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Science 21 August 2009:
Vol. 325. no. 5943, pp. 992 - 994
DOI: 10.1126/science.1174463
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Reports

Bacteriophages Encode Factors Required for Protection in a Symbiotic Mutualism

Kerry M. Oliver,1,* Patrick H. Degnan,2 Martha S. Hunter,3 Nancy A. Moran2

Bacteriophages are known to carry key virulence factors for pathogenic bacteria, but their roles in symbiotic bacteria are less well understood. The heritable symbiont Hamiltonella defensa protects the aphid Acyrthosiphon pisum from attack by the parasitoid Aphidius ervi by killing developing wasp larvae. In a controlled genetic background, we show that a toxin-encoding bacteriophage is required to produce the protective phenotype. Phage loss occurs repeatedly in laboratory-held H. defensa–infected aphid clonal lines, resulting in increased susceptibility to parasitism in each instance. Our results show that these mobile genetic elements can endow a bacterial symbiont with benefits that extend to the animal host. Thus, phages vector ecologically important traits, such as defense against parasitoids, within and among symbiont and animal host lineages.

1 Department of Entomology, University of Georgia, Athens, GA 30602, USA.
2 Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
3 Department of Entomology, University of Arizona, Tucson, AZ 85721, USA.

* To whom correspondence should be addressed. E-mail: kmoliver{at}uga.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
A strain of the bacterial symbiont Regiella insecticola protects aphids against parasitoids.
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