The dissemination of antibiotic resistance genes and heavy metal resistance genes along the sewage pipe under Cu and Zn stress

The long-term existence of heavy metals in sewage pipe was one of the selective pressures of resistance genes. This work explored the dissemination mechanisms of antibiotic resistance genes and heavy metal resistance genes under Cu and Zn stress and their dissemination differences at different locations along the pipe. It was found that at lower Cu and Zn concentrations, microorganisms secreted more extracellular polymeric substance for self-protection, with a 77.83% increase at 14 d. Moreover, the potential hosts of efflux pump genes were resistant to Cu and Zn. It could be inferred that the co-resistance and cross-resistance induced by heavy metals promote the horizontal gene transfer. When Cu and Zn concentrations were higher, the combined stress exceeded the impact of water flow, becoming the primary external environmental pressure. The differences of extracellular polymeric substance, protein and PS contents became smaller among the front, middle and posterior of pipe. While at the front, the microorganisms were more abundant, and the relative abundance of most resistance genes were higher. The study revealed the dissemination law of genes in sewage pipe under Cu and Zn stress, and laid theoretical foundations for further research on blocking the dissemination of genes.