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

沃尔巴克氏菌是一组甲蛋白细菌，在节肢动物和线虫宿主中以细胞内共生体的形式被发现。根据荟萃分析，估计高达52%的陆地节肢动物物种被感染。到目前为止，最常见的菌株是沃尔巴克氏菌超群A和B，节肢动物寄主之间的传播可以用水平转移来解释。然而，不同寄主之间的水平转移途径仍有待阐明。影响寄主转移模式的因素有三个：(1)寄主的系统发育关系；(2)寄主种群的地理分布；(3)寄主生态。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，我们最近可以发现，沃尔巴克氏菌的MLST分析对于这些问题可能根本没有用处，应该被基因组规模的方法所取代。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、生态学和生物地理对沃尔巴克氏菌株在节肢动物之间水平传播的相对贡献。为此，我们将筛选四种选定植物的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)紫花苜蓿节肢动物群落的沃尔巴克氏菌感染情况。在对沃尔巴克氏菌的存在进行PCR筛选后，将对包含宿主和沃尔巴克氏菌DNA的元基因组进行测序，并为选定的受感染节肢动物物种的个体进行组装。最后，比较系统发育学方法将被用来检验我们的三个工作假说：(I)共享相同寄主植物的受感染专家可能共享相似的沃尔巴克氏菌菌株；(Ii)与系统发育相关的受感染的通才可能共享相似的沃尔巴克氏菌；以及(Iii)相同或密切相关植物物种的节肢动物群落拥有不同大陆之间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.