Nanaomycin A methyl ester, an actinomycete metabolite: Algicidal activity and the physiological response of Microcystis aeruginosa

Harmful cyanobacterial blooms and their negative impacts on water ecosystems and human health have been reported all over the world, and Microcystis 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 or chemical control of the blooms is possible in short period, these methods could cause other problems. Thus, there is still a need for research on biological factors controlling cyanobacteria blooms. We screened part of the Yunnan University actinomycete strain library and found that the extract of Streptomyces hebeiensis YIM 001(T) exhibited obvious inhibition on M. aeruginosa. The main component - nanaomycin A methyl ester (NAME) was isolated at a level of 20 mg L-1 by scale-up fermentation. Lytic mechanism experiments of NAME on M. aeruginosa demonstrated it could effectively inhibit the growth of M. aeruginosa (EC50 at 72 h = 2.97 mg L-1), hinder cell division and enlarge cell size. NAME 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 increased, and then decreased together with a gradual increase in both O-2(-) 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 is effective for controlling undesired cyanobacteria and the Chl-fluorescence is a potential endpoint to assay the NAME eco-toxicity on cyanobacteria. (C) 2012 Elsevier B.V. All rights reserved.