Analyzing host shift patterns of Wolbachia (Alphaproteobacteria) among arthropods using comparative genomics
by Marta Tischer
Date of Examination:2023-10-05
Date of issue:2024-05-28
Advisor:Prof. Dr. Christoph Bleidorn
Referee:Prof. Dr. Christoph Bleidorn
Referee:Prof. Dr. Mark Maraun
Persistent Address:
http://dx.doi.org/10.53846/goediss-10444
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Abstract
English
In this thesis, I investigated the host shift event and patterns of the endosymbiotic bacterium Wolbachia. I examined the molecular diversity and distribution of Wolbachia among arthropod communities of different terrestrial habitats, as soil and selected plants (Daucus carota, Medicago sativa, Salix caprea, Urtica dioica) in the area of Göttingen in central Germany. To increase the knowledge of Wolbachia diversity, genomics, and horizontal transmission, a main drive for host shifts, we screened freshly collected arthropods from different habitats. Within the arthropod community of host plants, we screened more than 900 morphospecies of arthropods, and approximately 200 arthropod morphotypes collected in the beech forest soil. We sequenced 150 samples infected with Wolbachia of 100 different arthropod host types with low-cover genomic sequencing (Illumina). We optimized the genomic library preparation workflow for infected arthropods and we adjusted bioinformatic approaches to obtain Wolbachia draft genomes from short-read sequencing output, which can be used in phylogenetic studies and can constitute a reference and input for further studies. We analyzed Wolbachia incidents, molecular diversity, and phylogeny of Wolbachia in arthropods inhabiting soil. Our results of these small-scale studies show a high diversity of supergroups among approximately 6 host clades and the possibility of new strains detected in two new host types, respectively from the Protura and Pseudoscorpion host. Further, we sequenced and assembled genomes of mentioned novel Wolbachia genomes, providing data on not previously known Wolbachia strains of undetermined supergroup affinity. Data from new genomes, combined with 46 previously published Wolbachia genomes, covering most of the known and described supergroups, were used for the robust and most up-to-date phylogenetic reconstruction on a whole genome dataset. Whole genome assemblies provide a higher insight into the details of the endosymbiotic genome, for example, the detection of the presence of bacterial vitamin operon. Phylogenies presented in this study are the results of analyses using conserved gene sequences, core genomes, or ortholog-based inference. Moreover, we focus on the genes corresponding to the “positive” effect of Wolbachia on its hosts, as biotin operon genes. We compared the results of biotin operon gene screening performed with PCR reaction for selected genes, with the results of low-covered genome sequencing. Our comparative analyses lead to results of two independent biotin operon pathways within the same Wolbachia-infected hosts, due to the viral component, specifically bacteriophage WO, known in Wolbachia. We investigated the horizontal movement of the biotin operon gene complex between Wolbachia strains and their hosts, with an assessment of the possible connection of the level of functionality of the operon, by interpreting and understanding host ecology, biology, and trophic level, which drives conclusions about the potential benefits of additional biotin vitamin supplementation. Presented findings and analyses provide additional data to the general pool of Wolbachia and host variations and increase an understanding of their co-evolution.
Keywords: Wolbachia, horizontal transmission, biotin operon, phage WO
