Santos Mary Nia M, Cho Shu-Ting, Wu Chih-Feng, Chang Chun-Ju, Kuo Chih-Horng, Lai Erh-Min
Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan.
Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, National Chung Hsing University and Academia Sinica, Taipei, Taiwan.
Front Microbiol. 2020 Jan 14;10:3004. doi: 10.3389/fmicb.2019.03004. eCollection 2019.
Type VI secretion system (T6SS) is a contractile nanoweapon employed by many Proteobacteria to deliver effectors to kill or inhibit their competitors. One T6SS gene, , encodes a spike protein for effector translocation and is often present as multiple copies in bacterial genomes. Our phylogenomic analyses sampled 48 genomes across diverse Proteobacteria lineages and found ∼70% of them encode multiple VgrGs, yet only four genomes have nearly identical paralogs. Among these four, 1D1609 has the highest redundancy. Compared to model strain C58 which harbors two genes, 1D1609 encodes four genes (i.e., -) with each adjacent to different putative effector genes. Thus, 1D1609 was selected to investigate the functional redundancy and specificity of multiple genes and their associated effectors. Secretion assay of single and multiple deletion mutants demonstrated that these four s are functionally redundant in mediating T6SS secretion. By analyzing various mutants, we found that all except for the divergent could contribute to 1D1609's antibacterial activity. Further characterizations of putative effector-immunity gene pairs revealed that -associated gene 2 () encodes an AHH family nuclease and serves as the major antibacterial toxin. Interestingly, C58's VgrG2 shares 99% amino acid sequence identity with 1D1609's VgrGa, VgrGc and VgrGd. This high sequence similarity allows 1D1609 to use an exogenous VgrG delivered from C58 to kill another competing bacterium. Taken together, can use highly similar VgrGs, either produced endogenously or injected from its close relatives, for T6SS-mediated interbacterial competition.
VI型分泌系统（T6SS）是许多变形菌用来输送效应蛋白以杀死或抑制其竞争者的一种可收缩的纳米武器。一个T6SS基因，编码一种用于效应蛋白转运的刺突蛋白，并且在细菌基因组中通常以多个拷贝的形式存在。我们的系统基因组分析对不同变形菌谱系中的48个基因组进行了采样，发现其中约70%的基因组编码多个VgrG蛋白，但只有四个基因组具有几乎相同的旁系同源物。在这四个基因组中，1D1609的冗余度最高。与携带两个基因的模式菌株C58相比，1D1609编码四个基因（即 - ），每个基因都与不同的假定效应蛋白基因相邻。因此，选择1D1609来研究多个基因及其相关效应蛋白的功能冗余性和特异性。单缺失和多缺失突变体的分泌试验表明，这四个基因在介导T6SS分泌方面功能冗余。通过分析各种突变体，我们发现除了差异较大的外，所有基因都有助于1D1609的抗菌活性。对假定的效应蛋白 - 免疫基因对的进一步表征表明，与相关的基因2（）编码一种AHH家族核酸酶，并作为主要的抗菌毒素。有趣的是，C58的VgrG2与1D1609的VgrGa、VgrGc和VgrGd具有99%的氨基酸序列同一性。这种高度的序列相似性使得1D1609能够利用从C58传递来的外源性VgrG来杀死另一种竞争性细菌。综上所述，能够利用高度相似的VgrG蛋白，无论是内源性产生的还是从其近亲注入的，来进行T6SS介导的细菌间竞争。
