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Endosymbiont DNA in endobacteria-free filarial nematodes indicates ancient horizontal genetic transfer

Samantha N McNulty1, Jeremy M Foster, Makedonka Mitreva

  • 1Infectious Diseases Division, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.

Plos One
|June 15, 2010
PubMed
Abstract

Insights

Filarial nematodes likely evolved with Wolbachia, a symbiotic microbe. Evidence suggests ancient Wolbachia DNA integrated into their genomes, influencing evolution and explaining why some species can survive without this essential symbiont.

Area of Science:

  • Microbiology
  • Genomics
  • Evolutionary Biology

Background:

  • Wolbachia are abundant endosymbionts found in many insects, spiders, mites, crustaceans, and filarial nematodes.
  • Filarial nematodes, including important human and animal pathogens, often depend on Wolbachia for survival and development.
  • The precise mechanisms of this interdependence and the existence of naturally Wolbachia-free filarial species remain unclear.

Purpose of the Study:

  • To investigate the genomic and transcriptomic evidence of Wolbachia in Wolbachia-free filarial nematodes.
  • To explore the evolutionary history and potential impact of Wolbachia on filarial nematode genomes.

Main Methods:

  • Genome sequencing using 454 pyrosequencing was performed on two Wolbachia-free filarial species: Acanthocheilonema viteae and Onchocerca flexuosa.
  • Quantitative reverse transcription PCR (qRT-PCR) was used to assess the expression of Wolbachia-like sequences.
  • In situ hybridization was employed to localize the expression of specific pseudogene transcripts.

Main Results:

  • Numerous Wolbachia-like DNA sequences were identified in both A. viteae (49 sequences) and O. flexuosa (114 sequences).
  • A significant portion of these sequences were found to be transcribed, with 30 in A. viteae and 56 in O. flexuosa.
  • Approximately half of the detected transcripts originated from pseudogenes, with two pseudogene transcripts specifically localized in the testes and developing embryos of both species.

Conclusions:

  • The findings strongly indicate that the ancestral filarial nematode was infected with Wolbachia.
  • Ancient Wolbachia endosymbionts likely contributed to the genome evolution of filarial nematodes.
  • Horizontally transferred Wolbachia DNA may account for the ability of certain filarial species to thrive independently of the endosymbiont.

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