The type VI secretion system (T6SS) is used by many bacteria to engage in social behavior and can affect the health of its host plant or animal. Because activities associated with T6SSs are often costly, T6SSs must be tightly regulated. However, our knowledge regarding how T6SS assembly and contraction are regulated remains limited. Using the plant pathogen Agrobacterium tumefaciens, we show that effectors are not just passengers but also impact on T6SS assembly. The A. tumefaciens strain C58 encodes one T6SS and two Tde DNase toxin effectors used as major weapons for interbacterial competition. Here, we demonstrate that loading of Tde effectors onto their cognate carriers, the VgrG spikes, is required for active T6SS secretion. The assembly of the TssBC contractile sheath occurs only in the presence of Tde effectors. The requirement of effector loading for efficient T6SS secretion was also validated in other A. tumefaciens strains. We propose that such a mechanism is used by bacteria as a strategy for efficacious T6SS firing and to ensure that effectors are loaded onto the T6SS prior to completing its assembly.

中文翻译：

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装载到 VgrG 载体上的效应器激活 VI 型分泌系统组装。


许多细菌利用 VI 型分泌系统 (T6SS) 来参与社会行为，并能影响宿主植物或动物的健康。由于与 T6SS 相关的活动通常成本高昂，因此必须严格监管 T6SS。然而，我们关于 T6SS 组装和收缩如何调控的知识仍然有限。使用植物病原体根癌农杆菌，我们证明效应子不仅是乘客，而且对 T6SS 组装也有影响。根癌农杆菌菌株 C58 编码一个 T6SS 和两个 Tde DNase 毒素效应子，用作细菌间竞争的主要武器。在这里，我们证明将 Tde 效应子加载到其同源载体 VgrG 尖峰上是主动 T6SS 分泌所必需的。 TssBC 收缩鞘的组装仅在 Tde 效应器存在的情况下发生。 T6SS 有效分泌所需的效应器负载要求也在其他根癌农杆菌菌株中得到了验证。我们建议细菌使用这种机制作为有效 T6SS 发射的策略，并确保效应器在完成组装之前加载到 T6SS 上。