Novel treatment of Microcystis aeruginosa using chitosan-modified nanobubbles

In this study, we treated harmful Microcystis aeruginosa cyanobacteria using chitosan-modified nanobubbles. The chitosan-modified nanobubbles (255 +/- 19 nm) presented a positive zeta potential (15.36 +/- 1.17 mV) and generated significantly (p < 0.05) more hydroxyl radicals than the negatively charged nanobubbles (-20.68 +/- 1.11 mV). Therefore, the interaction between the positively charged chitosan-modified nanobubbles and negatively charged M. aeruginosa (-34.81 +/- 1.79 mV) was favored. The chitosan-modified nanobubble treatment (2.20 x 10(8) particles mL(-1)) inactivated 73.16% +/- 2.23% of M. aeruginosa (2.00 x 10(6) cells mL(-1)) for 24 h without causing significant cell lysis (<= 0.25%) and completely inhibited the acute toxicity of M. aeruginosa toward Daphnia magna. The inactivation was correlated (r(2) = 0.97) with the formation of reactive oxygen species (ROS) in M. aeruginosa. These findings indicated that the hydroxyl radicals generated by the chitosan-modified nanobubbles disrupted cell membrane integrity and enhanced oxidative stress (ROS formation), thereby inactivating M. aeruginosa. Moreover, the penetration of the chitosan-modified nanobubbles and cell alterations in M. aeruginosa were visually confirmed. Our results suggested that the chitosan-modified nanobubble treatment is an eco-friendly method for controlling harmful algae. However, further studies are required for expanding its practical applications.