Space bugs: Astronaut Heide Stefanyshyn-Piper activates growth of a sealed sample of Salmonella bacteria aboard the space shuttle Atlantis last September.
Credit: NASA
SYDNEY: Space flight has been shown to change the way disease bacteria behave, making them much more virulent. This has worrying implications for astronauts whose immune systems are already weakened in space.
In news which could have astronauts tanking up on antibiotics, experts found that Salmonella typhimurium bacteria had altered patterns of gene expression and were more than three times as likely to kill mice after 12 days orbiting Earth in the payload of the NASA shuttle Atlantis.
"Human presence in space, whether permanent or transient, will be accompanied by the presence of microbes," said astrobiologist Cheryl Nickerson, of the University of Arizona in Tempe, USA. Yet before now, she said, the effect of spaceflight on the disease risk posed by microbes was a mystery.
Simulated microgravity tests
Nickerson is co-author of a study detailing the research in today's edition of the U.S. journal Proceedings of the National Academy of Sciences.
Prior to the present study, her team had already built up a large body of data using simulated microgravity on Earth, which revealed changes in colonies of Salmonella. "Since the virulence of the pathogen and the status of the immune system are two key factors that determine the outcome of an infection, it seemed only logical to [go on to] look at the ability of true space flight to alter microbial virulence," Nickerson said.
To this end, the researchers compared two cultures of Salmonella: one aboard the U.S. space agency's Atlantis for a 12-day mission in orbit during September 2006, and another back on Earth in a laboratory specially controlled to duplicate temperature, humidity and other growth conditions on the shuttle.
After the flight, some of the bacteria in both groups were analysed for gene and protein changes. Compared to bacteria that remained on Earth, the space-faring Salmonella showed altered expression of 167 genes - many with some link to a protein called Hfq.
Bacteria on board the shuttle were also prone to clump together and collect into protective bio-films.
Further studies showed that the microbes taken for a space ride killed up to 40 per cent of laboratory mice that ingested them, compared to just 10 per cent of the mice that ingested samples of the Earth-bound bacteria.
Bio-films and virulence
The researchers are at a loss to fully explain the increased deadliness as yet, but suggest that the formation of biofilms in microgravity could have a role. The relatively smooth and 'non-turbulent' environment of zero-gravity might also have an effect on how the bacteria behave, they said.
Roberto Anitori, a microbial ecologist from the Australian Centre for Astrobiology at Macquarie University, in Sydney, commented that the study is an important contribution to a field in which very little is known. "If this turns out to be true for other pathogens, it will open a Pandora's box. I think this could be quite a concern for NASA," he said.
Astronomer Chandra Wickramasinghe, who heads the Cardiff University Centre for Astrobiology in Wales, said the research might have more far-reaching consequences. He believes the finding backs up his own theory that life on Earth is derived from comets or dust that seeded space-travelling microbes into the atmosphere. "The increased virulence as well as clumping and growth characteristics discovered by the authors could be an indication that bacteria are evolved to be space travellers," said Wickramasinghe.
Whether or not that turns out to be true, the results will be useful for minimising the risk of disease to astronauts on future Moon or Mars missions, as well as potentially aiding the fight against increasingly antibiotic-resistant strains of Salmonella here on Earth.
