Bacteria can change into more infectious and deadly organisms after a stint in space, a new experiment suggests.
A science experiment on board space shuttle Atlantis in 2006 included Salmonella typhimurium bacteria, which is often fatal in humans.
When the bacteria—which had been safely isolated from the space crew—returned to Earth, scientists injected them into mice.
They found the space-faring bacteria caused death quicker and more often than Earth-restricted organisms.
The findings are concerning for future astronauts who will embark on longer space missions farther away from Earth-based medical help, experts say.
Genetic Transformations
Cheryl Nickerson is an associate professor of microbiology at Arizona State University's Biodesign Institute and lead author of the study.
Nickerson wanted to see if space's low-gravity environment would affect Salmonella. Usually a culprit in food poisoning, the bacteria can cause vomiting, fever, diarrhea, and abdominal cramps. Most types of Salmonella, which can grow on most foods, are fatal in the elderly or young if left untreated.
When the bacteria returned to Earth, genetic sequencing showed that 167 genes and 73 proteins had been altered.
One protein, called Hfq, helped control more than a third of the altered genes. Hfq regulates RNA—the code of bacterial life—during stressful events. When activated, the protein previously had been shown to strengthen several types of pathogens.
An technique called scanning electron microscopy also showed some Salmonella were starting to form biofilms, a protective slime layer.
On Earth, biofilms can grow on ship hulls and clog pipes, costing industry billions of dollars. Biofilms also worsen some diseases and reduce the effectiveness of many antibiotics.
Nickerson and colleagues, whose study appears online in today's Proceedings of the National Academies of Sciences, have tested bacteria in a variety of harsh environments.
"In the last few decades, huge leaps of knowledge have been made when we test biology in extremes," she said.
"Situations where it is very hot, very acidic, or low oxygen have taught us an enormous amount about how cells respond to those environments, and from that we've made huge advances in biotech and bioengineering."
All About the Fluids
It's not lower gravity that makes bacteria deadlier in space.
The key environmental change is a mechanical force known as fluid shear, or the motion of fluid around a cell.
In human gastrointestinal tracts, this current slows down or even stops, creating an area of low fluid shear. These environments allow bacterial infections to flourish. Space is also a low-shear environment.
"Fluid shear ... is an environmental signal that had been overlooked for quite a while," Nickerson said.
That's because ground-based techniques can't replicate accurate fluid shear environments.
But in space, scientists can control fluid shear far better than in any Earth-based lab.
Deep Impact
By understanding the role of fluid shear on the evolution of disease-causing bacteria, scientists hope to offer better techniques to fight disease on Earth.
David Niesel, chair of microbiology and immunology at the University of Texas at Galveston, was not involved in the study.
"[The study] is a nice piece of work. It shows an increase in virulence in an animal model and a molecular mechanism that could account for that," he said.
"Anything we learn about how bacteria respond to new environments and their virulence mechanisms may help us understand how these organisms cause disease, and that gives us new opportunities to come up with therapeutics to combat disease on Earth."
Understanding how bacteria alter themselves in space will be especially important for future long-term missions, such as colonization of the Moon or a manned mission to Mars.
"What happens in microgravity at the cellular level is not really well understood," said Steve Maclean, a Canadian astronaut and crew member on the 2006 Atlantis shuttle that housed the experiment.
Since bacteria are always present inside humans, it is impossible to prevent any of the organisms from getting into the space shuttle.
"Given that bacteria survive better and our immune system is functioning at a lower level, does this increase your risk of infection?" Maclean said.
"It's something to think about before we go to Mars."
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