A Sleek Genome, Except For All the Junk

© AAAS; E. Pennisi, Science, 295: 1809–11, 2002Wolbachia pipientis is a biological eye opener. This intracellular bacterium that colonizes insects and filarial nematodes kills male hosts but thrives in females, sometimes even influencing sexual determination. The recent completion of the W. pipientis genome reveals another unique quality: A streamlined genome without the loss of mobile elements and junk DNA."This finding was an enormous surprise," says Jonathan Eisen, investigator at

By | April 12, 2004

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© AAAS; E. Pennisi, Science, 295: 1809–11, 2002

Wolbachia pipientis is a biological eye opener. This intracellular bacterium that colonizes insects and filarial nematodes kills male hosts but thrives in females, sometimes even influencing sexual determination. The recent completion of the W. pipientis genome reveals another unique quality: A streamlined genome without the loss of mobile elements and junk DNA.

"This finding was an enormous surprise," says Jonathan Eisen, investigator at the Institute for Genomic Research, Rockville, Md., who together with Scott O'Neill, from the University of Queensland, Australia, formed a consortium to sequence the organism in 1999. Evolutionary forces typically shrink the genomes of intracellular bacteria, and junk DNA is generally thought to be lost with nonessential genes. But here, massive amounts are left over, says Eisen. "We argue that this is a symptom of inefficient natural selection in Wolbachia."

Seth Bordenstein, staff scientist at the Marine Biological Laboratory, Woods Hole, Mass., says the "finding debunks an emerging consensus that the genomes of obligate bacterial endosymbionts are perfectly streamlined," but also raises questions as to why so much mobile DNA remains. Regardless of the reason, Mark Taylor, Liverpool School of Tropical Medicine notes that "it will have an enormous impact and will change the way we research this symbiosis." He adds that the finding will spark practical applications including a "search for new antibiotics for filariasis."

- David Secko

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