1. Journal of Applied Phycology 15: 37–43, 2003. Lab of Molecular biology of Cyanobacteria Tsinghua Univerisity Abstract:Results:Equipments: Effects of Ultrasonic Irradiation on Gas vesicles in Cyano- bacterial Cells and Related Physiological Properties Jiaowen Tang, Qingyu Wu*, Hongwei Hao Ultrasonic waves of high frequency (1.7 MHz) and low intensity (0.6W cm -2 ) were employed to prevent cyano- bacterial cells from growing fast and the mechanisms of this growth inhibition were investigated. Gas vesicles occur almost exclusively in cells of waterbloom-forming cyano-bacteria, which contain gas and provide cells with buoyancy. It is proposed that cavitation is a nonthermal mechanism of ultrasonic irradiation that occurs when the gas vesicles are acted upon by a sufficiently intense ultrasound beam of 1.7MHz. Free radical and sonochemical effects can arise when inertial cavitation occurs, which greatly affects passive membrane permeabilities, active transport processes, and metabolic rates. It was proposed that 1.7MHz ultrasonic irradiation is effective in preventing waterbloom-forming cyanobacteria from growing rapidly due to changes in the functioning and integrity of cellular and subcellular structures. Sterilized room Transducer Power Transformer High frequency agitator Power amplifier Matching impedance Feedback Figure 1. The novel ultrasonic generator designed and manufactured in our laboratory. This equipment can generate power ultrasound characterized by high requency (1.7 MHz) and low intensity (0.5-0.6 W cm - 2 ). Figure 3. Typical cavitation noise spectrum under ultrasonic irradiation at 1.7MHz Figure 2.Changes in electric con- ductivity with increase sonica-tion duration at the frequency of 1.7MHz.. Fig 4a. Control Fig 5a. Control Fig 4b.After 5 min ultrasonic irradiation Fig 5b.After 5 min ultrasonic irradiation Figure 4. Differential inter- ference microscopy of cells, showing details of the cell surface. The bumps and holes may result from collapse of gas- vesicles inside the cells. Figure 5. Confocal laser scanning microscopy of cells. The excited laser beam at 488 nm is an appropriate emission filter for chlorophyll. gas-vacuolate cyanobacterium vacuoles negative cyanobacterium Figure 6. Effect of 1.7 MHz ultrasonic irradiation on lipid peroxi- dation and additions of hydrogen peroxide. The relative content of MDA remarkably increased after ultrasonic irradiation, indicating that 1.7 MHz ultrasound did induce a comparable lipid peroxidation. Figure 7. Alternation of plasma membrane after ultrasonication in gas- vacuolate cyanobaterium ( Microcystis. aeruginosa) and vacuoles negative one (Synechococcus PCC. 7942). Large quantities of electrolyte seepages demonstrated terrible permeability of the membrane and its faultiness. Figure 8. Variation of chlorophyll a concentration in continuous culture. The contents of chlorophyll a of the control and the ultrasonic treated sample were evaluated on per gram dry weight of cells. Figure 9. Effect of ultrasonic irradiation on growth of gas-vacuolate cyanobacterium and vacuolate negative one. It was proposed that the cavitation occurs when the gas vesicles are acted upon by a sufficiently intense ultrasound beam of 1.7MHz. (a)Gas-vacuolate cyanobacterium (b) vacuolate nagetive one Figure 10. Effects of 1.7MHz ultrasonic irradiation on growth of Spirulina (Arthrospira) trichomes grown with various exposure durations. ○ Control, ∆ ultrasonic exposure for 1 minute,  for 3 minutes, ● for 5 minutes, ▲ for 7 minutes, ◆ for 9 minutes. Five minutes of ultrasonic irradiation resulted an effective inhibition. Figure 11. Effects of 1.7MHz ultrasonic treatment on Spirulina (Arthrospira) trichomes grown at the same level of energy input, but with diverse modes. ○ Control, ▲ ultrasonic exposure for 1 minute everyday,  for 2 minutes every other day, ● for 4 minutes every three days, ∆ for 6 minutes every five days,  for 12 minutes every eleven days. It is suggested that distributed ultrasonic irradiation is a practical method to prevent cyanobacterial cells from fast growth. Fig 10. Fig 11. Fig 6. Fig 7. Fig 8. gas-vacuolate cyanobacterium vacuoles negative cyanobacterium *Author for correspondence: (e-mail) qingyu@tsinghua.edu.cn ; (Tel) 010-62781825qingyu@tsinghua.edu.cn