UV/sulfite-driven reductive bio-inactivation through collapse of cellular integrity and molecular functionality

Oxidative disinfection is widely used in aquaculture but often generates toxic by-products (DBPs) that limit its application. Advanced reduction processes (ARPs) provide a complementary strategy for controlling DBPs and possess potential to inactivate microorganisms by disrupting nucleic acids, proteins and other biomacromolecules, mediated by the reducing reactive species, including hydrated electrons (e_aq^-) and hydrogen atoms (•H). Here, we assessed the efficacy of UV-activated sulfite (UV/sulfite, a typical ARP) against four representative microorganisms from marine aquaculture. Within 5-40 min treatment, inactivation of the bacterium Escherichia coli, the fungus Fusarium oxysporum, the alga Heterosigma akashiwo and the ciliate Uronema marinum effectively achieved 4.70-log, 4.63-log, 3.45-log and 2.44-log, respectively. Density functional theory (DFT) calculations and degradation analyses of the model compounds demonstrated that the cell wall components, nucleic acids and amino acid residues were preferentially targeted by UV/sulfite treatment. Transcriptomic analyses indicated that UV/sulfite induced systemic cellular stress that disrupted ribosome biogenesis, DNA repair, protein homeostasis and energy metabolism in the microorganisms. In real marine aquaculture water, UV/sulfite treatment achieved over 6-log reductions of total bacteria within 30 min, effectively suppressed the pathogenic bacteria such as Vibrio and Salmonella, and maintained low levels of both organic and inorganic DBPs. This work provides a mechanistic insight into microbial inactivation by ARPs at the cellular and molecular levels, and demonstrates a practical, low-risk strategy to eliminate pathogenic microorganisms while minimizing DBPs formation in marine aquaculture water.