Baldridge Gerald D, Burkhardt Nicole Y, Simser Jason A, Kurtti Timothy J, Munderloh Ulrike G
Department of Entomology, University of Minnesota, St. Paul, Minnesota 55108, USA.
Appl Environ Microbiol. 2004 Nov;70(11):6628-36. doi: 10.1128/AEM.70.11.6628-6636.2004.
The transmission dynamics of Rocky Mountain spotted fever in Montana appears to be regulated by Rickettsia peacockii, a tick symbiotic rickettsia that interferes with transmission of virulent Rickettsia rickettsii. To elucidate the molecular relationships between the two rickettsiae and glean information on how to possibly exploit this interference phenomenon, we studied a major rickettsial outer membrane protein gene, ompA, presumed to be involved in infection and pathogenesis of spotted fever group rickettsiae (SFGR) but which is not expressed in the symbiont. Based on PCR amplification and DNA sequence analysis of the SFGR ompA gene, we demonstrate that R. peacockii is the most closely related of all known SFGR to R. rickettsii. We show that R. peacockii, originally described as East Side agent in Dermacentor andersoni ticks from the east side of the Bitterroot Valley in Montana, is still present in that tick population as well as in D. andersoni ticks collected at two widely separated locations in Colorado. The ompA genes of R. peacockii from these locations share three identical premature stop codons and a weakened ribosome binding site consensus sequence relative to ompA of R. rickettsii. The R. peacockii ompA promoter closely resembles that of R. rickettsii and is functional based on reverse transcription-PCR results. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting showed that OmpA translation products were not detected in cultured tick cells infected with R. peacockii. Double immunolabeling studies revealed actin tail structures in tick cells infected with R. rickettsii strain Hlp#2 but not in cells infected with R. peacockii.
落基山斑疹热在蒙大拿州的传播动态似乎受孔雀立克次氏体调节，孔雀立克次氏体是一种蜱共生立克次氏体，可干扰强毒力的立氏立克次氏体的传播。为了阐明这两种立克次氏体之间的分子关系，并收集有关如何利用这种干扰现象的信息，我们研究了一个主要的立克次氏体外膜蛋白基因ompA，该基因被认为与斑点热群立克次氏体（SFGR）的感染和发病机制有关，但在共生体中不表达。基于对SFGR ompA基因的PCR扩增和DNA序列分析，我们证明孔雀立克次氏体是所有已知SFGR中立氏立克次氏体关系最密切的。我们表明，最初在蒙大拿州比特鲁特谷东侧的安德逊革蜱中被描述为东侧病原体的孔雀立克次氏体，仍然存在于该蜱种群以及在科罗拉多州两个相距甚远的地点采集的安德逊革蜱中。相对于立氏立克次氏体的ompA，来自这些地点的孔雀立克次氏体的ompA基因共享三个相同的提前终止密码子和一个弱化的核糖体结合位点共有序列。孔雀立克次氏体ompA启动子与立氏立克次氏体的启动子非常相似，并且基于逆转录PCR结果具有功能。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和蛋白质免疫印迹表明，在感染孔雀立克次氏体的培养蜱细胞中未检测到OmpA翻译产物。双重免疫标记研究显示，感染立氏立克次氏体菌株Hlp#2的蜱细胞中有肌动蛋白尾结构，但感染孔雀立克次氏体的细胞中没有。
