Deadly bacteria that have spent time in space are already on Earthbut instead of killing humans, they might just save lives. Scientists are using bacteria cultivated on the International Space Station to help develop vaccines that experts say could revolutionize the medical field.

In 1998, researchers began studying how microbes such as bacteria, viruses, fungi, and yeast behaved in space because NASA wanted to be able to keep astronauts safe in the closed space station environment. What they found, specifically with certain types of bacteria, was surprising, says Tara Ruttley, NASA's associate program scientist for the International Space Station.

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"Bacteria can either respond in microgravity by sitting there and doing nothing, or they can become more aggressive and virulent," meaning they reproduce and evolve to cause disease more readily, she says. But that property of bacteria allows scientists to study exactly why certain bacteria, such as salmonella and MRSA, make people sick.

Scientists aren't exactly sure why certain bacteria become more virulent in space, but Ruttley says they believe it might be a stress response to being put into a low-gravity environment. But whatever the reason, studying bacteria that have spent time in space can make it easier for scientists to develop defenses.

"If you know the gene that makes bacteria more aggressive, you can build a defense against it," she says.

Last week, William Gerstenmaier, NASA's head of human explorations and operations, told the Senate Committee on Commerce, Science, and Transportation that medical discoveries and vaccines developed on the International Space Station could help the United States "create a new economy based on space-based research."

"It's like when we went to Africa to look for new plant species to use for drugs," he said. "We can create a new industry with this."

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Cheryl Nickerson and Roy Curtiss, professors at Arizona State University's Biodesign Institute, are leading the charge. They are studying salmonella that has spent time in space, in an attempt to "turn it from foe to friend" by crippling the disease-causing genes and replacing them with ones that protect against Streptococcus pneumoniae, the bacteria that causes meningitis, pneumonia, and many other diseases.

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Space: The New Frontier For Medical Breakthroughs