Chemical Proteomics Revealed Global Occurrence of a Phytoplankton Lyase Capable of Reconverting the Progestogens

Endocrine-disrupting chemicals (EDCs), such as progestogens, are generally recognized as environmental pollutants of global concern due to their pervasive and adverse effects on aquatic ecosystems and human health. Despite extensive research on their transformation by animals and bacteria (e.g., Denitratisoma sp.), the interactions between phytoplankton and progestogens remain poorly understood. In this study, we reveal a universal biotransformation of norethindrone acetate (NEA), a representative progestogen, across 18 phylogenetically diverse freshwater and marine phytoplankton species. All species demonstrated the ability to remove NEA from culture media (16.4–99.31% removal within 24 hours), primarily through enzymatic biodegradation. Notably, Chlamydomonas reinhardtii achieved complete NEA removal and further metabolized its main product, norethindrone (NET), a more potent neurosteroid, highlighting its biocatalytic efficiency. Further analysis using click chemistry-based chemical proteomics, combined with protein heterologous expression and purification, identified adenylosuccinate lyase has a binding affinity (KD) of 4.27 µM for NEA, acting as the key enzyme responsible for the deacetylation of NEA into NET in C. reinhardtii. This identified enzymatic role in phytoplankton is distinct from the β-elimination of fumarate seen in animal counterparts. Using metagenome and metatranscriptome database, we uncovered the global distribution and transcription of genes encoding this lyase across various eukaryotic phyla. Thus, the reconversion of NEA into NET by phytoplankton occurs in diverse Earth environments, which may exacerbate the risks of progestogens such as NEA to ecosystem health and human safety.