ZntR is a critical regulator for zinc homeostasis and involved in pathogenicity in <i>Riemerella anatipestifer</i>

Zinc (Zn²⁺) is essential for all bacteria, but excessive Zn²⁺ levels are toxic. Bacteria maintain zinc homeostasis through regulators, such as Zur, AdcR, and ZntR. <i>Riemerella anatipestifer</i> is a significant <i>Flavobacteriales</i> pathogen causing acute serositis in ducks and other birds. In this study, we identified a homolog of ZntR, a regulator for zinc homeostasis, and demonstrated its contribution to the pathogenicity of <i>R. anatipestifer</i>. Deletion of <i>zntR</i> makes the bacteria hypersensitive to excess Zn²⁺ but not to other metals like manganese (Mn²⁺), copper (Cu²⁺), cobalt (Co²⁺), and nickel (Ni²⁺). Deletion of <i>zntR</i> also leads to intracellular zinc accumulation but not of other metals. Additionally, compared to the wild type, the deletion of <i>zntR</i> increases resistance to oxidants hydrogen peroxide (H₂O₂) and sodium hypochlorite (NaOCl), respectively. The deletion of <i>zntR</i> causes significant changes in transcriptional and protein expression levels, revealing 35 genes with potential zinc metabolism functions. Among them, <i>zupT</i>, which is inhibited by ZntR, is required for zinc transport and resistance to oxidative stress. Finally, deletion of <i>zntR</i> leads to attenuation of colonization in ducklings. In summary, ZntR is a crucial regulator for zinc homeostasis and contributes to the pathogenicity of <i>R. anatipestifer</i>.IMPORTANCEZinc homeostasis plays a critical role in the environmental adaptability of bacteria. <i>Riemerella anatipestifer</i> is a significant pathogen in poultry with the potential to encounter zinc-deficient or zinc-excess environment. The mechanism of zinc homeostasis in this bacterium remains largely unexplored. In this study, we showed that the transcriptional regulator ZntR of <i>R. anatipestifer</i> is critical for zinc homeostasis by altering the transcription and expression of a number of genes. Importantly, ZntR inhibits the transcription of zinc transporter ZupT and contributes to colonization in <i>R. anatipestifer</i>. The results are significant for understanding zinc homeostasis and the pathogenic mechanisms in <i>R. anatipestifer</i>.