Ozone-Resistant\nBacteria, an Inconvenient Hazard in\nWater Reclamation: Resistance Mechanism, Propagating Capacity, and\nPotential Risks

Resistant bacteria have always been of research interest\nworldwide.\nIn the urban water system, the increased disinfectant usage gives\nmore chances for undesirable disinfection-resistant bacteria. As the\nstrongest oxidative disinfectant in large-scale water treatment, ozone\nmight select ozone-resistant bacteria (ORB), which, however, have\nrarely been reported and are inexplicit for their resistant mechanisms\nand physiological characteristics. In this study, six strains of ORB\nwere screened from a water reclamation plant in Beijing. Three of\nthem (O7, CR19, and O4) were more resistant to ozone than all previously\nreported ORB or even spores. The ozone consumption capacity of extracellular\npolymeric substances and cell walls was proved to be the main sources\nof bacterial ozone resistance, rather than intracellular antioxidant\nenzymes. The transcriptome results elucidated that strong ORB possessed\na combined antioxidant mechanism consisting of the enhanced transcription\nof protein synthesis, protein export, and polysaccharide export genes\n(<i>LptF</i>, <i>LptB</i>, <i>NodJ</i>, <i>LivK</i>, <i>LviG</i>, <i>MetQ</i>, <i>MetN</i>, and <i>GltU</i>). This study confirmed\nthe existence of ORB in urban water systems and brought doubts to\nthe idea of a traditional control strategy against chlorine-resistant\nbacteria. A salient “trade-off” effect between the ozone\nresistance and propagation ability indicated the weakness and potential\ncontrol approaches of ORB.