Effects of mixing intensity on colony size and growth ofMicrocystis aeruginosa

Mixing is an integral environmental factor that affects lake ecosystems. For the cyanobacteriumMicrocystis, colony size is important with respects to migration velocity, how cells respond to grazing pressure, light attenuation, nutrient uptake and growth. To understand how mixing shapes colony size and the growth ofMicrocystis, we measured the effects of different current velocities (0, 0.16, 0.32, 0.64, and 1.28 m s−1) onM. aeruginosain Lake Taihu. After 24 h of continuous mixing, the mean colony sizes ofM. aeruginosain the controls, 0.16, 0.32, 0.64, and 1.28 m s−1groups were 23.6, 50.1, 92.9, 67.8, and 37.3 μm, respectively. Colony sizes ofM. aeruginosain all treatment groups were significantly larger than those in controls. As well, the concentration of soluble extracellular polysaccharide and bound extracellular polysaccharides ofM. aeruginosain all treatment groups were significantly higher than those in controls. Except for the highest level of mixing (1.28 m s−1), the growth rate ofM. aeruginosawas significantly higher than that in controls. This study suggested that mixing intensity over short time periods can significantly influence colony size and the growth ofM. aeruginosa.