NASA wanted to conduct an experiment on how pathogenic
bacteria behaved outside the confines of Earth's gravity. Its experiment
bore some surprising
In September 2006, the Space Shuttle STS-115 launched, carrying in its cargo a
sample of Salmonella bacteria. The sample was part of a collaborative
experiment with Arizona State University's Center for Infectious Diseases and
Vaccinology, which wanted to investigate the effects of weightlessness and
other space phenomena on pathogens. ASU kept a separate sample in similar
condition on earth as a control group.
When the sample from space returned, they proceeded to feed both strains of
salmonella to lab mice.
The results were startling. After 25 days, 40 percent of the earth-strain
mice were still alive. Only 10 percent of the group infected with the
space-strain was still alive. Researchers conducted additional studies
which revealed that only 1/3 as many of the space-strain pathogens were needed
to kill a healthy mouse as earth strain pathogens. The conclusions--the
space strain had become far more deadly on its journey into orbit.
Genetic studies revealed that the bacteria had mutated quickly in space and had
a total of 167 genes changed.
Professor Cheryl Nickerson, one of the study's researchers cautions that the
cause for the increased toxicity is not definitively known (the 64 million
dollar question as she puts it), but she says that it is thought to be due to
fluid shear effects.
"Being cultured in microgravity means the force of the liquid passing over
the cells is low… [The cells] are responding not to microgravity, but
indirectly to microgravity in the low fluid shear effects."
"There are areas in the body which are low shear, such
as the gastrointestinal tract, where, obviously, salmonella finds itself,"
she went on to say. "So, it's clear this is an environment not just
relevant to space flight, but to conditions here on Earth, including in the
Nickerson sees the mutation as a natural adaptation to a
changing environment in order to survive. The increased toxicity is a
The research will be published in today's edition of “Proceedings of the National Academy of Sciences