Harmful cyanobacterial blooms and their negative impacts on water ecosystems and human health have been reported all over the world,and M.aeruginosa is one of the most dominant and ecologically damaging species in eutrophic lakes such as Dianchi Lake and Taihu Lake in China.Although physical and chemical control of the blooms is possible,these methods produce other problems.Thus,there is still a need for research on biological factors controlling cyanobacteria blooms,especially in shallow lakes.We screened part of the Yunnan University actinomycete strain library and found that the extract ofStreptomyces hebeiensis YIM 001T exhibited strong algicidal activity against M.aeruginosa.The main component-nanaomycin A methyl ester (NAME) was isolated at a level of 20 mg/L by large scale fermentation.Lytic mechanism experiments ofNA ME on Microcystis aeruginosa demonstrated it could effectively inhibit the growth of Microcystis aeruginosa (ECs0 at 72 h ≈ 3.0 mg L-1),hinder cell division and enlarge cell size.Nanaomycin A damaged M.aeruginosa cells as evidenced by decreases in algal activity,biomass,esterase activity and chlorophyll-a content.The SOD activity of the treated cells initially increasod,and then decreased together with a gradual increase in both O2-and malondialdehyde (MDA) content,consistent with inhibitory effects of NAME due to lipid peroxidation damage of the algal cell membrane.The results suggest that NAME may be effective for controlling undesired algae.