The evolution of the flagellar assembly pathway in endosymbiotic bacterial genomes
The evolution of the flagellar assembly pathway in endosymbiotic bacterial genomes
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DOI：
10.1093/molbev/msn153
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发表时间：
2008-09-01
影响因子：
10.7
通讯作者：
Fares, Mario A.
中科院分区：
文献类型：
--
作者：
Toft, Christina;Fares, Mario A.
基因组收缩是大多数细胞内病原体和共生体的共同特征。减少基因组大小是细胞内生物保存和避免维持昂贵的冗余生物过程的最具特征的进化方式之一。昆虫的内共生细菌是完成生物经济的例子，因为它们的基因组急剧减少。这些细菌是不动的，它们的生化过程与宿主的生化过程密切相关。由于这种关系，这些细菌中的许多过程要么已经丢失，要么已经经历了大规模的重塑，以适应细胞内共生的生活方式。这种变化的一个例子是鞭毛结构，它对细菌的运动和传染性至关重要。我们的分析表明，负责鞭毛组装的基因在大多数γ -变形杆菌的细胞内共生体中部分或完全丢失。比较基因组分析表明，鞭毛基因在昆虫内共生细菌中有差异丢失。在大多数内共生体中，只保留了鞭毛组装途径（III型分泌系统和基底体）中参与蛋白质输出的蛋白质，而参与构建鞭毛丝和鞭毛钩的蛋白质仅在少数情况下被保留，这表明该途径的功能目的发生了变化。在一些内共生生物中，控制蛋白质输出开关和鱼钩长度的基因发生了功能上的分化。根据我们的研究结果，我们认为鞭毛的基因在功能上已经分化，专门负责从细菌向宿主输出蛋白质。
Genome shrinkage is a common feature of most intracellular pathogens and symbionts. Reduction of genome sizes is among the best-characterized evolutionary ways of intracellular organisms to save and avoid maintaining expensive redundant biological processes. Endosymbiotic bacteria of insects are examples of biological economy taken to completion because their genomes are dramatically reduced. These bacteria are nonmotile, and their biochemical processes are intimately related to those of their host. Because of this relationship, many of the processes in these bacteria have been either lost or have suffered massive remodeling to adapt to the intracellular symbiotic lifestyle. An example of such changes is the flagellum structure that is essential for bacterial motility and infectivity. Our analysis indicates that genes responsible for flagellar assembly have been partially or totally lost in most intracellular symbionts of gamma-Proteobacteria. Comparative genomic analyses show that flagellar genes have been differentially lost in endosymbiotic bacteria of insects. Only proteins involved in protein export within the flagella assembly pathway (type III secretion system and the basal body) have been kept in most of the endosymbionts, whereas those involved in building the filament and hook of flagella have only in few instances been kept, indicating a change in the functional purpose of this pathway. In some endosymbionts, genes controlling protein-export switch and hook length have undergone functional divergence as shown through an analysis of their evolutionary dynamics. Based on our results, we suggest that genes of flagellum have diverged functionally as to specialize in the export of proteins from the bacterium to the host.