To better understand the role of bacteria in health and disease, National Institutes of Health researchers administered viruses to fruit flies and monitored the lifetime activity of hundreds of genes that scientists traditionally thought control aging. To their surprise, they not only extended the lives of flies, but also drastically altered the activity of many of these genes. Their results reveal that only about 30% of genes are traditionally associated with aging determining an animal's internal clock, while the others are affected by the body's response to bacteria.