Effects of temperature on the buoyancy of Microcystis aeruginosa

Microcystis aeruginosa were cultured in different temperature: 10°C, 15°C, 20°C, 25°C, 30°C to screen the effects of temperature on buoyancy regulation. Cell density was measured by percoll density gradient centrifugation and cell buoyancy was calculated by the buoyancy formula. Simultaneously, biomass, specific growth rate, the photosynthetic activity, the activity of NAD (P) H dependent oxidoreductase, intracellular carbohydrate, protein content, the percentage of floating cells were measured. With the increasing of the experimental temperature (10°C-30°C), buoyancy, the percentage of floating cells, intracellular protein content, photosynthesis rate and the activity of NAD (P) H dependent oxidoreductase increased and the intracellular carbohydrate content decreased. After 7 days cultured at 10, 15°C, cell density were increased by 2.7% and 1.3%, respectively; carbohydrate content were increased by 95.3% and 65.5%, respectively; the percentage of floating cells were reduced by 23.8% and 18.3, respectively; the activity of NAD (P) H dependent oxidoreductase were reduced by 23.8% and 18.3% respectively. After 7 days cultured at 20, 25, 30°C, cell density were reduced by 2.8%, 3.8% and 3.2%, respectively; carbohydrate content were reduced by 8.5%, 2.9% and 19.4%, respectively; the percentage of floating cells were increased by 0%, 7% and 8.5%, respectively; the activity of NAD (P)H dependent oxidoreductase were increased by 0%, 7% and 8.5%, respectively. It was concluded that cell growth rate, photosynthetic rate, metabolic rate were the function of temperature in the buoyancy regulation of Microcystis aeruginosa. The main reason for the buoyancy loss is the accumulation of carbohydrate, the temperature threshold value for the buoyancy is between 15~20°C.