Dept. of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, United States of America.
PLoS Pathog. 2023 Aug 3;19(8):e1011537. doi: 10.1371/journal.ppat.1011537. eCollection 2023 Aug.
The bacterial flagellum is a rotary motor organelle and important virulence factor that propels motile pathogenic bacteria, such as Salmonella enterica, through their surroundings. Bacteriophages, or phages, are viruses that solely infect bacteria. As such, phages have myriad applications in the healthcare field, including phage therapy against antibiotic-resistant bacterial pathogens. Bacteriophage χ (Chi) is a flagellum-dependent (flagellotropic) bacteriophage, which begins its infection cycle by attaching its long tail fiber to the S. enterica flagellar filament as its primary receptor. The interactions between phage and flagellum are poorly understood, as are the reasons that χ only kills certain Salmonella serotypes while others entirely evade phage infection. In this study, we used molecular cloning, targeted mutagenesis, heterologous flagellin expression, and phage-host interaction assays to determine which domains within the flagellar filament protein flagellin mediate this complex interaction. We identified the antigenic N- and C-terminal D2 domains as essential for phage χ binding, with the hypervariable central D3 domain playing a less crucial role. Here, we report that the primary structure of the Salmonella flagellin D2 domains is the major determinant of χ adhesion. The phage susceptibility of a strain is directly tied to these domains. We additionally uncovered important information about flagellar function. The central and most variable domain, D3, is not required for motility in S. Typhimurium 14028s, as it can be deleted or its sequence composition can be significantly altered with minimal impacts on motility. Further knowledge about the complex interactions between flagellotropic phage χ and its primary bacterial receptor may allow genetic engineering of its host range for use as targeted antimicrobial therapy against motile pathogens of the χ-host genera Salmonella, Escherichia, or Serratia.
细菌鞭毛是一种旋转的马达器官，也是推动运动性病原体细菌（如沙门氏菌）在其周围移动的重要毒力因子。噬菌体，即 phage，是专门感染细菌的病毒。因此，噬菌体在医疗保健领域有多种应用，包括针对抗生素耐药性细菌病原体的噬菌体治疗。噬菌体 χ（Chi）是一种依赖于鞭毛的（鞭毛依赖性）噬菌体，它通过将其长尾纤维附着在沙门氏菌鞭毛丝上作为其主要受体开始其感染周期。噬菌体和鞭毛之间的相互作用知之甚少，以及 χ 仅杀死某些沙门氏菌血清型而其他血清型完全逃避噬菌体感染的原因也知之甚少。在这项研究中，我们使用分子克隆、靶向诱变、异源鞭毛蛋白表达和噬菌体-宿主相互作用测定来确定鞭毛丝蛋白鞭毛蛋白中哪些结构域介导这种复杂的相互作用。我们确定了抗原性 N 和 C 末端 D2 结构域对于噬菌体 χ 结合是必不可少的，而高度可变的中央 D3 结构域则起着不太关键的作用。在这里，我们报告沙门氏菌鞭毛蛋白 D2 结构域的一级结构是 χ 粘附的主要决定因素。菌株的噬菌体易感性直接与其相关。我们还发现了有关鞭毛功能的重要信息。中央和最可变的结构域 D3 对于鼠伤寒沙门氏菌 14028s 的运动不是必需的，因为它可以被删除，或者其序列组成可以被显著改变，而对运动的影响最小。进一步了解嗜旋毛虫 χ 与其主要细菌受体之间的复杂相互作用可能允许对其宿主范围进行基因工程改造，以用作针对 χ-宿主属沙门氏菌、大肠杆菌或沙雷氏菌等运动性病原体的靶向抗菌治疗。
