The Decay of the Chromosomally Encoded ccdO157 Toxin-Antitoxin System in the Escherichia coli Species
The Decay of the Chromosomally Encoded ccdO157 Toxin-Antitoxin System in the Escherichia coli Species
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DOI：
10.1534/genetics.108.095190
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发表时间：
2009-04-01
期刊：
影响因子：
3.3
通讯作者：
Van Melderen, Laurence
中科院分区：
文献类型：
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作者：
Mine, Natacha;Guglielmini, Julien;Van Melderen, Laurence
毒素-抗毒素(TA)系统的起源和进化尚不清楚。TA系统在细菌染色体中含量丰富，被认为是源于水平基因转移的灵活基因组的一部分。为了深入了解TA系统的进化，我们分析了染色体编码的CD(O157)系统在395株大肠埃希菌自然分离株中的分布。它是在大肠杆菌O157：H7菌株中发现的，在该菌株中，它构成了两个核心基因(FOLA和APAH)之间的基因组岛。我们的研究表明，FOLA-APAH基因间隔区是可塑性的，容易受到外源DNA的插入。它可以由(I)重复的基因外回文(REP)序列，(Ii)ccd(O157)系统或其微妙变体，(Iii)含有与未知功能的ORF相关的ccd(O157)抗毒素残基的大DNA片段组成，或(Iv)变异体。其在CCDA(O157)残基中含有空气插入序列。对Cd(O157)变异体的序列分析和功能测试表明，69%的变异体由活性毒素和抗毒素组成，29%的变异体由活性抗毒素和失活毒素组成，2%的变异体两个ORF都是非活性的。分子进化分析表明，ccdB(O157)处于中性进化状态，表明该系统在大肠杆菌物种中不存在任何生物学作用。
The origin and the evolution of toxin-antitoxin (TA) systems remain to be uncovered. TA systems are abundant in bacterial chromosomes and are thought to be part of the flexible genome that originates from horizontal gene transfer. To gain insight into TA system evolution, we analyzed the distribution of the chromosomally encoded ccd(O157) system in 395 natural isolates of Escherichia coli. It was discovered in the E. coli O157:H7 strain in which it constitutes a genomic islet be tween two core genes (folA and apaH). Our study revealed that the folA-apaH intergenic region is plastic and Subject to insertion of foreign DNA. It could be composed (i) of a repetitive extragenic palindromic (REP) sequence, (ii) of the ccd(O157) System or subtle variants of it, (iii) of a large DNA piece that contained a ccd(O157) antitoxin remnant in association with ORFs of unknown function, or (iv) of a variant. of it containing air insertion sequence in the ccdA(O157) remnant. Sequence analysis and functional tests of the ccd(O157) variants revealed that 69% of the variants were composed of an active toxin and antitoxin, 29% were composed of an active antitoxin and an inactive toxin, and in 2% of the cases both ORFs were inactive. Molecular evolution analysis showed that ccdB(O157) is under neutral evolution, Suggesting that this system is devoid of any biological role in the E. coli species.