Effects of Ca and Mg levels on colony formation and EPS content of cultured M. aeruginosa

Colony formation of Microcystis plays a significant role in Microcystis blooms. Calcium (Ca) and magnesium (Mg) are important nutrient elements during algae growth. In this study, the influences of Ca and Mg concentrations on extracellular polysaccharides (EPS) content and colony formation of Microcystis were investigated, and then the effects of EPS content and specific growth rate on colony formation were discussed. The results showed that Ca had a direct observable influence on the colony formation of Microcystis; however, Mg was not obvious. More specifically, when Ca concentration was lower than 20 mg•L-1, the Microcystis was dominated by single cells, when the concentration was over 20 mg•L-1, Microcystis colonies were found and took up more than 50%, and the size of colony was increased with the increasing Ca concentration. Moreover, it showed that the mean size of Microcystis had significant correlation with EPS content, and lower specific growth rate was in favor of colony formation.