Quek, Shannon
(2019)
Transcriptomic investigation of the Wolbachia symbiosis in larval stages of Brugia malayi.
PhD thesis, University of Liverpool.
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Abstract
The Wolbachia genus of bacteria is comprised of obligate intracellular endosymbionts that are known to infect arthropods and nematodes. Most filarial nematodes of humans host maintain Wolbachia endosymbionts in a mutualistic association that is essential for nematode development, reproduction and the longevity of the adult parasites. As a result, much research has gone into investigating Wolbachia’s role in adult nematodes, both in understanding the basis of the mutualistic relationship, as well as exploiting the endosymbiont as a target for treatment. Less attention has been applied to understanding Wolbachia’s role in the biology of larval stages of filarial parasites. To better characterise Wolbachia’s roles during these larval stages, RNA-sequencing technologies were employed to investigate the relationship between the parasitic filarial nematode Brugia malayi, and its Wolbachia endosymbiont during larval development and microfilarial transmission. This first involved the development of a manually curated, revised annotation of the Wolbachia genome using gene expression data, further corroborated by RT-qPCR and proteomics experiments. Second, the transcriptomes for both nematode and Wolbachia were then investigated across two major nematode developmental stages: the two weeks immediately after nematode infection into the mammalian host spanning the L3 to L4 developmental moult, and following Wolbachia depletion from B. malayi microfilariae during transmission to the mosquito vector. The reannotation of the Wolbachia endosymbiont genome resulted in the identification of 21 new protein coding genes, 5 instances of non-model translational events, and 3 functional RNAs. Several newly identified genes were predicted to be unique to the Wolbachia genus, with a potential role in Wolbachia-nematode interactions. The transcriptome of developing L3 to L4 stages demonstrates Wolbachia’s ability to undergo coordinated control over its carbon metabolism to enable rapid population growth. The consistent upregulation of metabolic pathways, such as haem, nucleotide biosynthesis and Type IV secretion systems, complements the nematode host transcriptome, which was focused predominantly on its own growth and development, as well as regulating Wolbachia population during the L4 stage. B. malayi microfilariae depleted of Wolbachia have a significantly reduced ability to infect the mosquito vector, with transcriptome analysis of treated and untreated nematodes identifying targeted downregulation of chitinase and V-type ATPase transcripts in the treated group. These targeted changes likely have a role in the nematode’s ability to successfully penetrate the vector’s midgut or achieve exsheathment. Taken together, these observations illustrate a complex and dynamic relationship that Wolbachia has with its nematode host, expanding to more than just a mutualist important for adult parasite longevity and reproduction.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Health and Life Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 08 Jan 2020 10:37 |
| Last Modified: | 19 Jan 2023 00:12 |
| DOI: | 10.17638/03066252 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3066252 |
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