Wide Dispersal and Possible Multiple Origins of Low-Copy-Number Plasmids in Rickettsia Species Associated with Blood-Feeding Arthropods
Wide Dispersal and Possible Multiple Origins of Low-Copy-Number Plasmids in Rickettsia Species Associated with Blood-Feeding Arthropods
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DOI：
10.1128/aem.02988-09
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发表时间：
2010-03-01
影响因子：
4.4
通讯作者：
Munderloh, Ulrike G.
中科院分区：
文献类型：
--
作者：
Baldridge, Gerald D.;Burkhardt, Nicole Y.;Munderloh, Ulrike G.
质粒是细菌的移动的遗传元件，其可以赋予重要的适应性特征，例如增加的毒力或抗生素抗性。本文报道了在立克次体属（立克次体目，立克次体科）的几种立克次体中质粒的存在，包括赤立立克次体（Rickettsiaakari）、安氏立克次体（Rickettsiaamblyommii）、雷氏立克次体（R.贝利河rhipicephali和REIS，肩突硬蜱的立克次体内共生体。所有立克次体都是从人类或北美和南美蜱中分离出来的。R.来自两大洲的parkeri分离物不具有质粒。我们现在已经证明了质粒在几乎所有的立克次体物种，我们已经调查了来自三大洲，这代表了四个主要的提出的系统发育组与吸血节肢动物。通过克隆两种“Ca.安氏立克次体分离株。立克次体帕拉质粒分配蛋白的系统发育分析表明多个帕拉基因起源和质粒不相容性组，与可能的多个质粒起源一致。对可能与宿主相适应的立克次体小分子热休克蛋白的系统发育分析表明，热休克蛋白2基因具有质粒特异性，而热休克蛋白1基因仅存在于“Ca.安氏立克次体（Rickettsia amblyommii），”R.猫河monacensis和R.孔雀，可能获得独立的热休克蛋白2基因。质粒拷贝数在7个立克次体物种范围从2.4到9.2每个染色体当量，通过实时定量PCR测定。质粒通过水平基因转移赋予遗传可塑性和宿主适应性特征，抵消专性细胞内细菌典型的还原基因组进化，可能在立克次体进化和流行病学中具有重要意义。
Plasmids are mobile genetic elements of bacteria that can impart important adaptive traits, such as increased virulence or antibiotic resistance. We report the existence of plasmids in Rickettsia (Rickettsiales; Rickettsiaceae) species, including Rickettsia akari, "Candidatus Rickettsia amblyommii," R. bellii, R. rhipicephali, and REIS, the rickettsial endosymbiont of Ixodes scapularis. All of the rickettsiae were isolated from humans or North and South American ticks. R. parkeri isolates from both continents did not possess plasmids. We have now demonstrated plasmids in nearly all Rickettsia species that we have surveyed from three continents, which represent three of the four major proposed phylogenetic groups associated with blood-feeding arthropods. Gel-based evidence consistent with the existence of multiple plasmids in some species was confirmed by cloning plasmids with very different sequences from each of two "Ca. Rickettsia amblyommii" isolates. Phylogenetic analysis of rickettsial ParA plasmid partitioning proteins indicated multiple parA gene origins and plasmid incompatibility groups, consistent with possible multiple plasmid origins. Phylogenetic analysis of potentially host-adaptive rickettsial small heat shock proteins showed that hsp2 genes were plasmid specific and that hsp1 genes, found only on plasmids of "Ca. Rickettsia amblyommii," R. felis, R. monacensis, and R. peacockii, were probably acquired independently of the hsp2 genes. Plasmid copy numbers in seven Rickettsia species ranged from 2.4 to 9.2 per chromosomal equivalent, as determined by real-time quantitative PCR. Plasmids may be of significance in rickettsial evolution and epidemiology by conferring genetic plasticity and host-adaptive traits via horizontal gene transfer that counteracts the reductive genome evolution typical of obligate intracellular bacteria.