Fifty shades of bacterial endosymbionts and some of them still remain a mystery: Wolbachia and Cardinium in oribatid mites (Acari: Oribatida)

Further evidence of low infection frequencies of Wolbachia in soil arthropod communities

Endosymbiotic Alphaproteobacteria of the genus Wolbachia are exclusively transferred maternally from mother to offspring, but horizontal transfer across species boundaries seems to be frequent as well. However, the (ecological) mechanisms of how these bacteria are transferred between distantly related arthropod hosts remain unclear. Based on the observation that species that are part of the same ecological community often also share similar Wolbachia strains, host ecology has been hypothesized as an important factor enabling transmission and a key factor in explaining the global distribution of Wolbachia lineages. In this study, we focus on the diversity and abundance of Wolbachia strains in soil arthropods, a so far rather neglected community. We screened 82 arthropod morphotypes collected in the beech forest (dominated by Fagus sp.) soil in the area of Göttingen in central Germany for the presence of Wolbachia. By performing a PCR screen with Wolbachia-MLST markers (coxA, dnaA, fbpA, ftsZ, gatB, and hcpA), we found a rather low infection frequency of 12,2%. Additionally, we performed metagenomic screening of pooled individuals from the same sampling site and could not find evidence that this low infection frequency is an artefact due to PCR-primer bias. Phylogenetic analyses of the recovered Wolbachia strains grouped them in three known supergroups (A, B, and E), with the first report of Wolbachia in Protura (Hexapoda). Moreover, Wolbachia sequences from the pseudoscorpion Neobisium carcinoides cluster outside the currently known supergroup diversity. Our screening supports results from previous studies that the prevalence of Wolbachia infections seems to be lower in soil habitats than in above-ground terrestrial habitats. The reasons for this pattern are not completely understood but might stem from the low opportunity of physical contact and the prevalence of supergroups that are less suited for horizontal transfer.

Wolbachia supergroup A in Enoplognatha latimana (Araneae: Theridiidae) in Poland as an example of possible horizontal transfer of bacteria

Wolbachia (phylum Pseudomonadota, class Alfaproteobacteria, order Rickettsiales, family Ehrlichiaceae) is a maternally inherited bacterial symbiont infecting more than half of arthropod species worldwide and constituting an important force in the evolution, biology, and ecology of invertebrate hosts. Our study contributes to the limited knowledge regarding the presence of intracellular symbiotic bacteria in spiders. Specifically, we investigated the occurrence of Wolbachia infection in the spider species Enoplognatha latimana Hippa and Oksala, 1982 (Araneae: Theridiidae) using a sample collected in north-western Poland. To the best of our knowledge, this is the first report of Wolbachia infection in E. latimana. A phylogeny based on the sequence analysis of multiple genes, including 16S rRNA, coxA, fbpA, ftsZ, gatB, gltA, groEL, hcpA, and wsp revealed that Wolbachia from the spider represented supergroup A and was related to bacterial endosymbionts discovered in other spider hosts, as well as insects of the orders Diptera and Hymenoptera. A sequence unique for Wolbachia supergroup A was detected for the ftsZ gene. The sequences of Wolbachia housekeeping genes have been deposited in publicly available databases and are an important source of molecular data for comparative studies. The etiology of Wolbachia infection in E. latimana is discussed.