Physiological responses of Microcystis aeruginosa under the stress of antialgal actinomycetes

Eutrophication has occurred frequently in various lakes and reservoirs, and the metabolic excretion produced during the algae growth causes serious water pollution and threatens ecological security. Biological control approaches such as screening bacteria with the capability to degrade cyanobacteria are an environment-friendly way. An isolated antialgal strain Streptomyces sp. KY-34, was applied to degrade the cyanobacterium Microcystis aeruginosa, and the possible biodegradation mechanism was investigated. The results showed that the fermentation liquor of Streptomyces sp. KY-34 could inhibit the growth of M. aeruginosa by restrained the synthesis of chlorophyll and photosynthetic pigments, and decreasing the contents of cellular protein and non-protein, accordingly led to the increase of malondialdehyde content, and the activities of superoxide dismutase, catalase and peroxidase in algae cells. In addition, the variation of the cellular ultrastructure indicated a serious change in algal physiology. It's revealed that the biodegradation mechanism of M. aeruginosa should primarily be that Streptomyces sp. KY-34 caused the damage of algae cell membrane and led to the increases of antioxidant enzymes, and then the growth of M. aeruginosawas inhibited.