Establishment of a new strategy against Microcystis bloom using newly isolated lytic and toxin-degrading bacteria

Unwanted, rapid increases in the algal populations of water systems cause harmful algal blooms, which have recently become a major environmental problem. The cyanobacterium Microcystis aeruginosa is the most prevalent bloom species and is responsible for the majority of blooms in freshwater environments. In this study, we attempted to develop an eco-friendly method to suppress M. aeruginosa bloom based on a biological control using bacteria newly isolated from the soil. In a screen for bacteria with strong lethal activity toward Microcystis, we isolated Bacillus sp. T4 and characterised its algicidal activity. Microcystis aeruginosa cells were killed via indirect attack by compound(s) secreted by T4 bacteria. ELISA revealed a dramatic increase in extracellular microcystins in M. aeruginosa cultures upon treatment with T4. Therefore, we screened for bacteria that could degrade these toxins, and three new isolates (R12, S42 and S65) were identified. Simultaneous application of both T4 as a lytic agent and R12 or S42 as toxin-degrading bacteria could eliminate both Microcystis cells and its problematic toxin. Our eco-friendly approach, based on the application of newly isolated bacteria, provides a novel method to control harmful algal blooms.