio. C Fe³⁺ reducing ability of 3-HAA and hordenine. D Production of hydroxyl radicals by hordenine and 3-HAA. E Relative intracellular ROS intensity of algal cells after treated with hordenine or 3-HAA, determined by DCFH-DA staining. The fluorescence intensity of the BG11 medium-treated algal cells (control) was considered as 100%. The concentration of cyclohexylamine was 2% (v/v), and the concentration of the other 9 reagents were 0.2% (w/v) in the assays. The solutions were prepared with the BG11 medium and heated in the 95 °C water bath for 15 min, followed by ultrasonic treatment for 5 min and filtrated with 3000 Da cut off membrane prior to use. The quantitative data were presented as mean ± S.D. (n = 3). *, p < 0.05, **, p < 0.01 (Student’s t test). The Fe³⁺ reducing ability and hydroxyl radical productivity of the other 8 metabolites can be referred to Figures S3 and S4 (Additional file 1)