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Abstract：
Streptococcus gallolyticus subsp. gallolyticus (SGG) is an opportunistic bacterial pathogen strongly associated with colorectal cancer. Here, through comparative genomics analysis, we demonstrated that the genetic locus encoding the type VIIb secretion system (T7SSb) machinery is uniquely present in SGG in two different arrangements. SGG UCN34 carrying the most prevalent T7SSb genetic arrangement was chosen as the reference strain. To identify the effectors secreted by this secretion system, we inactivated the essC gene encoding the motor of this machinery. A comparison of the proteins secreted by UCN34 wild type and its isogenic ΔessC mutant revealed six T7SSb effector proteins, including the expected WXG effector EsxA and three LXG-containing proteins. In this work, we characterized an LXG-family toxin named herein TelE promoting the loss of membrane integrity. Seven homologs of TelE harboring a conserved glycine zipper motif at the C terminus were identified in different SGG isolates. Scanning mutagenesis of this motif showed that the glycine residue at position 470 was crucial for TelE membrane destabilization activity. TelE activity was antagonized by a small protein TipE belonging to the DUF5085 family. Overall, we report herein a unique SGG T7SSb effector exhibiting a toxic activity against nonimmune bacteria. IMPORTANCE In this study, 38 clinical isolates of Streptococcus gallolyticus subsp. gallolyticus (SGG) were sequenced and a genetic locus encoding the type VIIb secretion system (T7SSb) was found conserved and absent from 16 genomes of the closely related S. gallolyticus subsp. pasteurianus (SGP). The T7SSb is a bona fide pathogenicity island. Here, we report that the model organism SGG strain UCN34 secretes six T7SSb effectors. One of the six effectors named TelE displayed a strong toxicity when overexpressed in Escherichia coli. Our results indicate that TelE is probably a pore-forming toxin whose activity can be antagonized by a specific immunity protein named TipE. Overall, we report a unique toxin-immunity protein pair and our data expand the range of effectors secreted through T7SSb.
摘要：
溶胆链球菌亚种。胆溶菌（SGG）是一种与结直肠癌密切相关的机会性细菌病原体。这里,通过比较基因组学分析，我们证明了编码VIIb型分泌系统（T7SSb）机制的遗传基因座以两种不同的排列独特地存在于SGG中。选择携带最普遍的T7SSb遗传排列的SGGUCN34作为参考菌株。为了确定该分泌系统分泌的效应物，我们灭活了编码这种机器马达的essC基因。UCN34野生型及其等基因ΔessC突变体分泌的蛋白质的比较揭示了六个T7SSb效应蛋白，包括预期的WXG效应物EsxA和三种含LXG的蛋白。在这项工作中,我们表征了本文命名为TelE的LXG家族毒素促进膜完整性丧失。在不同的SGG分离株中鉴定了在C末端具有保守的甘氨酸拉链基序的TelE的七个同源物。该基序的扫描诱变显示位置470处的甘氨酸残基对于TelE膜去稳定活性是至关重要的。TelE活性被属于DUF5085家族的小蛋白TipE拮抗。总的来说,我们在此报告了一种独特的SGGT7SSb效应物,其对非免疫细菌具有毒性活性.在这项研究中的重要性，38例临床分离的溶胆链球菌亚种。对胆溶菌（SGG）进行了测序，发现编码VIIb型分泌系统（T7SSb）的遗传基因座保守，并且在密切相关的胆溶菌亚种的16个基因组中不存在。巴氏杆菌（SGP）。T7SSb是一个真正的致病性岛。这里,我们报道了模型生物SGG菌株UCN34分泌六个T7SSb效应子。名为TelE的六种效应子之一在大肠杆菌中过表达时显示出强毒性。我们的结果表明，TelE可能是一种成孔毒素，其活性可被称为TipE的特异性免疫蛋白拮抗。总的来说,我们报道了一个独特的毒素-免疫蛋白对,我们的数据扩大了通过T7SSb分泌的效应物的范围.
