Astronauts are usually kept in quarantine before flight to prevent them from coming into contact with germs that they might bring on board a spacecraft. But last year, bacteria didn't have to sneak onto space shuttle Atlantis. Scientists put the bacteria on board, safely sealed up in tubes, and watched them blast off.
The mission involved a study lead by Arizona State University biologist Cheryl Nickerson that shows spaceflight affects the strength of salmonella, a germ that causes diarrhea and food poisoning.
"Most of us have experienced a salmonella food borne infection, and it's not pleasant," Nickerson says.
While the shuttle orbited Earth, one of the astronauts turned a crank on a special canister. This mixed the bacteria with some food so that they started to grow. Then the shuttle headed home.
"These samples were recovered incredibly quickly off of the shuttle upon landing," Nickerson says.
Stronger, Faster Bacteria
Within a couple of hours, before the bacteria could readjust to life on Earth, the scientists used them to infect mice. These mice ended up doing much worse than animals infected with bacteria grown on earth.
"They got sick quicker and they ultimately succumbed to the infection quicker," Nickerson says.
This is the first time anyone has shown that bacteria can become more dangerous after spaceflight, Nickerson says. Previous studies had shown that some bacteria grow faster in space, or seem better able to resist antibiotics.
"So we had a lot of basic fundamental knowledge that spaceflight can change a lot of properties of microbial cells, but we didn't have any mechanistic understanding at the molecular level of why that was happening," Nickerson says.
To answer the why question, researchers looked for genetic changes in the salmonella grown in space. Overall, they found changes in the activity of more than 150 genes.
Nickerson says many people find it surprising that weightlessness has an effect on microbes.
"Why would you expect that microgravity would be an environment that cells would respond to?" Nickerson says.
She says she believes that the bacteria are actually reacting to the way that low gravity changes how fluid pushes against their cell membranes.
"I'm kind of giving them human properties here, but they know when that force is low and they know when that force is high," she says.
Astronauts Face Double Threat
The increased virulence of salmonella intrigues researchers who study how spaceflight affects the health of astronauts.
Millie Hughes-Fulford works at the VA Medical Center in San Francisco. More than a decade ago, she went up on the shuttle to do experiments. Like all astronauts, she was put in strict quarantine before flying.
"You can't go into a drugstore and buy a pack of gum. In training, only certain people can come near you and those people have been certified to be healthy," Hughes-Fulford says.
But astronauts do sometimes get sick in space. Hughes-Fulford's work suggests that low gravity can weaken people's immune system. She says certain immune cells just do not act normally in space.
"They can't just turn on like they normally do when they're presented with a challenge," Hughes-Fulford says.
So, she adds, the new bacteria study suggests astronauts could face a double threat to their health in space — a weaker immune system trying to fight off stronger bacteria.
The study is being published today in the Proceedings of the National Academy of Sciences.
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