Abstract

Wolbachia pipientis is an alpha-proteobacterial, obligate intracellular microbe and arguably the most successful infection on our planet, colonizing 40-60% of insect species. Wolbachia are also present in most, but not all, filarial nematodes where they are obligate mutualists and are the targets for anti-filarial drug discovery. Although Wolbachia are related to important human pathogens they do not infect mammals, but instead are well known for their reproductive manipulations of insect populations, inducing the following phenotypes: male-killing, feminization, parthenogenesis induction, or cytoplasmic incompatibility (CI). The most common of these, CI, results in a sperm-egg incompatibility and increases the relative fecundity of infected females in a population. In the last decade, Wolbachia have also been shown to provide a benefit to insects, where the infection can inhibit RNA virus replication within the host. Wolbachia cannot be cultivated outside of host cells and no genetic tools are available in the symbiont, limiting approaches available to its study. This means that many questions fundamental to our understanding of Wolbachia basic biology remained unknown for decades. The tenth biennial international Wolbachia conference, "Wolbachia Evolution, Ecology, Genomics and Cell Biology: A Chronicle of the Most Ubiquitous Symbiont", was held on June 17-22, 2018, Salem, MA USA. In the review below we highlight the new science presented at the meeting, link it to prior efforts to answer these questions across the Wolbachia genus, and the importance to the field of symbiosis. The topics covered in this review are based on the presentations at the conference.

Highlights

  • Wolbachia pipientis is an alphaproteobacterial obligate intracellular microbe and arguably the most successful infection on our planet, colonizing 40% to 60% of insect species

  • With regards to what mechanism might explain RNA virus inhibition mediated by the symbiont, Manabu Ote suggested that RNAs might be generally targets for Wolbachia-mediated phenotypes, explaining pathogen blocking as a side effect of host-Wolbachia interaction, while Tamanash Bhattacharya of the Irene Newton laboratory presented data suggesting that Wolbachia spp. alter the expression of a host methyltransferase to epigenetically modify virus RNA genomes and won a presentation award [32]

  • Michael Turelli, in collaboration with Brandon Cooper, Will Conner, Ary Hoffman, and colleagues, discussed the predominant modes of Wolbachia acquisition, including the observation that Drosophila hosts diverged up to 50 million years ago have Wolbachia spp. that diverged only a few thousand years ago [63]. These results suggest that Wolbachia spp. rapidly invade new host species through either introgression or horizontal acquisition

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Summary

MOLECULAR MECHANISMS OF SYMBIOSIS

One major unifying theme emerged from the presentations, the attempt to discern the molecular mechanisms of symbiosis. Researchers have used models to try and make sense of the complex bidirectional incompatibility induced by the symbiont [1], have explored the influence of host and symbiont genotypes on the induced reproductive effects [2, 3], have studied the influence of environmental or ecological factors [4, 5], and have performed comparative genomics analyses [6] to try and identify the mechanism(s). Cytoplasmic incompatibility (CI) rescue was shown to be mediated by one of the same prophage WO genes which exist in an operon in the Wolbachia phage genome [10]. This arrangement is reminiscent of toxin-antitoxin operons, Dylan Shropshire of the Seth Bordenstein lab

Applied and Environmental Microbiology
Findings
CONCLUSIONS AND FUTURE DIRECTIONS
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