The relapsing fever spirochete Borrelia hermsii and the Lyme disease spirochete Borrelia burgdorferi sensu stricto each produces an abundant, orthologous, outer membrane protein, Vtp and OspC, respectively, when transmitted by tick bite. Gene inactivation studies have shown that both proteins are essential for spirochete infectivity when transmitted by their respective tick vectors. Therefore, we transformed a vtp-minus mutant of B. hermsii with ospC from B. burgdorferi and examined the behavior of this transgenic spirochete in its soft tick vector Ornithodoros hermsi. IFA staining indicated up to 97.8 % of the transgenic B. hermsii upregulated OspC in the ticks’ salivary glands compared to no more than 12.8 % in the midgut, similar to our previous findings with wild-type B. hermsii producing Vtp. Transformation with ospC also restored B. hermsii infectivity to mice when fed upon by infected ticks. Previous sequence analysis of Vtp for 79 isolates and DNA samples of B. hermsii in our laboratory showed this protein is highly polymorphic with 9 divergent amino acid types, yet strikingly the signal peptide is identical among all samples and the same for all OspC signal peptides for B. burgdorferi and related species examined to date. Searches in multiple genome sequences for other species of relapsing fever spirochetes failed to find the same signal peptide sequence to help identify potential transmission-associated proteins. However, some candidate signal peptides with highly similar sequences were found and worthy of future efforts with other species. While OspC of B. burgdorferi restored infectivity to a Vtp-minus mutant of B. hermsii, the functions of these proteins are not known. Our results should stimulate investigators to search for orthologous transmission-associated proteins in other tick-borne spirochetes to better understand how this group of pathogens has coevolved with diverse tick vectors.

回归热螺旋体 Hermsii和莱姆病螺旋体Borrelia burgdorferi sensu stricto 在通过蜱叮咬传播时分别产生丰富的直系同源外膜蛋白 Vtp 和 OspC。基因失活研究表明，当通过各自的蜱载体传播时，这两种蛋白质对于螺旋体的传染性都是必不可少的。因此，我们用来自 B. burgdorferi 的 ospC 转化了B. hermsii的vtp - minus突变体，并检查了这种转基因螺旋体在其软蜱载体Ornithodoros hermsi中的行为。IFA 染色显示高达 97.8 % 的转基因B. hermsii与中肠中的不超过 12.8% 相比，蜱唾液腺中的 OspC 上调，这与我们之前对产生 Vtp的野生型B. hermsii的发现相似。当被感染的蜱虫喂食时，用ospC进行的转化也恢复了对小鼠的B. hermsii感染性。我们实验室对 79 个分离株和B. hermsii DNA 样品的 Vtp 序列分析表明，该蛋白质具有高度多态性，具有 9 种不同的氨基酸类型，但令人惊讶的是，所有样品中的信号肽相同，并且所有 OspC 信号肽都相同B. burgdorferi和迄今为止检查的相关物种。在多个基因组序列中搜索其他回归热螺旋体物种未能找到相同的信号肽序列来帮助识别潜在的传播相关蛋白。然而，发现了一些具有高度相似序列的候选信号肽，值得未来与其他物种一起努力。虽然B. burgdorferi的 OspC 恢复了B. hermsii的 Vtp-minus 突变体的感染性，但这些蛋白质的功能尚不清楚。我们的结果应该会刺激研究人员在其他蜱传螺旋体中寻找直系同源传播相关蛋白，以更好地了解这组病原体如何与不同的蜱载体共同进化。