Control of the Buoyancy of Microcystis aeruginosa Via Colony Formation Induced by Regulating the Amount of Extracellular Polysaccharides and Cationic Ions

摘要

In recent years, with deepening lake eutrophication and the excessive discharge of domestic wastewater and industrial effluent, cyanobacterial blooms, mainly composed of the genus Microcystis (Microcystis blooms), have become more frequent in eutrophic lakes. It is well recognized that gas vesicles and colony formation strongly influence the buoyancy of Microcystis and control the migration in the water column. Although some of Microcystis stains do not synthesize gas vesicles in the cell, Microcystis, especially wild strain, exhibits strong buoyancy. In this study, to clarify investigate the relationship between colony formation and buoyancy, the non-gas vesicle-synthesizing stain M. aeruginosa UTEX-2061 and the gas vesicle-synthesizing stain M. aeruginosa NIES-843 were used for the buoyancy experiment. With the addition of the extracellular polysaccharides (EPS) extracted from Microcystis blooms to the culture medium, both M. aeruginosa NIES-843 and UTEX-2061 could exhibit higher buoyancy with the presence of cationic ions, and the colony size expansion was also observed. By inducing colony formation and calculating the relative buoyancy rate of each strain, it was proven that the colony formation strictly related to the buoyancy of both Microcystis strains.