Toxins of toxin/antitoxin systems are inactivated primarily through promoter mutations
Toxins of toxin/antitoxin systems are inactivated primarily through promoter mutations
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DOI：
10.1111/jam.14414
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发表时间：
2019-09-01
影响因子：
4
通讯作者：
Wood, T. K.
中科院分区：
文献类型：
--
作者：
Fernandez-Garcia, L.;Kim, J. -S.;Wood, T. K.
鉴于毒素-抗毒素（TA）系统中某些毒素的毒性极大，我们很好奇细胞是如何沉默毒素的，如果抗毒素是灭活的，或者通过水平基因转移获得独立的毒素。方法和结果携带质粒pCA24N的大肠杆菌K12 BW25113在产生rar、MqsR、GhoT或Hha毒素3小时后，其生长曲线显示毒素失活。从这些培养的质粒中测序发现，毒素失活主要是由于启动子的一致缺失。对1000个大肠杆菌基因组的生物信息学分析证实了结构基因的缺乏突变，结果表明这四个毒素基因既保守又没有变化。对于那些质粒缺乏突变的菌株，进行单核苷酸多态性分析，确定染色体突变iraM和mhpR分别灭活毒素GhoT和MqsR/GhoT。我们发现，rralr （I型）、MqsR （II型）、GhoT （V型）和Hha （VII型）毒素的失活主要是通过毒素启动子失活的突变或通过染色体突变iraM和mhpR。本研究表明，主要影响毒素基因启动子而非毒素结构基因的突变可能使TA系统中的毒素失活。
Aims Given the extreme toxicity of some of the toxins of toxin-antitoxin (TA) systems, we were curious how the cell silences toxins, if the antitoxin is inactivated or independent toxins are obtained via horizontal gene transfer. Methods and Results Growth curves of Escherichia coli K12 BW25113 harbouring plasmid pCA24N to produce RalR, MqsR, GhoT or Hha toxins, showed toxin inactivation after 3 h. Sequencing plasmids from these cultures revealed toxin inactivation occurred primarily due to consistent deletions in the promoter. The lack of mutation in the structural genes was corroborated by a bioinformatics analysis of 1000 E. coli genomes which showed both conservation and little variability in the four toxin genes. For those strains that lacked a mutation in the plasmid, single nucleotide polymorphism analysis was performed to identify that chromosomal mutations iraM and mhpR inactivate the toxins GhoT and MqsR/GhoT respectively. Conclusion We find that the RalR (type I), MqsR (type II), GhoT (type V) and Hha (type VII) toxins are inactivated primarily by a mutation that inactivates the toxin promoter or via the chromosomal mutations iraM and mhpR. Significance and Impact of the Study This study demonstrates toxins of TA systems may be inactivated by mutations that primarily affect the toxin gene promoter instead of the toxin structural gene.