The autotoxicity of dissolved organic matter from Microcystis may be a contributor to the decline of its bloom.

Microcystis blooms frequently occur in freshwaters worldwide, causing detrimental impacts on the ecosystems and human health. Studying the mechanisms behind the decline of Microcystis blooms can aid in mitigating their harmful effects. However, there is currently a dearth of research in this area. In this study, we examined the dissolved organic matter (DOM) collected during the growth of axenic Microcystis. Axenic Microcystis produces toxic DOM during its growth, which accumulate in the medium. Further, the DOM obtained from decline phase of Microcystis blooms exhibited a strong inhibitory effect on the growth of fresh Microcystis cultures. It is postulated that DOM may contribute to decline of Microcystis blooms. Meanwhile, potential autotoxic components in Microcystis DOM were analyzed by integrating column chromatography fractionation, identification and Microcystis growth inhibition assay. The results showed that the autotoxic components consisted mainly of small molecule hydrophobic base. Moreover, we evaluated the influence of key environmental factors such as nutrient and temperature on the autotoxic DOM in Microcystis cultures. Nutrient deficiency and low temperature may promote the accumulation of autotoxic substances. The study provided a new perspective on the decay process of cyanobacterial bloom, and offered new ideas for the development of natural algicidal agents.