NorV has been known to be an anaerobic nitric oxide reductase associated with nitric oxide (NO) detoxification. Recently, we showed that the norV gene of Aeromonas hydrophila was highly upregulated after co-culturing with Tetrahymena thermophila. Here, we demonstrated that the transcription and expression levels of norV were upregulated in a dose-dependent manner after exposure to NO under aerobic and anaerobic conditions. To investigate the roles of norV in resisting predatory protists and virulence of A. hydrophila, we constructed the norV gene-deletion mutant (ΔnorV). Compared to the wild type, the ΔnorV mutant showed no significant difference in growth at various NO concentrations under aerobic conditions but significantly stronger NO-mediated growth inhibition under anaerobic conditions. The deletion of norV exhibited markedly decreased cytotoxicity, hemolytic and protease activities under aerobic and anaerobic conditions. Also, the hemolysin co-regulated protein (Hcp) in the ΔnorV mutant showed increased secretion under aerobic conditions but decreased secretion under anaerobic conditions as compared to the wild-type. Moreover, the inactivation of norV led to reduced resistance to predation by T. thermophila, decreased survival within macrophages and highly attenuated virulence in zebrafish. Our data indicate a diverse role for norV in the expression of A. hydrophila virulence-associated traits that is not completely dependent on its function as a nitric oxide reductase. This study provides insights into an unexplored area of NorV, which will contribute to our understanding of bacterial pathogenesis and the development of new control strategies for A. hydrophila infection.

中文翻译：

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一氧化氮还原酶NorV对好氧和厌氧条件下嗜水气单胞菌毒力相关性状的不同影响。

已知NorV是与一氧化氮（NO）排毒相关的厌氧型一氧化氮还原酶。最近，我们显示嗜水气单胞菌的norV基因与嗜热四膜膜虫共培养后高度上调。在这里，我们证明了在有氧和厌氧条件下暴露于NO后，norV的转录和表达水平以剂量依赖的方式上调。为了研究norV在抵抗嗜水气单胞菌的掠食性原生生物和毒力中的作用，我们构建了norV基因缺失突变体（ΔnorV）。与野生型相比，ΔnorV突变体在好氧条件下各种NO浓度下的生长均无明显差异，但在厌氧条件下NO介导的生长抑制作用明显增强。在有氧和厌氧条件下，norV的缺失表现出明显的细胞毒性，溶血和蛋白酶活性降低。此外，与野生型相比，ΔnorV突变体中的溶血素共调节蛋白（Hcp）在有氧条件下显示分泌增加，而在无氧条件下显示分泌减少。此外，norV的失活导致嗜热链球菌对捕食者的抵抗力降低，巨噬细胞内的存活率降低以及斑马鱼的毒力大大降低。我们的数据表明，norV在嗜水链球菌毒力相关性状的表达中起着不同的作用，而该性状并不完全依赖于其作为一氧化氮还原酶的功能。这项研究提供了对NorV尚未探索的领域的见解，