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http://www.sciencedaily.com/releases/2010/09/100901132157.htm

ScienceDaily (Sep. 1, 2010) — Researchers at Boston University and the Wyss Institute for Biologically Inspired Engineering at Harvard have discovered that charitable behavior exists in one of the most microscopic forms of life -- bacteria. Their findings appear in the Sept. 2 issue of Nature.

In studying the development of antibiotic-resistant strains of bacteria, the researchers found that the populations most adept at withstanding doses of antibiotics are those in which a few highly resistant isolates sacrifice their own well being to improve the group's overall chance of survival.

This bacterial altruism results when the most resistant isolates produce a small molecule called indole.

Indole acts as something of a steroid, helping the strain's more vulnerable members bulk up enough to fight off the antibiotic onslaught. But while indole may save the group, its production takes a toll on the fitness level of the individual isolates that produce it.

"We weren't expecting to find this," said lead investigator James J. Collins, Ph.D., professor of Biomedical Engineering at Boston University and a core faculty member of the Wyss Institute. "Typically, you would expect only the resistant strains to survive, with the susceptible ones dying off in the face of antibiotic stress. We were quite surprised to find the weak strains not only surviving, but thriving."

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