The Flag-2 locus, an ancestral gene cluster, is potentially associated with a novel flagellar system from Escherichia coli
The Flag-2 locus, an ancestral gene cluster, is potentially associated with a novel flagellar system from Escherichia coli
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DOI：
10.1128/jb.187.4.1430-1440.2005
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发表时间：
2005-02-01
影响因子：
3.2
通讯作者：
Pallen, MJ
中科院分区：
文献类型：
--
作者：
Ren, CP;Beatson, SA;Pallen, MJ
大肠杆菌K-12具有两个相邻的、趋异的、无启动子的鞭毛基因fhiA-mbhA，这两个基因在肠道沙门氏菌中不存在。通过生物信息学分析，我们发现这些基因是祖先44个基因簇的残余，并且能够编码一种新的鞭毛系统Flag-2。肠聚集性E. coli菌株042中，lfgC中存在移码，这可能使该菌株中的系统失活。平铺路径PCR研究表明，Flag-2簇存在于72个良好表征的ECOR菌株中的15个中。Flag-2系统类似于气单胞菌和弧菌的侧鞭毛系统，特别是在其明显依赖于RpoN方面。与传统的Flag-1鞭毛蛋白不同，Flag-2鞭毛蛋白显着缺乏序列多态性。Flag-2基因簇编码鞭毛III型分泌系统（包括专用的鞭毛σ-antisigma组合），从而将埃希氏菌/志贺氏菌中不同的III型分泌系统的数量提高到5个。Flag-2基因簇在E. coli及其近亲Citrobacter rodentium，结合其在S. enterica，表明它是在前两个物种从沙门氏菌分化后通过水平基因转移获得的。在鼠疫耶尔森氏菌、假结核耶尔森氏菌和紫色色杆菌中存在Flag-2样基因簇表明，同一物种中两种鞭毛系统的共存比以前怀疑的更常见。Flag-2基因簇未在研究的前10个埃希氏菌/志贺菌基因组序列中发现，这一事实强调了为这一重要的分类群维持一个充满活力的基因组测序计划的重要性。
Escherichia coli K-12 possesses two adjacent, divergent, promoterless flagellar genes, fhiA-mbhA, that are absent from Salmonella enterica. Through bioinformatics analysis, we found that these genes are remnants of an ancestral 44-gene cluster and are capable of encoding a novel flagellar system, Flag-2. In enteroaggregative E. coli strain 042, there is a frameshift in lfgC that is likely to have inactivated the system in this strain. Tiling path PCR studies showed that the Flag-2 cluster is present in 15 of 72 of the well-characterized ECOR strains. The Flag-2 system resembles the lateral flagellar systems of Aeromonas and Vibrio, particularly in its apparent dependence on RpoN. Unlike the conventional Flag-1 flagellin, the Flag-2 flagellin shows a remarkable lack of sequence polymorphism. The Flag-2 gene cluster encodes a flagellar type III secretion system (including a dedicated flagellar sigma-antisigma combination), thus raising the number of distinct type III secretion systems in Escherichia/Shigella to five. The presence of the Flag-2 cluster at: identical sites in E. coli and its close relative Citrobacter rodentium, combined with its absence from S. enterica, suggests that it was acquired by horizontal gene transfer after the former two species diverged from Salmonella. The presence of Flag-2-like gene clusters in Yersinia pestis, Yersinia pseudatuberculosis, and Chromobacterium violaceum suggests that coexistence of two flagellar systems within the same species is more common than previously suspected. The fact that the Flag-2 gene cluster was not discovered in the first 10 Escherichia/Shigella genome sequences studied emphasizes the importance of maintaining an energetic program of genome sequencing for this important taxonomic group.