Comparison of the impacts of zinc ions and zinc nanoparticles on nitrifying microbial community

To understand the effects of metal ions and nanoparticles (NPs) on nitrifying bacterial communities, this study investigates the impacts of zinc (Zn) NPs, zinc oxide (ZnO) NPs and Zn ions on the nitrifying bacterial communities. Under low Zn concentration (0.1 mg L−1), the nitrification rate was promoted by Zn ions and inhibited by the two NPs, indicating that the toxicity of NPs was caused by the NPs themselves instead of the released Zn ions. Further analysis showed that both Zn NPs and ZnO NPs could result in substantial reactive oxygen species (ROS) production in the nitrifying bacteria community. The inhibition was strongly correlated with amoA gene expression, but not with the expression of hao and nxrA genes. These results indicated that the main difference of the Zn ions and Zn NPs on nitrifying bacterial community could be due to the different impacts on the ROS production and amoA gene expression. Collectively, the findings in this study advanced understanding of the different effects of Zn NPs, ZnO NPs and Zn ions on nitrifying bacteria.