Buoyancy control of Microcystis using different light regimes combined with extracellular polysaccharides and cationic ions

ABSTRACT Cyanobacterial blooms are widely known to cause problems in the aquatic environment, and their appearance has become more frequent due to global warming. Microcystis is one of the most widespread and dominant bloom-forming cyanobacterial genera, largely because Microcystis has the ability to control its buoyancy. A buoyancy experiment conducted on Microcystis sp. isolated from cyanobacterial blooms in Lake Senba, Japan, showed that buoyancy could be controlled using a combination of preculture under the dark conditions and the addition of powdered tightly bound extracellular polysaccharides (TB-EPS) and metal cations (Ca2+ and Mg2+). Preculture under the dark conditions, 96 h in length were the most effective treatment to reduce the cellular carbohydrate content of Microcystis and simultaneously increase its buoyancy. The addition of TB-EPS, Ca2+ and Mg2+ ions increased the colony size of Microcystis and enhanced buoyancy in precultures under both dark and light conditions. Thus, the buoyancy of Microcystis can be controlled by reducing its cellular carbohydrate content by preculturing it in dark conditions for 96 h and increasing the colony size with the addition of 100 mg l−1 EPS, 80 mg l−1 Ca2+ and 80 mg l−1 Mg2+. This study contributes to establishing a novel removal method for cyanobacterial blooms dominated by Microcystis, especially in water treatment facilities. HIGHLIGHTS • Microcystis buoyancy was controlled by decreasing cellular carbohydrate content using preculture under dark conditions. • The addition of TB-EPS, Ca2+ and Mg2+ ions increased the colony size of Microcystis and enhanced the buoyancy in precultures under both dark and light conditions. • This represents a novel removal method for cyanobacterial blooms in water treatment facilities.