Multi-omics reveal an interfacial aromatic molecular bridge supporting photoelectron uptake and nitrogen removal in...

Microbe-semiconductor biohybrids can overcome the stoichiometric limitation of anaerobic ammonium oxidation (anammox) by supplying photogenerated electrons, yet the key interfacial electron uptake mechanisms of anammox bacteria remain elusive. Here, an illuminated anammox-CdS biohybrid was constructed and exhibited a high nitrate reduction rate of 1.35 ± 0.44 mg N/(g VSS·h), which was 10.4-fold higher than that of the dark anammox biomass control. After 72 h reaction, the total nitrogen removal reached 81.9% in the anammox-CdS biohybrid, while it was only 10.1% in the dark anammox biomass control; isotope tracing analysis proved anammox pathway as the dominant nitrogen removal pathway. A 43.4% increase in the areal capacitance indicated the enhanced charge-storage and electron-transfer capacity in anammox-CdS biohybrid, consistent with its improved nitrogen removal capacity. Metabolomic analysis further showed increased abundances of phenyl, phenolic, indole and flavonoid aromatic metabolites in the anammox-CdS biohybrid, accompanied by a 32% increase in the aromatic fluorescence signal of extracellular polymeric substances. These results suggest the formation of a potential aromatic molecular bridge that may maintain a local pool of redox-active metabolites and facilitate electron exchange at the anammox bacteria-CdS interface. Metaproteomics further demonstrated that Candidatus Brocadia sp. maintained fundamental aromatic biosynthesis, whereas Alicycliphilus denitrificans and Stenotrophomonas sp. contributed to downstream aromatic transformation. This work reveals the previously overlooked role of extracellular aromatic metabolite enrichment in mediating interfacial electron transfer in the anammox-CdS biohybrid, and highlights that engineering the interfacial metabolite environment could improve photoelectron utilization for sustainable and advanced nitrogen removal from wastewater.