Tylosin Removal Under Pb²⁺ Stress Using Kurthia gibsonii TYL-A1: Redox Adaptation and Transcriptomic Insights

With the increasing prevalence of antibiotic-heavy metal co-contamination in agricultural wastewater, elucidating the antibiotic removal capacity of degrading bacteria under heavy metal stress, as well as their adaptive mechanisms, is of considerable theoretical significance and practical value. In this study, the highly efficient TYL-degrading strain TYL-A1 was selected as a model organism, and the effects of Pb²⁺ exposure on its TYL removal performance, oxidative stress response, cell surface characteristics, and transcriptional regulation were systematically investigated. The results showed that TYL removal remained above 85% after 72 h under a nominal Pb²⁺ concentration of 100 mg/L in the phosphate-containing MSM system. The phosphate may have reduced Pb²⁺ bioavailability. Nominal Pb²⁺ exposure increased the activities of superoxide dismutase (SOD) and catalase (CAT), accompanied by elevated levels of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as a decrease in adenosine triphosphate (ATP) content. This indicates that the strain experienced pronounced oxidative stress and altered energy metabolism. Meanwhile, cell membrane permeability increased. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses showed that the overall cellular morphology remained intact, whereas the membrane surface structure and related cellular components underwent adaptive changes. According to a transcriptomic analysis, the differentially expressed genes were mainly enriched in pathways associated with primary metabolism, transmembrane transport, ABC transporters, and two-component systems. In summary, strain TYL-A1 maintained high TYL removal performance under the tested nominal Pb²⁺ concentrations in the present phosphate-containing culture system, suggesting its potential applicability in the bioremediation of water bodies co-contaminated with antibiotics and heavy metals.