Effect of sonication on live and fixed cells of Microcystis aeruginosa

Sonication has been used in many studies that require observation of the cells of Microcystis aeruginosa. This study investigates the extent to which sonication (42 kHz, 150 W) destroys live and Lugol-fixed cells of M. aeruginosa, using two strains (NIES-1090 and NIES-1157). Live cells were easily destroyed by sonication regardless of growth stage. Sonication for 50 s caused up to 32.8% (NIES-1090) and 40.8% (NIES-1157) cell losses, and extended sonication (250 s) destroyed more cells. In contrast, sonication did not cause loss of cells that had been fixed with Lugol’s iodine solution. Interestingly, sonication often resulted in slightly higher counts of Lugol-fixed cells under a microscope. Sedimentation of Lugol-fixed cells is enhanced after sonication owing to the collapse of gas vacuoles and this appeared to facilitate reliable microscopic observations.