Study On Allelopathic Effect Between Microcystis Aeruginosa And Microcystis Wesenbergii

Cyanobacteria bloom has been becoming one of the most serious environmental problems in China. The formation of cyanobacteria bloom is often accompanied by the succession of different algae. Studing the allelopathic effect among different cyanobacteria and its contribution in competition process and identifying potential allelochemicals can provide important theoretical basis on the mechanism of the succession of dominant cyanobacteria species and cyanobacteria bloom-forming.Microcystis aeruginosa and Microcystis wesenbergii are two common cyanobacteria species in the eutrophic shallow lakes in China. In laboratory, allelopathic effect between the two cyanobacteria was studied by co-cultivation and cultivation with cell-free filtrates. The co-cultivation experiment showed that the mutual inhibition effect took place between them. M. wesenbergii was inhibited strongly due to the allelopathic effect from M. aeruginosa, and M. aeruginosa was also stressed slightly. When the initial cell density of both algae was more than0.5x106cells-mL-1, the inhibition rate of M. wesenbergii was more than80%after9days cultivation. Meantime, the growth of M. wesenbergii was also inhibited by adding cell-free filtrates from M. aeruginosa in exponential phase. M. wesenbergii was restrained significantly (p<0.01) when the initial cell density of M. wesenbergii was less than0.5x106cells-mL-1and the filtrates were added continuously into the culture solution. On the contrary, the growth of M. aeruginosa was promoted by adding cell-free filtrates from M. wesenbergii.The cell-free filtrate of M. aeruginosa was extracted by HLB-SPE column. The different extracts were obtained by eluting with n-hexane, dichloromethane and methanol in turn. The extracts were used for algicidal bioassay with M. wesenbergii and qualitative analysis with GC-MS and LC-MS. The results showed that the higher polarity the eluting solvents were, the stronger allelopathic effect of the extracts were, and the methanol extract had the strongest inhibtion activity to M. wesenbergii. Microcystin-LR, a potential allelochemical, was identified by HPLC and LC-MS in the methanol extract. Another potential allelochemical, was detected in the extract of dichloromethane, its molecular weight was678.5, but its chemical structure needed further research.