Like an overprotective father, a bacterium known for controlling the reproductive patterns of the insects it infects turns out also to shield fruit flies from deadly viral infections.
New research shows that Drosophila flies infected with Wolbachia bacteria fare better than uninfected flies against several killer viruses.
Wolbachia - which plagues two-thirds of all insect species - is best known for its gender-bending effects. The bacteria are transmitted in eggs but not sperm, and males are therefore a reproductive dead-end from their point of view.
In some insects, Wolbachia kills males and converts developing males to females. The bacteria can also ensure that matings between infected males and uninfected females produce no offspring, causing the "destruction of uninfected lineages", says John Jaenike, an evolutionary geneticist at the University of Rochester, New York.
The upside of infection
But evolution cannot tolerate such a one-sided relationship for long. For Drosophila, there has to be some positive effect of being infected with Wolbachia, says Karyn Johnson, an insect virologist at the University of Queensland in Brisbane, Australia, who led the new study.
While hunting for genes that protected Drosophila from viral infection in general, she found a virus-resistant fly strain that turned out to be infected with Wolbachia. The tainted fly strain was supplied by a colleague, Scott O'Neill, who studies the bacteria in his lab. "We didn't go looking for Wolbachia," Johnson says.
Following up on the serendipitous discovery, her team found that flies not infected with Wolbachia lasted less than a week when exposed to a Drosophila virus, while flies carrying Wolbachia lived up to two weeks. For two other insect viruses, the difference was even starker, with Wolbachia-infected flies lasting weeks longer.
This extra lease of life is critical to the flies, occurring when they are at the peak of the reproductive cycle, says Jaenike, who was not involved in the study. He wonders whether other insects experience the same benefit from Wolbachia infection, noting that the bacteria's effect on most insect species remains unknown.
Journal reference: Science (DOI: 10.1126/science.1162418)
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