Colony formation of toxic Microcystis aeruginosa affected by microplastics-derived organic matter

Cyanobacterial blooms and microplastic (MP) pollution have become increasingly prominent global environmental issues. This study investigated the effects of polyethylene-derived organic matter (PE-DOM) and polylactic acid-derived organic matter (PLA-DOM) on the growth and physiological characteristics of Microcystis aeruginosa (M. aeruginosa). Fluorescence spectroscopy revealed that both PLA-DOM and PE-DOM contained tryptophan-like compounds that promoted the growth of M. aeruginosa, with PLA-DOM exhibiting higher concentrations of these compounds. Elemental analysis indicated that both MPs-DOM provided essential trace elements such as Mg, Na, Ca, and Zn, which are crucial for algal growth. Both MPs-DOM treatments increased cell biomass, chlorophyll-a content, polysaccharide and protein contents, and the activities of catalase (CAT) and superoxide dismutase (SOD), while also improving photosynthetic parameters. These results suggest that MPs-DOM foster M. aeruginosa growth by enhancing nutrient availability, photosynthetic efficiency, and stress tolerance. Overall, M. aeruginosa showed better growth at higher concentrations of DOM and better growth under exposure to PLA-DOM. Furthermore, MPs-DOM enhanced the expression of mcyB and mcyD, leading to the production and release of microcystin-LR (MC-LR), which promoted the formation of dominant M. aeruginosa populations. These findings provide new insights into the formation of cyanobacterial blooms and the ecological risks posed by MP pollution.