Marine Colloids Promote the Adaptation of Diatoms to Nitrate Contamination by Directional Electron Transfer

Nitrate contamination from human activities (e.g., domestic pollution, livestock breeding, and fertilizer application) threatens marine ecosystems and net primary productivity. As the main component of primary productivity, diatoms can adapt to high nitrate environments, but the mechanism is unclear. We found that electron transfer from marine colloids to diatoms enhances nitrogen uptake and assimilation under visible-light irradiation, providing a new pathway for nitrogen adaptation. Under irradiation, marine colloids exhibit semiconductor properties (e.g., the separation of electron-hole pairs) and can trigger the generation of free electrons and singlet oxygen. They also exhibit electron acceptor and donor properties, with the former being stronger than the latter, reacting with polysaccharides in extracellular polymeric substances (EPSs) under high nitrogen stress, enhancing the elasticity and permeability of cells, and promoting nitrogen assimilation and electron transfer to marine diatom EPSs. Electron transfer promotes extracellular-to-intracellular nitrate transport by upregulating membrane nitrate transporters and nitrate reductase. The upregulation of anion transport genes and unsaturated fatty acids contributes to nitrogen assimilation. We estimate that colloids may increase the nitrate uptake efficiency of marine diatoms by 10.5-82.2%. These findings reveal a mechanism by which diatoms adapt to nitrate contamination and indicate a low-cost strategy to control marine pollution.