Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 69978, Israel.
Int J Med Microbiol. 2010 Nov;300(7):470-81. doi: 10.1016/j.ijmm.2010.04.016. Epub 2010 May 26.
Legionella pneumophila, the causative agent of Legionnaires' disease, is known to be an intracellular pathogen of multiple species of protozoa and is assumed to have co-evolved with these organisms for millions of years. Genome sequencing of L. pneumophila strains has revealed an abundance of eukaryotic-like proteins (ELPs). Here, we study the evolution of these ELPs, in order to investigate their origin. Thirty-four new ELPs were identified, based on a higher similarity to eukaryotic proteins than to bacterial ones. Phylogenetic analyses demonstrated that both lateral gene transfer from eukaryotic hosts and bacterial genes that became eukaryotic-like by gradual adaptation to the intracellular milieu or gene fragment acquisition, contributed to the existing repertoire of ELPs, which comprise over 3% of the putative proteome of L. pneumophila strains. A PCR survey of 72 L. pneumophila strains showed that most ELPs were conserved in nearly all of these strains, indicating that they are likely to play important roles in this species. Genes of different evolutionary origin have distinct patterns of selection, as reflected by their ratio of a synonymous vs. synonymous mutations. One ELP is common to several strains of Legionella, but outside this genus has homologs only in Acanthamoeba polyphaga mimivirus, indicating that gene exchange involving eukaryotic viruses and intracellular bacterial pathogens may also contribute to the evolution of virulence in either or both of these groups of organisms. Information on selection patterns and eukaryotic-like status was combined as a novel approach to predict type IV secretion system effectors of Legionella, which represent promising targets for future study.
嗜肺军团菌是军团病的病原体，已知它是多种原生动物的细胞内病原体，并且被认为与这些生物体共同进化了数百万年。嗜肺军团菌菌株的基因组测序揭示了大量真核样蛋白（ELPs）。在这里，我们研究这些 ELP 的进化，以研究它们的起源。根据与真核蛋白的相似性高于与细菌的相似性，基于 34 种新的 ELP 被鉴定出来。系统发育分析表明，真核宿主的侧向基因转移以及通过逐渐适应细胞内环境或基因片段获得而变得真核样的细菌基因，都有助于现有的 ELP 库的形成，这占了嗜肺军团菌菌株假定蛋白质组的 3%以上。对 72 株嗜肺军团菌的 PCR 调查显示，这些 ELP 在几乎所有这些菌株中都保守，表明它们可能在该物种中发挥重要作用。不同进化起源的基因具有不同的选择模式，这反映在它们的同义与同义突变的比例上。一种 ELP 存在于几种军团菌菌株中，但在该属之外，只有在变形虫多形拟病毒中才有同源物，这表明涉及真核病毒和细胞内细菌病原体的基因交换也可能有助于这两个生物体群体中的任何一个或两者的毒力进化。选择模式和真核样状态的信息被组合在一起，作为一种预测军团菌 IV 型分泌系统效应物的新方法，这些效应物是未来研究的有前途的目标。
