Review Article | Published:

The good viruses: viral mutualistic symbioses

Nature Reviews Microbiology volume 9, pages 99108 (2011) | Download Citation

Abstract

Although viruses are most often studied as pathogens, many are beneficial to their hosts, providing essential functions in some cases and conditionally beneficial functions in others. Beneficial viruses have been discovered in many different hosts, including bacteria, insects, plants, fungi and animals. How these beneficial interactions evolve is still a mystery in many cases but, as discussed in this Review, the mechanisms of these interactions are beginning to be understood in more detail.

Key points

  • Viruses have traditionally been thought of as pathogens, but many confer a benefit to their hosts and some are essential for the host life cycle.

  • The polydnaviruses of endoparasitoid wasps have evolved with their hosts to become essential. Many of the viral genes are now encoded in the host nucleus.

  • Endogenous retroviruses are abundant in many genomes of higher eukaryotes, and some have been involved in the evolution of their hosts, such as placental mammals.

  • Some mammalian viruses can protect their hosts from infection by related viruses or from disease caused by completely unrelated pathogens, such as bubonic plague.

  • Viruses can protect their hosts by killing off competitors, as is seen with the killer viruses in yeasts.

  • A fungal virus confers thermal tolerance to a plant in a complex symbiosis involving its fungal host and the plant that the fungus colonizes.

  • Several acute plant viruses confer conditional mutualism by enhancing drought tolerance in plants.

  • Insect viruses have numerous mutualistic relationships with their hosts; in addition, viruses play parts in bacterium–insect mutualisms.

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Acknowledgements

The author is grateful to colleagues for helpful discussions, especially R. Redman, F. Ryan and L. Villarreal, and to her current and former laboratory members T. Feldman, L. Márquez, M. Morsy and P. Xu.

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Affiliations

  1. Samuel Roberts Noble Foundation, Plant Biology Division, Ardmore, Oklahoma 73401, USA.  mroossinck@noble.org

    • Marilyn J. Roossinck

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The author declares no competing financial interests.

Glossary

Mutualistic

Pertaining to a symbiosis that is beneficial to all partners.

Provirus

Viral genomic DNA that has integrated into the genome of the host cell.

Symbiogenic

Pertaining to a new species: formed by the fusion of symbiotic organisms.

Antagonism

A symbiotic relationship in which one partner benefits at the expense of the other.

Commensalism

A symbiotic relationship in which one partner benefits and the other is unaffected.

Endoparasitoid

A specific type of parasitoid organism that spends a portion of its life within another organism.

Haemocoel

In arthropods, the space between the organs through which haemolymph circulates.

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https://doi.org/10.1038/nrmicro2491

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