Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
College of Animal Science and Technology, Jinling Institute of Technology, Nanjing, 211169, China.
Vet Res. 2019 Sep 23;50(1):67. doi: 10.1186/s13567-019-0683-6.
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.
NorV 是一种与一氧化氮 (NO) 解毒相关的厌氧型一氧化氮还原酶。最近，我们发现嗜水气单胞菌的 norV 基因在与嗜热四膜虫共培养后会高度上调。在这里，我们证明了 norV 的转录和表达水平在有氧和厌氧条件下受到 NO 暴露的影响呈剂量依赖性上调。为了研究 norV 在抵抗捕食性原生动物和嗜水气单胞菌毒力方面的作用，我们构建了 norV 基因缺失突变体（ΔnorV）。与野生型相比，ΔnorV 突变体在有氧条件下不同 NO 浓度下的生长没有显著差异，但在厌氧条件下，NO 介导的生长抑制作用明显增强。norV 的缺失导致有氧和厌氧条件下的细胞毒性、溶血和蛋白酶活性明显降低。此外，与野生型相比，ΔnorV 突变体中的溶血性细胞调控蛋白 (Hcp) 在有氧条件下的分泌增加，而在厌氧条件下的分泌减少。而且，norV 的失活导致对嗜热四膜虫的捕食抵抗力降低，在巨噬细胞内的存活率降低，以及在斑马鱼中的毒力显著降低。我们的数据表明 norV 在表达嗜水气单胞菌毒力相关特征方面具有多种作用，这并不完全依赖于其作为一氧化氮还原酶的功能。本研究为 NorV 的一个未探索领域提供了新的见解，这将有助于我们理解细菌发病机制，并为控制嗜水气单胞菌感染开发新的策略。
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