Targeted Inhibition of Bacterial Repair by Nitrite-Derived Reactive Nitrogen Species Improves UVC Disinfection Efficiency.

UVC irradiation is widely used for disinfection, yet its efficacy is sometimes compromised by bacterial photoreactivation and dark repair. This study demonstrates that pre-exposure to UVA irradiation in the presence of environmentally relevant nitrite (NO2-) significantly suppresses both repair pathways during subsequent UVC treatment. At 1.0 mg-N L-1 NO2- and 612 mJ cm-2 UVA, sequential (UVA-UVC)/NO2- treatment reduced photoreactivation and dark repair to less than 6% and 3%, respectively. This inhibition was consistent across four representative waterborne bacteria, including Gram-negative (E. coli and A. hydrophila) and Gram-positive (S. aureus and B. subtilis) strains, and remained effective in aquaculture tailwater and municipal secondary effluent (indigenous NO2- ≤ 0.3 mg-N L-1). Single-species dominant systems identified ONOO-/HOONO and NO2•, rather than HO• or NO•, as the primary mediators of repair suppression. Mechanistic investigations revealed that low-dose RNS did not cause nonspecific structural damage but instead selectively disrupted ATP biosynthesis by targeting key tricarboxylic acid cycle enzymes, including isocitrate dehydrogenase and citrate synthase. Resulting ATP depletion reduced transcription of recA, phr, and other repair-related genes, preventing activation of the bacterial repair machinery. This work provides a sustainable, low-dose, and highly targeted method to overcome bacterial repair and improve UVC disinfection efficiency.