Nano-cyanocides for selective elimination of harmful cyanobacterial blooms in freshwater aquaculture

Harmful cyanobacterial blooms (HCBs) pose a major threat for the rapidly growing freshwater aquaculture sector. Aquaculture operations are predominantly based on green-water ponds, where naturally-occurring phytoplankton species ensure water oxygenation and nutrient recycling while providing natural food source for cultured fish. However, the combination of high levels of light, nutrients and elevated water temperatures promote the growth of HCBs over other phytoplankton species, particularly during the summer months. HCBs directly impact fish quality by the release of malodorous compounds that accumulate in the fish, giving them an unpleasant musty smell. Safety of human consumers and aquaculture workers is also affected due to the production of a diverse suite of cyanotoxins, particularly hepatotoxins such as microcystins and nodularins. Fish grown in HCB-affected water were shown to contain cyanotoxins at levels exceeding WHO recommendations. Though available algaecides are generally effective at controlling HCBs, their non-specific activity leads to temporary loss of the beneficial phytoplankton community, as well as harming non-target organisms. Here we report the efficacy of chlorinated nanoparticles (Cl NPs) in selectively eliminating cyanobacteria, including the universal bloom-forming species Microcystis aeruginosa, while having minimal effect on eukaryotic algae. Cl NPs action is distinct from that of other chlorinating agents, possibly due to the targeted release of free chlorine upon contact with the cell surface. We present result from a simple microfluidic platform enabling the use of live-imaging microscopy to directly demonstrate the effect of Cl NPs on both laboratory cultures and natural populations of cyanobacteria at single-cell resolutions. The combined results demonstrate a potential for future Cl NPs-based selective cyanocides for the elimination of HCBs with minimal effect on other members of the aquatic community.