Higher sensitivity of MC-producing Microcystis to two algaecides compared to co-cultured non-MC-producers

Targeting and selectivity are essential for assessing the effectiveness of ecofriendly algaecides in controlling toxic cyanobacterial blooms. The dose- and time-dependent effects of hydrogen peroxide (H 2 O 2 ), pyrogallol and their sustained-release microspheres (HRM, PRM) on proportion of MC-producing cell numbers and genotypes of the co-existing MC- and non-MC-producing Microcystis , as well as microcystins (MCs) concentrations were investigated in the present study. Two MC-producing and two non-MC-producing Microcystis strains were used in mono- and co-culture test systems. The findings revealed that the MC-producing Microcystis strains were more sensitive to both forms of H 2 O 2 and pyrogallol in comparison with the non-MC-producing strains. Inhibition of all Microcystis strains by H 2 O 2 and pyrogallol was found to be dose- and time-dependent, with H 2 O 2 exhibiting stronger effects. Additionally, both pure and granular forms of H 2 O 2 and pyrogallol reduced the relative abundance of MC-producing genotypes in co-culture conditions, along with total MC concentrations. The HRM and PRM demonstrated more potent and prolonged effects than their pure forms, indicating they are optimal for targeted reduction of Microcystis bloom toxicity. The release rate of MCs into the extracellular environment of Microcystis may exceed their degradation rate during H 2 O 2 and pyrogallol treatments. It resulted in elevated extracellular MC levels after treatment. Therefore, ongoing monitoring of environmental MCs is necessary following the inhibition of Microcystis population growth by algaecides.