Transcriptome deciphered the mechanisms of iron facilitating enzyme-mediated ciprofloxacin biodegradation and regulating antibiotic resistance gene dissemination through inducing genes expression

Abstract

Refractory chemically synthesized quinolones are frequently detected in aquatic environments, and their degradation via biological systems presents substantial challenges, which includes obstacles in undergoing biological transformation, residual toxicity, the enrichment and dissemination of antibiotic resistance genes (ARGs) induced by quinolones. Various forms of iron, including zero-valent iron (ZVI), Fe (II), and Fe (III), were employed to enhance the biodegradation of quinolones and associated environmental risks control in toxicity-tolerated hydrolysis acidification (HA) system in this research. Iron addition significantly improves ciprofloxacin (CIP) removal (22.8% to 41.28% increase) through improving activity of enzymes, especially for the identified dehydrogenases via meta-transcriptomic sequencing. Regarding the risks associated with ARGs and their dissemination, ZVI and Fe(Ⅱ) exhibit positive effects, while Fe(Ⅲ) has an inverse effect. The minimized residual CIP contributes to the reduction of reactive oxygen species (ROS) responsiveness and cellular membrane permeability, thereby decreasing the risks of ARGs dissemination in iron-added systems. However, the enrichment of Fe(Ⅲ) reduction bacteria in Fe(Ⅲ)-added HA systems was speculated to led to increased ARGs dissemination by generating additional ROS and causing cell damage during the Fe(Ⅲ) biological reduction process. Changes in relevant gene expression for ARG conjunction, ROS generation, cell membrane permeability, and DNA repair, as observed through qPCR and meta-transcriptomic sequencing, support these conclusions. The findings suggest that ZVI and Fe(Ⅱ) contribute to reducing risks associated with ARGs and their dissemination in the biological system, which could be prioritized. This research also contributes insights into efficient quinolone removal and environmental risk migrating simultaneously through iron-enhanced biodegradation processes.