The Effect of pH and Light on the Colony Formation and Buoyancy of Microcystis aeruginosa UTEX-2061

Extracellular polysaccharides (EPS) in the outer layer of Microcystis cells can influence colony formation and buoyancy ability. The carboxyl groups in EPS can combine with divalent metals to induce colony formation. One of the main components in EPS is called tightly cell-bound EPS (TB-EPS), which contains more carboxyl groups and potential to combine with more metal ions. In this study, we isolated the EPS and TB-EPS from Microcystis bloom sample, and, using both EPS samples, the effect of EPS and TB-EPS on the colony formation and buoyancy of M. aeruginosa UTEX-2061 was investigated. Then, we discussed the impact of the environmental factors such as light and solution pH on M. aeruginosa UTEX-2061 colony formation and buoyancy. With the addition of Ca2+, Mg2+, EPS, and TB-EPS, M. aeruginosa UTEX-2061 could form a colony, in which the size was more than 200 mu m, showing the same strong buoyancy as wild Microcystis. The addition of TB-EPS could lead to M. aeruginosa UTEX-2061 to form the largest colony and exhibit strong buoyancy under light conditions. Under dark conditions, the addition of EPS or TB-EPS failed to lead M. aeruginosa to form a colony and obtain buoyancy, indicating that light affects colony formation and buoyancy. The solution pH played a role in controlling colony formation and buoyancy. Neutral conditions (pH 7) were conducive for TB-EPS to induce colony formation, while under alkaline conditions (pH 10), EPS had an excellent effect on the induction of M. aeruginosa UTEX-2061 colony formation.