73. Parasite Invades Its Host’s DNA

By Nicholas Bakalar|Monday, January 14, 2008

In August, researchers reported that bacteria can transfer nearly their entire genome into the cells of a multicellular host. While such transfers have been ­observed before, the study leads researchers to believe that this type of genetic infiltration is much more common than previously suspected. It may be, they say, a novel evolutionary mechanism for organisms to pick up new genes and adapt them for new functions.

In a project led by John Werren of the University of Rochester, New York, the researchers experimented with Wolbachia pipientis, a type of symbiotic bac­terium that inhabits the testes and ovaries of many insects and worms.

When the researchers used antibiotics to kill all the Wolbachia living in a batch of fruit flies, they found that nearly all the parasite’s DNA stayed behind in the fly’s nuclear genome. Moreover, when they crossed male fruit flies carrying the ­inserted genome with Wolbachia-free ­females, they found that the genome was passed on from the father to offspring of both sexes. Females, too, could pass on the parasite’s DNA to their offspring.

In the wild, Wolbachia inserts can be found in fruit flies from Hawaii, Malaysia, Indonesia, and India, most likely due to a shared ancestor colonized long ago. It had been assumed that such lateral gene transfers were uncommon, but their existence in arthropods, the largest animal phylum, suggests that such transfers may be a significant evolutionary mechanism.

“About 30 percent of nematode and arthropod genomes contain Wolbachia inserts,” says biologist Julie Dunning Hotopp of the J. Craig Venter Institute, ­one of the researchers. “If you extrapolate, that’s a large number of organisms we’re talking about. These are two of the most ­abundant animal phyla. We don’t know yet how significant these transfers are. Do they actually lead to new working genes being acquired? Without knowing that, we can’t say how functionally significant the transfers are.”

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