Analysing host-shift patterns of Wolbachia strains (Alphaproteobacteria) using comparative genomics

沃尔巴克氏体是一组在节肢动物和线虫宿主中作为细胞内共生体发现的α变形菌。根据荟萃分析，估计多达52%的陆生节肢动物物种受到感染。到目前为止，最常见的菌株是沃尔巴克氏体超群A和B，在节肢动物宿主之间的传播被解释为水平转移。然而，不同寄主之间的水平转移途径仍有待阐明。本文讨论了影响寄主迁移模式的三个不同因素：(1)寄主的系统发育关系；东道国人口的地理分布；（三）宿主生态学。讨论了这些因素的相对重要性和贡献，基于多位点序列分型（MLST）的比较系统发育分析得出了不一致的结果。然而，我们最近可以证明沃尔巴克氏体的MLST分析可能对这些问题根本没有用，应该被基因组尺度的方法所取代。在拟议的项目中，我们将使用系统发育学方法来比较系统发育、生态学和生物地理学对沃尔巴克氏体菌株在节肢动物之间水平传播的相对贡献。为此，我们将筛选四种节肢动物群落的感染状况。此外，我们还将比较美国（肯塔基州）和欧洲（德国）苜蓿节肢动物群落沃尔巴克氏体感染情况。在对沃尔巴克氏体进行PCR筛选后，将对选定的受感染节肢动物个体进行包含宿主和沃尔巴克氏体DNA的宏基因组测序和组装。最后，比较系统发育方法将用于测试我们的三个工作假设：(1)共享同一寄主植物的受感染专家可能具有相似的沃尔巴克氏体菌株；（II）与系统发育相关的感染多面手可能具有相似的沃尔巴克氏体；(3)相同或亲缘关系较近的植物节肢动物群落中存在不同大陆的沃尔巴克氏菌菌株。

Wolbachia is a group of Alphaproteobacteria found as intracellular endosymbionts in arthropod and nematode hosts. Based on meta-analyses, up to 52% of all terrestrial arthropod species are estimated to be infected. By far the most common strains are Wolbachia supergroup A and B and the spread among arthropod hosts has been explained by horizontal transfer. However, pathways of horizontal transfer between different hosts remain to be elucidated. Three different factors have been discussed influencing host shift patterns: (I) Phylogenetic relationships of hosts; (II) Geographic distribution of host populations; (III) Host ecology. The relative importance and contributions of these factors are discussed and comparative phylogenetic analyses based on multi-locus sequence typing (MLST) yielded incongruent results. However, we could recently show that Wolbachia MLST analyses may not be useful at all for such questions and should be replaced by genome-scale approaches.Within the proposed project we will use a phylogenomic approach to compare the relative contribution of phylogeny, ecology, and biogeography on horizontal transmission of Wolbachia strains among arthropods. For this purpose we will screen the infection status of arthropod communities of four selected plant species. Moreover, we will additionally compare Wolbachia infections of alfalfa arthropod communities between the USA (Kentucky) and Europe (Germany). After PCR screening for the presence of Wolbachia, metagenomes comprising host and Wolbachia DNA will be sequenced and assembled for selected individuals of infected arthropod species. Finally, comparative phylogenetic approaches will be used to test our three working hypotheses: (I) Infected specialists that share the same hostplant are likely to share similar Wolbachia strains; (II) Phylogenetically related infected generalists are likely to share similar Wolbachia; and (III) Arthropod communities of the same or closely related plant species harbor Wolbachia strains that differ between continents.