Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, Jiangsu, China.
Key Lab of Food Quality and Safety of Jiangsu Province-State Key Laboratory Breeding Base, Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, Jiangsu, China.
Appl Microbiol Biotechnol. 2019 May;103(10):4203-4215. doi: 10.1007/s00253-019-09757-4. Epub 2019 Apr 10.
The TonB system functions in iron transport and has been identified in certain Gram-negative bacteria. Recently, we reported three TonB systems in the Aeromonas hydrophila Chinese epidemic strain NJ-35, but the functions of these systems have not been thoroughly elucidated to date. In this study, we investigated the role of these TonB systems in A. hydrophila iron utilization and virulence. We found that tonB1 and tonB2 were preferentially transcribed in iron-chelated conditions, where gene expression levels were approximately 8- and 68-fold higher compared with iron-rich conditions, respectively; tonB3 was consistently transcribed at a low level under iron-repleted and iron-depleted conditions. Only the TonB2 system was required to utilize iron-binding proteins. The tonB123 mutant showed increased susceptibility to erythromycin and roxithromycin. In addition, all three tonB genes were involved in A. hydrophila virulence in zebrafish, and various phenotypes associated with environmental survival were changed with varying degrees in each tonB mutant. TonB2 plays a relatively major role in adhesion, motility, and biofilm formation, while TonB3 is more involved in the anti-phagocytosis of A. hydrophila. In each observed phenotype, no significant difference was found between the single- and double-deletion mutants, whereas the triple-deletion mutant exhibited the most serious defects, indicating that all three TonB systems of A. hydrophila coordinately complement one another. In conclusion, this study elucidates the importance of TonB in iron acquisition and virulence of A. hydrophila, which lays the foundation for future studies regarding the survival mechanisms of this bacterium in iron-restricted environments.
TonB 系统在铁运输中起作用，并在某些革兰氏阴性菌中被发现。最近，我们报道了三种 TonB 系统在嗜水气单胞菌中国流行株 NJ-35 中，但这些系统的功能尚未得到彻底阐明。在这项研究中，我们研究了这些 TonB 系统在嗜水气单胞菌铁利用和毒力中的作用。我们发现 tonB1 和 tonB2 在铁螯合条件下优先转录，基因表达水平分别比富铁条件下高约 8 倍和 68 倍；tonB3 在铁充足和缺铁条件下始终以低水平转录。只有 TonB2 系统需要利用铁结合蛋白。tonB123 突变体对红霉素和罗红霉素的敏感性增加。此外，所有三种 tonB 基因都参与了嗜水气单胞菌在斑马鱼中的毒力，并且每种 tonB 突变体的环境生存相关各种表型都发生了不同程度的变化。TonB2 在粘附、运动和生物膜形成中起相对主要的作用，而 TonB3 更参与嗜水气单胞菌的抗吞噬作用。在观察到的每种表型中，单突变体和双突变体之间没有发现显著差异，而三突变体表现出最严重的缺陷，表明嗜水气单胞菌的三种 TonB 系统协同互补。总之，这项研究阐明了 TonB 在嗜水气单胞菌铁摄取和毒力中的重要性，为今后研究该菌在缺铁环境中的生存机制奠定了基础。
