Natural\nOrganic Matter Enhances Natural Transformation\nof Extracellular Antibiotic Resistance Genes in Sunlit Water

Antibiotic\nresistance genes (ARGs) as emerging environmental contaminants\nexacerbate the risk of spreading antibiotic resistance. Natural organic\nmatter (NOM) is ubiquitous in aquatic environments and plays a crucial\nrole in biogeochemical cycles. However, its impact on the dissemination\nof extracellular antibiotic resistance genes (eARGs) under sunlight\nexposure remains elusive. This study reveals that environmentally\nrelevant levels of NOM (0.1–20 mg/L) can significantly enhance\nthe natural transformation frequency of the model bacterium <i>Acinetobacter baylyi</i> ADP1 by up to 7.6-fold under simulated\nsunlight. Similarly, this enhancement was consistently observed in\nnatural water and wastewater systems. Further mechanism analysis revealed\nthat reactive oxygen species (ROS) generated by NOM under sunlight\nirradiation, primarily singlet oxygen and hydroxyl radicals, play\na crucial role in this process. These ROS induce intracellular oxidative\nstress and elevated cellular membrane permeability, thereby indirectly\nboosting ATP production and enhancing cell competence of extracellular\nDNA uptake and integration. Our findings highlight a previously underestimated\nrole of natural factors in the dissemination of eARGs within aquatic\necosystems and deepen our understanding of the complex interplay between\nNOM, sunlight, and microbes in environmental water bodies. This underscores\nthe importance of developing comprehensive strategies to mitigate\nthe spread of antibiotic resistance in aquatic environments.