Microbe exhibits out-of-body activity

From Seattle, at the American Association for the Advancement of Science Annual Meeting

INDEPENDENT LIVING. Anthrax bacteria, shown here as chains of cells being released from an immune cell, may sometimes reproduce in soil instead of staying dormant as spores. Hanna

Scientists studying infectious microorganisms have tended to focus on human and veterinary diseases. But now microbiologists are finding that such microbes may have compelling lives on their own.

Consider anthrax, which is naturally present in soil and can reproduce rapidly after a cow, sheep, deer, or bison—and occasionally someone who works with these animals—takes up spores. “According to current dogma, the anthrax spore is totally dormant when outside of a person or animal,” says Philip C. Hanna of the University of Michigan Medical School in Ann Arbor. But Hanna now reports evidence suggesting that the bacterium can also undergo its entire life cycle in soil.

When he placed anthrax spores in a broth made from sterilized but nutrient-rich soil, Hanna observed a small amount of germination, bacterial reproduction, and formation of new spores. When conditions in soil become “just right,” he suggests, “a complete life cycle is possible and, I believe, probable.” However, he cautions, competition from other microbes might limit the proliferation of free-living anthrax.

If an anthrax cell does reproduce in soil, it might exchange genes with related bacteria, making its continued evolutionary development difficult for scientists to predict. Moreover, the new anthrax finding “bodes very poorly on any potential ambitions for eradicating its spores from the environment,” Hanna says.

Hanna emphasizes that anthrax in nature isn’t a threat to public health. For instance, the bacterium doesn’t spread from one person to another. To initiate serious illness, weapons developers have had to grow the microbe in a lab and then refine and process the spores into a form that is easily deployable, remains suspended in air for extended periods, and penetrates deeply into lungs.