Chlamydia's Secrets Laid Bare

Scientists have sequenced the entire genome of Chlamydia trachomatis, the enigmatic bacterium that's the leading cause of venereal disease in the United States. The work, described in tomorrow's Science, offers surprising insights into the bug that could lead to better treatments and perhaps even vaccines.

Nearly 4 million new cases of Chlamydia are reported each year in the United States, says lead author Richard Stephens, a microbial geneticist at the University of California, Berkeley. It can cause pelvic infections, ectopic pregnancy, and sterility if untreated. In Africa and Asia, where the bacterium spreads through hand-eye contact among children rather than sexual intimacy, it is a leading cause of blindness. But efforts to create a vaccine have been stymied by the parasite's refusal to survive in a petri dish.

Stephens's team took 18 months to sequence the bacterium's 1,042,519 base pairs. Surprises include the discovery of about 20 eukaryotic genes; other bacteria that have been sequenced have had few, if any, such genes. "This paints a picture of an intimate and long evolution with eukaryotic cells," says Stephens. The finding goes to the question of how it evolved its parasitic lifestyle. Many of these eukaryotic genes resemble plant genes--hinting that Chlamydia's ancestors may have first parasitized plantlike microorganisms. Also intriguing is that Chlamydia can make ATP, the basic fuel for any cell. "We've always thought the reason Chlamydia could only live inside a eukaryote was that it required ATP from the host," says Stephens.

The new genome map "will facilitate and stimulate a lot more research on Chlamydia," predicts Thomas Hatch, a microbiologist at the University of Tennessee Medical School in Memphis. The genetic code also holds clues to Chlamydia's surface proteins, which Stephens says should give researchers new targets for vaccines, diagnostic tests, and drugs.