Impacts of different extracellular polysaccharides on colony formation and buoyancy of Microcystis aeruginosa

Tightly cell-bound extracellular polysaccharides (TB-EPS) enhanced colony formation of Microcystis aeruginosa NIES-843, which is strictly related to buoyancy. Microscope observation shows the colony induced by TB-EPS likes wild Microcystis. Temperature and light affected colony formation and buoyancy. On the surface of Microcystis cells, there is a carbohydrate called extracellular polysaccharides (EPS) playing a significant role in the colony formation of Microcystis. EPS consists of tightly cell-bound EPS (TB-EPS), and both of these substances are considered to be strongly related to the colony formation and buoyancy of Microcystis. In this study, Microcystis aeruginosa (strain: NIES-843) was used to examine the effects of EPS, TB-EPS, and divalent metal cations such as calcium and magnesium on the buoyancy and colony formation of M. aeruginosa NIES-843. Under various light conditions, the addition of TB-EPS into the culture medium induced M. aeruginosa NIES-843 to obtain high buoyancy at concentrations of Ca2+ and Mg2+ concentrations of 10 mg/L and 30 mg/L, respectively. Under the absence of light, the addition of EPS could lead M. aeruginosa to form a colony and obtain buoyancy, and the addition of TB-EPS could not significantly change the buoyancy of M. aeruginosa NIES-843. The colony size analysis showed that at the same cationic concentration, the addition of TB-EPS could induce M. aeruginosa to form the largest colony and present strong buoyancy. This study suggested that temperature and illumination are conducive to colony formation and present higher buoyancy of M. aeruginosa.