Control of Microcystis Buoyancy by Reducing Cellular Carbohydrate Content at High Temperature

Abstract

This study aimed to control the buoyancy of Microcystis by increasing the growth rate and simultaneously reducing the cellular carbohydrate content under various light and temperature regimes. Microcystis was precultured in continuous dark (0 µmol·m−2·s−1) or light conditions (135 µmol·m−2·s−1) for 48 hours at 30°C and 35°C. After preculture, Microcystis was cultivated in a burette to observe the difference in the buoyancy. The buoyancy was evaluated by relative buoyancy of 25% (RB25), defined as the percentage of Microcystis cell number in the upper 25% layer to the total cell number in the burette. The result showed that preculture under the dark condition at 30°C had higher RB25 (43.8 ± 3.5%), than under the light condition (23.8 ± 2.8%). In addition, Microcystis precultured in the dark condition at 30°C also had the lowest cellular carbohydrate (3.1 ± 0.3 pg/cell). The reduction of cell ballast would promote the buoyancy of Microcystis. These results indicate that the buoyancy of Microcystis can be controlled by reducing cellular carbohydrate using preculture under the dark condition at high temperature. Thus, artificial control to increase Microcystis buoyancy could be a useful method for removal of Microcystis blooms, especially in water purification plants.

Keywords

• microcystis blooms
• buoyancy control
• removal of blooms
• cellular carbohydrate
• light regimes