Section Molecular Microbiology, Department of Biology, Faculty of Science and Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, the Netherlands.
FEMS Microbiol Lett. 2022 Jul 1;369(1). doi: 10.1093/femsle/fnac047.
Outer-membrane vesicles (OMVs) are promising tools in the development of novel vaccines against the respiratory pathogens Bordetella pertussis and Bordetella bronchiseptica. Unfortunately, vesiculation by bordetellae is too low for cost-effective vaccine production. In other bacteria, iron limitation or inactivation of the fur gene has been shown to increase OMV production, presumably by downregulation of the mla genes, which encode machinery for maintenance of lipid asymmetry in the outer membrane. Here, we followed a similar approach in bordetellae. Whereas a fur mutant was readily obtained in B. bronchiseptica, a B. pertussis fur mutant could only be obtained in iron-deplete conditions, indicating that a fur mutation is conditionally lethal in this bacterium. The fur mutants displayed a growth defect in iron-replete media, presumably because constitutive expression of iron-uptake systems resulted in iron intoxication. Accordingly, expression of the Escherichia coli ferritin FtnA to sequester intracellularly accumulated iron rescued the growth of the mutants in these media. The fur mutations led to the constitutive expression of novel vaccine candidates, such as the TonB-dependent receptors FauA for the siderophore alcaligin and BhuR for heme. However, neither inactivation of fur nor growth under iron limitation improved vesiculation, presumably because the expression of the mla genes appeared unaffected.
外膜囊泡 (OMVs) 是开发针对呼吸道病原体百日咳博德特氏菌和支气管败血波氏杆菌新型疫苗的有前途的工具。不幸的是，博德特氏菌的囊泡化效率太低，无法实现具有成本效益的疫苗生产。在其他细菌中，铁限制或 fur 基因失活已被证明会增加 OMV 的产生，这可能是通过下调 mla 基因来实现的，mla 基因编码维持外膜脂质不对称性的机制。在这里，我们在博德特氏菌中采用了类似的方法。虽然很容易在支气管败血波氏杆菌中获得 fur 突变体，但只能在缺铁条件下获得百日咳博德特氏菌的 fur 突变体，这表明 fur 突变在该细菌中是条件致死的。fur 突变体在富含铁的培养基中表现出生长缺陷，这可能是因为铁摄取系统的组成型表达导致铁中毒。因此，表达大肠杆菌铁蛋白 FtnA 将细胞内积累的铁隔离，挽救了这些培养基中突变体的生长。fur 突变导致新型疫苗候选物（例如，铁载体 alcaligin 的 TonB 依赖性受体 FauA 和血红素的 BhuR）的组成型表达。然而，fur 的失活或铁限制下的生长都没有改善囊泡化，这可能是因为 mla 基因的表达似乎没有受到影响。
