Experimental evidence for the role of heterotrophic bacteria in the formation of Microcystis colonies
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Microcystis, a genus of cyanobacteria that is dominant in eutrophic lakes, occurs mainly as colonial morphs under natural conditions but as single cells in laboratory cultures. Recent studies have suggested that Microcystis–bacteria interactions significantly influence Microcystis morphology, but the underlying mechanism remains unclear. In this study, a total of 48 strains of heterotrophic bacteria were purified from Microcystis mucilage. Five bacteria, Aeromonas veronii, Enterobacter aerogenes, Exiguobacterium acetylicum, Bacillus cereus and Shewanella putrefaciens, can induce unicellular Microcystis to form colonies. Heterotrophic bacteria stimulated Microcystis growth and induced the production of extracellular polymeric substances in coculture treatments. Extracellular polymeric substances, such as extracellular polysaccharides (EPS), were responsible for the mucilage formation in colonial Microcystis. We analysed extracellular metabolic compounds produced by Microcystis aeruginosa and Microcystis wesenbergii using gas chromatography mass spectrometry. Filtrate extracts from coculture treatments indicated that some compounds, such as 2-dodecen-1-yl(-) succinic anhydride and benzoic acid, 2,3-bis[(trimethylsilyl)oxy]-, trimethylsilyl ester, might play a significant role in colonial M. aeruginosa or M. wesenbergii formation. Our data suggested that the interaction of Microcystis and heterotrophic bacteria was crucial for the formation of Microcystis colony and outbreak of Microcystis blooms.
KeywordsMicrocystis Associated bacteria Colony formation Extracellular polysaccharides Metabolic compounds
We thank Dr. J. S. Owen for his constructive suggestions and professional editing, Mr Liang Chen for his help in revising the manuscript, and Dr. Yuan Niu and Juan Lin for their help in sample preparation. This study was supported by the National Natural Science Foundation of China (31400407), the National High Technology Research and Development Program of China (Grant no. 2012ZX07105-004) and State Key Laboratory of freshwater ecology and biotechnology (2014FB15 and 2014FBZ02).
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