Plant Microbe Interactions Laboratory, National Institute of Plant Genome Research, Aruna Asaf Ali Marg, India.
EMBO Rep. 2021 Jun 4;22(6):e51857. doi: 10.15252/embr.202051857. Epub 2021 Mar 30.
Bacteria utilize type VI secretion system (T6SS) to deliver antibacterial toxins to target co-habiting bacteria. Here, we report that Burkholderia gladioli strain NGJ1 deploys certain T6SS effectors (TseTBg), having both DNase and RNase activities to kill target bacteria. RNase activity is prominent on NGJ1 as well as other bacterial RNA while DNase activity is pertinent to only other bacteria. The associated immunity (TsiTBg) proteins harbor non-canonical helix-turn-helix motifs and demonstrate transcriptional repression activity, similar to the antitoxins of type II toxin-antitoxin (TA) systems. Genome analysis reveals that homologs of TseTBg are either encoded as TA or T6SS effectors in diverse bacteria. Our results indicate that a new ORF (encoding a hypothetical protein) has evolved as a result of operonic fusion of TA type TseTBg homolog with certain T6SS-related genes by the action of IS3 transposable elements. This has potentially led to the conversion of a TA into T6SS effector in Burkholderia. Our study exemplifies that bacteria can recruit toxins of TA systems as T6SS weapons to diversify its arsenal to dominate during inter-bacterial competitions.
细菌利用 VI 型分泌系统（T6SS）将抗菌毒素输送到目标共生细菌。在这里，我们报告称，甘蓝伯克霍尔德氏菌 NGJ1 菌株利用某些 T6SS 效应器（TseTBg），具有 DNA 酶和 RNA 酶活性来杀死目标细菌。NGJ1 以及其他细菌的 RNA 上具有明显的 RNA 酶活性，而 DNA 酶活性仅与其他细菌有关。相关的免疫（TsiTBg）蛋白含有非典型的螺旋-转角-螺旋基序，并表现出转录抑制活性，类似于 II 型毒素-抗毒素（TA）系统的抗毒素。基因组分析表明，TseTBg 的同源物在不同的细菌中要么作为 TA 要么作为 T6SS 效应物编码。我们的结果表明，由于 IS3 转座元件的作用，TA 型 TseTBg 同源物与某些 T6SS 相关基因的操纵子融合，导致新的 ORF（编码假设蛋白）进化。这可能导致伯克霍尔德氏菌中的 TA 转化为 T6SS 效应物。我们的研究表明，细菌可以将 TA 系统的毒素招募为 T6SS 武器，使其武器库多样化，以在细菌间竞争中占据优势。
