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Toxic effects of polylactic acid microplastics on photosynthesis and motility of Microglena sp.
Summary
Polylactic acid microplastics — made from a supposedly biodegradable plastic — inhibited the growth, photosynthesis, and swimming ability of a marine microalgae species, with genes controlling flagella and photosynthesis both suppressed. This matters because microalgae form the base of marine food chains, and even 'eco-friendly' bioplastics can cause real ecological harm as they break down.
Mobility is critical for the survival of flagellated microalgae and plays a key role in maintaining marine ecosystem stability. To assess the environmental risks posed by polylactic acid microplastics (PLA-MPs), we investigated their effects on the photosynthesis and motility of Microglena sp. through indoor and outdoor mesocosm experiments at concentrations of 10, 25, 50, 75, 225, and 375 particles/mL. Results reveal that PLA-MPs inhibited the growth of Microglena sp. in a dose-dependent manner, with a maximum inhibition rate of 44.07% at 375 particles/mL. Additionally, PLA-MPs disrupted photosynthetic activity, chlorophyll biosynthesis, and induced oxidative stress. The swimming velocity and motility patterns of Microglena sp. were also significantly affected. Transcriptomic analysis demonstrated that down-regulation of flagella-related genes contributed to reduced motility, while suppressed photosynthetic gene expression corresponded to decreased photosynthetic efficiency. These findings enhanced our understanding of the adverse effects of PLA-MPs on microalgae and provide valuable insights for evaluating the ecological risks of PLA-MPs in marine ecosystem.