A photocatalytic Anammox@LC-COF biohybrid overcomes oxidative stress defense for resilient nitrogen removal.

Anaerobic ammonium oxidation (anammox) is central to low-carbon nitrogen removal, but its engineering application remains vulnerable to environmentally induced oxidative stress, whereby excessive reactive oxygen species (ROS) accumulation damages functional proteins and disrupts proteostasis. Here, we developed a low-crystallinity covalent organic framework-coupled anammox photocatalytic biohybrid, Anammox@LC-COF, to enhance oxidative stress defense and proteostasis through renewable photogenerated electron input. Results showed that Anammox@LC-COF exhibited broad tolerance to various engineering disturbances, including dissolved oxygen, low temperatures, pH fluctuations, and nitrite shocks. During 95 days of prolonged oxidative stress, Anammox@LC-COF sustained a robust total nitrogen removal efficiency of approximately 85%, whereas conventional anammox declined to 50.10%. It also increased the live-cell fraction, electron transport system activity, and specific anammox activity by 1.93-fold, 4.52-fold, and 3.28-fold, respectively. Mechanistic analysis indicated that LC-COF-derived photogenerated electrons established a coordinated antioxidative mechanism coupling front-end ROS interception with back-end proteostasis restoration. Specifically, photogenerated electrons activated a latent superoxide reductase-bacterioferritin-mediated ROS-scavenging pathway in anammox bacteria. Together with the traditional SOD-CAT antioxidant system, this dual pathway resulted in a 73.14% lower intracellular ROS level and curtailed oxidative damage at its source. In addition, photogenerated electrons enhanced the ferredoxin/thioredoxin reductive network by 1.97-fold, promoting chaperone-assisted refolding and quality control-mediated damaged protein clearance. This supported the recovery of core anammox metabolism under oxidative stress, with predicted HDH- and HZS-encoding gene abundances increasing by 4.26- and 1.43-fold, respectively. Overall, this photocatalytic biohybrid provides a broadly applicable solution to anammox environmental sensitivity, advancing its deployment in sustainable wastewater treatment.