Genome-Wide Molecular\nAdaptation in Algal Primary\nProductivity Induced by Prolonged Exposure to Environmentally Realistic\nConcentration of Nanoplastics

Little\ninformation is known about the long-term effects\nof nanoplastics\n(NPs) in aquatic environments, especially under environmental-related\nscenarios. Herein, three differently charged NPs (nPS, nPS-NH<sub>2</sub>, and nPS-COOH) were exposed at an environmentally realistic\nconcentration (10 μg/L) for 100 days to explore the variation\nof primary productivity (i.e., algae) in aquatic ecosystems. Our results\ndemonstrated that the algae adapted to all three types of NPs by enhancing\nthe algal number (by 10.34–16.52%), chlorophyll a (by 11.28–17.65%),\nand carbon-fixing enzyme activity (by 49.19–68.33%), which\nwere further confirmed by the exposure results from natural water\nculturing experiments. Based on the algal chloroplast number and biovolume\nat the individual level, only nPS caused algal differentiation into\ntwo heterogeneous subpopulations (54.92 vs 45.08%), while nPS-NH<sub>2</sub> and nPS-COOH did not cause the differentiation of the algal\npopulation. Moreover, the molecular adaptation mechanisms of algae\nto NPs were unraveled by integrating epigenomics and transcriptomics.\nMean methylation rates of algae on exposure to nPS, nPS-NH<sub>2</sub>, and nPS-COOH were significantly elevated. In addition, the direction\nof gene expression regulation via differentially methylated regions\nassociated with genes when exposed to nPS-COOH was distinct from those\nof nPS and nPS-NH<sub>2</sub>. Our results highlight the importance\nof assessing the long-term ecotoxicity of NPs and provide useful information\nfor understanding the effect of NPs on aquatic ecosystems.