The Effect of Ultrasound on Microcystis sp. Morphological Characteristics at Different Ultrasonic Power

Optical microscope, environmental scanning electron microscope (ESEM) and transmission electron microscope (TEM) were applied to study the effect of different intensity ultrasound on Microcystis cell morphology. The results showed that after the action of low intensity ultrasound (below the cavitation threshold) on Microcystis cell, extracellular surface became slightly rough, and gelatinous sheath became uneven. Fragmented debris appeared among cells and intracellular thylakoids and bubbles were damaged. Low intensity ultrasonication make photosynthetic capacity and buoyancy control ability of the cell suppressed or disappeared, leading to the inhibition of growth. The main mechanism of low intensity ultrasound on Microcystis cell was mechanical action. After ultrasonication of high intensity, extracellular surface was paler and rough. Gelatinous sheath became more uneven, and there were many fragmented debris. Cell interior was black. All of thylakoids and bubbles were broken, dissolved and disappeared. Cells present as partial block or homogenized structure. Some algal cells appeared pyknotic, but most cell were dead. The main mechanism of high intensity ultrasound was cavitation effect, accompanied by mechanical action at the same time.