Living off the Fat of the Cell

SAN FRANCISCO, CALIFORNIA--A sexually transmissible microbe may have a unique way of reproducing: by ordering the cells in which it lives to produce tiny halos of fat. The finding may help explain why the bug, Chlamydia trachomatis, is also implicated in cardiovascular problems, researchers say.

Despite the havoc C. trachomatis wreaks on humans, little is known about how it thrives within our cells. Scientists do know that Chlamydia reproduces within cellular pockets called vacuoles and needs fats to do so. That's why cell biologists Yadunanda Budigi Kumar and Raphael Valdivia of Duke University in Durham, North Carolina, wondered if it stole fats from droplets in the cell called lipid bodies--little known structures once thought to be merely storage vessels but recently implicated in more active roles, such as moving cellular components around.

When the team engineered yeast cells to produce a variety of Chlamydia's proteins, they found that two of the proteins gathered in lipid bodies. In further studies, the team discovered that in mammalian cells, the same bodies formed a halo around the vacuoles in which Chlamydia resided.

Was Chlamydia using these fats to replicate? To find out, the researchers measured how much lipids the cells produced over time. About two days after infection, the amount of lipids in the cells rose five-fold, suggesting that the bugs were somehow stimulating fat production. In addition, giving infected cells a drug that prevented lipid body formation prevented the bacteria from reproducing, the researchers reported here 11 December at a meeting of the American Society for Cell Biology. Its fat-stimulating properties may explain why chronic Chlamydial infections appear to be linked to clogged arteries and heart disease, the researchers speculate.

Microbiologist Ted Hackstadt of the National Institute of Allergy and Infectious Diseases Rocky Mountain Laboratories in Hamilton, Montana, calls the work "promising." He says the researchers "took an innovative approach" to studying the bug and came up with a "pretty novel mechanism" for how Chlamydia grows within cells. "I don't know of any other infectious pathogen that does this."

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