Bring on the germs. Flies exposed to bacteria at a young age live longer than their germ-free counterparts.

Live Clean, Die Young

The fountain of youth it's not, but early exposure to bacteria makes fruit flies live longer. The results suggest that bacteria affect genes that control life span, and that overuse of antibiotics could harm well-being and longevity in animals and perhaps even in humans.

As animals and people age, overall immunity weakens, and old animals are more likely to die from infections. That simple fact, however, turns out to obscure a puzzling detail. Two years ago, while investigating the effect of immune genes on longevity, molecular geneticist Ted Brummel of Sam Houston State University in Huntsville, Texas, Seymour Benzer of the California Institute of Technology in Pasadena, and their colleagues found that middle-aged fruit flies turned up the expression of an antibacterial gene just as they began to die off more frequently. Suspecting that exposure to bacteria might shorten the flies' life span, the researchers wondered what would happen if they eliminated bacteria from inside and outside the fly.

To do that, they soaked fruit fly eggs briefly in bleach, washed them in alcohol, and grew them in sterilized jars with sterilized food--treatments that prevented the flies from picking up the menagerie of bacteria that usually climb aboard early in life. To their surprise, the disinfected flies lived only two-thirds as long as normal flies. The researchers got essentially the same results when they treated the flies early in life with antibiotics, confirming that the exposure to bacteria was necessary for a long life. Probing further, the researchers found that timing was important. Bacteria extended life span only if the fruit flies were exposed within 4 days of hatching; in fact, removing bacteria with antibiotics made old fruit flies live 10% longer. And the genetic makeup of the flies also mattered, because lifelong antibiotic treatment caused one normally long-lived mutant line to die at the same age as normal flies given antibiotics--in other words, its life span was extended only in the presence of bacteria, the researchers report in this week's issue of Proceedings of the National Academy of Sciences. Now, the researchers are doing experiments to pinpoint which genes interact with bacteria to lengthen life, Brummel says.

"I'm pretty excited" about this study, says evolutionary geneticist Daniel Promislow of the University of Georgia. The work means that bacteria may be "central for understanding the genetics of aging," he says, and that "we need to think about the consequences of getting rid of bacteria we actually want in our body."

Related sites
Seymour Benzer's lab home page
Background on the genetics of aging from the University of British Columbia