Microplastic characteristics differentially influence cyanobacterial harmful algal bloom microbial community membership, growth, and toxin production

Abstract Terrestrial runoffs contribute to cyanobacterial harmful algal blooms (cHABs) by providing nutrients and other pollutants that may facilitate cyanobacterial growth. Microplastics (MPs) are being detected at increasing concentrations in various aquatic systems worldwide, including freshwater, yet the MP effects on cHAB formation, toxin production, and transport are largely unknown. We used the statistical design of experiments to elucidate microbe–plastic interactions with freshwater algal bloom communities obtained from a HAB event in the Great Lakes. These experiments measured the impact of differing sizes, concentrations, and UV aging times of polyethylene, polypropylene, and cellulose fibers on the chlorophyll-a content of Trichormus (previously Anabaena variabilis) and Microcystis aeruginosa and microcystin-LR content in M. aeruginosa. Additionally, we conducted metagenomic sequencing on the total community and 16S rRNA microbial community sequencing on members of the total community bound to plastics after 4 weeks of culturing. The results indicate that M. aeruginosa growth rate was inhibited in the presence of polymers, while production of microcystin-LR generally increased in the presence of MPs. Changes to growth of T. variabilis varied with polymer type, size, and UV aging time. These results suggest that specific MP characteristics, not just their presence, may influence the toxicity, growth, and dispersal of cHABs across aquatic systems.