Article

The good viruses: viral mutualistic symbioses.

Samuel Roberts Noble Foundation, Plant Biology Division, Ardmore, Oklahoma 73401, USA.
Nature Reviews Microbiology (Impact Factor: 23.32). 02/2011; 9(2):99-108. DOI: 10.1038/nrmicro2491
Source: PubMed

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.

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    ABSTRACT: Although viruses are almost always thought of as pathogens, most viruses probably do not cause disease, and some provide essential benefits to their hosts. Beneficial viruses are found in a wide variety of hosts including bacteria, insects, plants, fungi and other microbial eukaryotes, and humans and other animals. Beneficial viruses can confer tolerance to stress such as heat, cold and drought; they can prevent or attenuate infection by pathogenic microbes; they can act as bio-weapons to allow their hosts access to new territory; and they have been critical in the evolution of their hosts. In spite of their bad reputation, viruses could be used to benefit humans and their food sources in novel ways. Almost everything we know about viruses is related to their ability to cause disease in humans and their domesticated plants and animals. Recent metagenomics studies demonstrate the abundance of viruses in many different environments, and suggest that causing disease is not the normal lifestyle of viruses, and that most are probably benign 1-3 . Some are clearly beneficial 4. Why do we have such a bias in the scientific literature? The first described virus, Tobacco mosaic virus, caused disease in plants 5 . Perhaps this set the stage for viruses as malevolent agents, but listening to the news shows us that humans are inherently fascinated with the bad rather than the good. In addition, because viruses have been responsible for some very serious human diseases, such as polio, influenza, and AIDS, almost everyone is aware of their potential for devastating effects.

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