Abstract：
Previous studies revealed that the type VI secretion system (T6SS) has an essential role in bacterial competition and virulence in many gram-negative bacteria. However, the role of T6SS in virulence in Pectobacterium atrosepticum remains controversial. We examined a closely related strain, PccS1, and discovered that its T6SS comprises a single-copy cluster of 17 core genes with a higher identity to homologs from P. atrosepticum. Through extensive phenotypic and functional analyses of over 220 derivatives of PccS1, we found that three of the five VgrGs could be classified into group I VgrGs. These VgrGs interacted with corresponding DUF4123 domain proteins, which were secreted outside of the membrane and were dependent on either the T6SS or type IV secretion system (T4SS). This interaction directly governed virulence and competition. Meanwhile, supernatant proteomic analyses with strains defective in the T6SS and/or T4SS confirmed that effectors, such as FhaB, were secreted redundantly to control the virulence and suppress host callose deposition in the course of infection. Notably, this redundant secretion mechanism between the T6SS and T4SS is believed to be the first of its kind in bacteria.
摘要：
先前的研究表明，VI型分泌系统（T6SS）在许多革兰氏阴性菌的细菌竞争和毒力中起着至关重要的作用。然而,T6SS在嗜酸性淋球菌毒力中的作用仍存在争议。我们检查了一个密切相关的菌株，PccS1，并发现其T6SS包含一个由17个核心基因组成的单拷贝簇，该基因与来自拟南芥的同源物具有较高的同一性。通过对PccS1的220多种衍生物进行广泛的表型和功能分析，我们发现五个VgrG中的三个可以归类为I组VgrG。这些VgrGs与相应的DUF4123结构域蛋白相互作用，它们在膜外分泌并依赖于T6SS或T4SS。这种相互作用直接控制毒力和竞争。同时,T6SS或/和T4SS中染色缺陷的上清液蛋白质组学分析证实，比如FhaB,冗余分泌以控制毒力并在感染过程中抑制宿主call的沉积。值得注意的是,T6SS和T4SS之间的这种冗余分泌机制被认为是细菌中的第一个。
