Light-driven community assembly and functional performance of aeration-free filamentous algae-partial nitrification/anammox granule.

The algae-partial nitrification/anammox (A-PNA) process offers significant advantages for carbon-neutral wastewater nitrogen removal. This study successfully established a zero-aeration filamentous algal-PNA (FA-PNA) granular system by incorporating Pantanalinema sp. under stepwise increasing light intensities (0, 15, 60 and 90 μmol·m⁻²·s⁻¹). Increasing light intensity promoted the enrichment of extracellular polymeric substances and filamentous algae, facilitating granular growth and achieving a nitrogen removal rate of 85 mg N·(L·d)⁻¹. Quorum-sensing signaling molecules concentration increased significantly with light intensity, particularly C6-HSL (p < 0.05). Symbiotic network and transcriptomic analyses identified Pantanalinema sp. served as a central interactive hub. It formed potential cross-feeding network with the microorganisms (Nitrosomonas europaea, Candidatus Brocadia sapporoensis, and Denitratisoma sp.) based on B vitamins (vitamin B1, vitamin B2, biotin, folate, and cobalamin) and molybdenum cofactor (MOCO). Under elevated light, these microorganisms upregulated the transcriptional expression levels of key genes involved in B vitamins and MOCO synthesis, signaling molecule production, and reactive oxygen species scavenging, forming an integrated network. This synergistic "stress protection-signaling-metabolite exchange" network effectively alleviated light-induced metabolic suppression. Additionally, Candidatus Brocadia sapporoensis exhibited superior light adaptation potential compared to Candidatus Kuenenia stuttgartiensis_A and Candidatus Jettenia sp., identifying its suitability for FA-PNA systems. Overall, FA-PNA system provides a promising route for low-energy, carbon-negative nitrogen removal in wastewater treatment.