Cyanobacteria mitigation using low power ultrasound for gas vesicle collapse

The ability of a low-power ultrasound system to alter the physiology of cyanobacteria cells in controlled field applications was evaluated. Serratia sp., a model bacteria, and cyanobacteria collected from a bloom containing Microcystis sp. and Aphanizomenon sp., were placed in sound transparent containers and exposed to ultrasound in field studies. No observed changes in Serratia sp. and cyanobacteria gas vesicles between unexposed controls and ultrasound exposed samples were found. Cell viability and phycocyanin concentration for both model bacteria and environmental samples were not significantly affected. At the highest acoustic pressure measured (3.5 kPa), 1 m from the transducer, the acoustic pressures were over 100× lower than gas vesicle critical collapse pressures. Moreover, the ultrasound frequencies emitted are significantly lower than gas vesicle resonance frequencies. Therefore, consistent with pressure and frequency measurements, we found no evidence that gas vesicle collapse is the mechanism of ultrasound as a cyanobacteria mitigation strategy.