Transcriptomic and Proteomic Analyses of a Wolbachia-Free Filarial Parasite Provide Evidence of Trans-Kingdom Horizontal Gene Transfer

Abstract

Most filarial parasites in the subfamilies Onchocercinae and Dirofilariinae depend on Wolbachia endobacteria to successfully carry out their life cycle. Recently published data indicate that the few Wolbachia-free species in these subfamilies were infected in the distant past and have subsequently shed their endosymbionts. We used an integrated transcriptomic and proteomic analysis of Onchocerca flexuosa to explore the molecular mechanisms that allow worms of this species to survive without a bacterial partner. Roche/454 sequencing of the adult transcriptome produced 16,814 isogroup and 47,252 singleton sequences that are estimated to represent approximately 41% of the complete gene set. Sequences similar to 97 Wolbachia genes were identified from the transcriptome, some of which appear on the same transcripts as sequences similar to nematode genes. Computationally predicted peptides, including those with similarity to Wolbachia proteins, were classified at the domain and pathway levels in order to assess the metabolic capabilities of O. flexuosa and compare against the Wolbachia-dependent model filaria, Brugia malayi. Transcript data further facilitated a shotgun proteomic analysis of O. flexuosa adult worm lysate, resulting in the identification of 1,803 proteins. Three of the peptides detected by mass spectroscopy map to two ABC transport-related proteins from Wolbachia. Antibodies raised to one of the Wolbachia-like peptides labeled a single 38 kDa band on Western blots of O. flexuosa lysate and stained specific worm tissues by immunohistology. Future studies will be required to determine the exact functions of Wolbachia-like peptides and proteins in O. flexuosa and to assess their roles in worm biology.

Horizontal gene transfer in the acquisition of novel traits by metazoans

“…On the other hand, gene transfers from endosymbionts to Onchocercids nematode genomes can be facilitated by the close association between bacteria and nematode germ line cells at the female stage. A recent study [32] shows the presence of transcriptionally active Wolbachia-related genes in Wolbachia-free Onchocercid genomes suggesting an ancient transfer occurring before the loss of the symbiont in these nematodes.…”

An insight into the sialome of the frog biting fly, Corethrella appendiculata

“…These included several ribosomal proteins, elongation factors, ATP synthases, and other proteins, indicating C. appendiculata to have a Wolbachia symbiont, as commonly found with many insect species (Stouthamer et al, 1999). It is also possible and more likely (due to the polyadenylation selection of the RNA used for sequencing) that these sequences derive from Wolbachia genes that became integrated into the fly genome, an increasingly common finding as insect and other invertebrate genomic sequences accumulate (Klasson et al, 2009; McNulty et al, 2012; Woolfit et al, 2009). …”

Manipulation of Arthropod Sex Determination by Endosymbionts: Diversity and Molecular Mechanisms

“…Comparison of transcriptomes and proteomes of infected and uninfected hosts may also be rewarding [e.g. McNulty et al, 2012]. Moreover, the integration of knowledge about evolutionary dynamics and genomic data should make it possible to identify genomic signatures that can lead to the identification of genes involved in host reproduction and sex determination manipulation.…”