Photocatalysis-fueled algae-bacteria mutualism enables P450 enzyme-induced nitrite-free anammox for sustainable nitrogen removal.

Anaerobic ammonium oxidation (anammox) relies on scarce nitrite in wastewater to produce hydroxylamine, a key substrate for anammox nitrogen removal, severely limiting its sustainable implementation. This study pioneers a photocatalysis-driven algae-bacteria mutualistic platform for activating a microalgal P450 enzyme-induced nitrite-independent anammox pathway. This platform integrates two functional blocks: photocatalysis-induced P450 activation circuit, and P450-mediated algal-anammox nitrogen removal module. First, photocatalysis rewired microalgal carbon flux to foster cooperation with heterotrophic ACID1, enabling ACID1-derived salicylic acid to feedback-regulate the biosynthesis of key P450 cofactors-iron-porphyrin and Fe-S clusters. Meanwhile, photogenerated electrons boosted NADPH (FC=2.33), directly fueling P450 activation. In this way, microalgal P450 enzymes were robustly activated to unprecedented levels, emerging as the most abundant protein family in CYAN1. Second, P450-catalyzed monooxygenation of ammonia to hydroxylamine bypassed nitrite, enabling a previously inaccessible microalgae-anammox synergistic nitrogen removal mode, achieving an ultra-high nitrogen removal efficiency of 99 % without nitrite and with negligible greenhouse gas emissions. This strategy offers new insights into algal-bacterial cooperation and opens avenues for multi-channel solar-to-biochemical energy conversion in photocatalyst-microbe biohybrids for sustainable wastewater treatment.