Photosystem-Driven Resilience of Green Microalga Tetraselmis chuii toward Acute Nonylphenol Stress

Anthropogenic chemicals pose a threat to aquatic ecosystems by targeting the microalgal photosynthetic engines that drive primary production. Although the toxic effects of emerging contaminants such as nonylphenol (NP) are well-acknowledged, the molecular mechanisms enabling microalgal resilience remain largely unknown. Here, we integrate multiomics analyses with physiochemical assays to decipher the dynamic molecular blueprint of photosystem-driven resilience in the green microalga Tetraselmis chuii under NP stress. We demonstrated that microalgal resilience is not a passive defense mechanism but rather an active and energy-intensive restructuring of the photosynthetic apparatus. This strategy involves a strategic trade-off of a coordinated sacrifice of light-harvesting antennae, with a persistent low chlorophyll ( b / a ) ratio, to protect photosynthetic core complexes. This response is accompanied by a substantial metabolic shift from heme to chlorophyll biosynthesis, enhanced production of high-energy carriers (NADPH and ATP), and increased carbon fixation to support repair processes. Multiple interconnected photoprotective strategies are employed against reactive oxygen species, including chlorophyll breakdown, coordinated upregulation of carotenoid and α-tocopherol, and photosystem II subunit S (PsbS)-dependent nonphotochemical quenching. The understanding of microalgal resilience under chemical stress provides critical implications for assessing aquatic ecosystem health, guiding microalgae-based bioremediation, and informing global risk assessments of emerging contaminants.