Unveiling the molecular mechanisms of size-dependent effect of polystyrene micro/nano-plastics on Chlamydomonas reinhardtii through proteomic profiling

Microplastics have become a prevalent environmental pollutant due to widespread release and production. Algae, as primary producers, play a crucial role in maintaining the ecological balance of freshwater environments. Despite reports on the inhibition of microalgae by microplastics, the size-dependent effects on microalgae and associated molecular mechanism remain poorly understood. This study investigates the impacts of three polystyrene micro/nano-plastics (PS-MNPs) with different sizes (100 nm, 350 nm, and 6 μm) and concentrations (25-200 mg/L) on Chlamydomonas reinhardtii (C. reinhardtii) throughout its growth period. Results reveal size- and concentration-dependent growth inhibition and induction of oxidative stress by PS-MNPs, with microalgae exhibiting increased vulnerability to smaller-sized and higher-concentration PS-MNPs. Proteomics analysis elucidates the size-dependent suppression of proteins involved in the photosynthesis process by PS-MNPs. Photosynthetic activity assays demonstrate that smaller PS-MNPs more significantly reduce chlorophyll content and the maximal photochemical efficiency of photosystem II. Finally, electron microscope and Western blot assays collectively confirm the size effect of PS-MNPs on microalgae growth is attributable to suppressed protein expression rather than shading effects. This study contributes to advancing our understanding of the intricate interactions between micro/nano-plastics and algae at the molecular level, emphasizing the efficacy of proteomics in dissecting the mechanistic aspects of microplastics-induced biological effects on environmental indicator organisms.