Weller S J, Baldridge G D, Munderloh U G, Noda H, Simser J, Kurtti T J
Department of Entomology and J.F. Bell Museum of Natural History, University of Minnesota, St. Paul 55108, USA.
J Clin Microbiol. 1998 May;36(5):1305-17. doi: 10.1128/JCM.36.5.1305-1317.1998.
A rickettsial isolate (isolate MOAa) belonging to the spotted fever group (SFG) was obtained from the lone star tick Amblyomma americanum. We used PCR to characterize the genes for the rickettsial outer membrane proteins rOmpA and rOmpB. We sequenced the PCR products (domains I of both the rompA gene and the rompB gene) of MOAa and WB-8-2, another rickettsial isolate from A. americanum. To place MOAa and WB-8-2 and two other nonpathogenic isolates (Rickettsia rickettsii Hip2 and Rickettsia montana M5/6) with respect to their putative sister species, we included them in a phylogenetic analysis of 9 Rickettsia species and 10 Rickettsia strains. Our phylogenetic results implied three evolutionary lineages of SFG rickettsiae and that WB-8-2 and MOAa were most closely related to R. montana. New World isolates were not the most closely related to each other (they did not form a clade). Rather, our results supported four independent origins (introductions) of rickettsiae into North America from different Old World regions. The results of our phylogenetic analysis did not support the hypothesis of a stable coevolution of rickettsiae and their tick hosts. Finally, we examined the rompA gene of a nonpathogenic rickettsial symbiont isolated from the tick Ixodes scapularis. In a phylogenetic analysis, the symbiont was placed as the sister to R. montana and its isolates. The relationship of this symbiont to R. montana raised questions as to the potential origin of pathogenic SFG rickettsiae from nonpathogenic tick symbionts, or vice versa.
从美洲钝眼蜱中获得了一株属于斑点热群（SFG）的立克次氏体分离株（分离株MOAa）。我们使用聚合酶链反应（PCR）来鉴定立克次氏体外膜蛋白rOmpA和rOmpB的基因。我们对MOAa和WB - 8 - 2（另一种从美洲钝眼蜱中分离得到的立克次氏体分离株）的PCR产物（rOmpA基因和rOmpB基因的结构域I）进行了测序。为了确定MOAa、WB - 8 - 2以及另外两个非致病性分离株（立氏立克次氏体Hip2和蒙大拿立克次氏体M5/6）与其假定的姐妹物种的关系，我们将它们纳入了对9种立克次氏体物种和10种立克次氏体菌株的系统发育分析中。我们的系统发育结果表明SFG立克次氏体有三个进化谱系，并且WB - 8 - 2和MOAa与蒙大拿立克次氏体关系最为密切。新世界的分离株彼此之间并非关系最为密切（它们没有形成一个分支）。相反，我们的结果支持立克次氏体从不同的旧世界区域四次独立传入北美洲的观点。我们的系统发育分析结果不支持立克次氏体与其蜱宿主稳定协同进化的假说。最后，我们检测了从肩突硬蜱中分离出的一种非致病性立克次氏体共生菌的rOmpA基因。在系统发育分析中，该共生菌被定位为蒙大拿立克次氏体及其分离株的姐妹种。这种共生菌与蒙大拿立克次氏体的关系引发了关于致病性SFG立克次氏体是否可能起源于非致病性蜱共生菌，或者反之亦然的问题。
