In 2006, NASA grew Salmonella in space; the bacteria returned more virulent than genetically identical germs cultivated on Earth

What doesn't kill you makes you stronger. This apparently holds for bacteria, too, and that should worry you a little. In September 2006, NASA launched not astronauts but vials of Salmonella into space aboard the Space Shuttle Atlantis as part of the STS-115 mission, a flight that carried the shuttle crew to the International Space Station to deliver and install a new truss segment, with the bacteria riding along as a dedicated shuttle-based experiment rather than a station laboratory project. Of course, not as contaminants or by mistake, but as an on purpose mission.

Eleven days later, it returned to Earth, but it did not return as it was. According to a peer-reviewed PNAS article titled “Space flight alters bacterial gene expression and virulence and reveals a role for global regulator Hfq” in 2007, the space-bred Salmonella were tougher and more aggressive, modifying the expression of 167 of its genes and thereby making it more dangerous to mice.

The experiment that should've received more hype


Cheryl Nickerson of Arizona State University’s Biodesign Institute and her microbiology team embarked on a mission to investigate whether real spaceflight alters the virulence level of pathogens in ways that lab simulations cannot. NASA sent identical samples of Salmonella typhimurium, one of the most common pathogens causing food poisoning in the United States, into space for cultivation, while another batch of the same was cultivated back on Earth under similar conditions, except gravity.

Genetic and proteomic analyses revealed many changes in the bacteria that had been sent to space. Moreover, it appeared that a regulatory protein, which acts like the pathogen’s internal control switch and goes by the name Hfq, plays a key role in bringing about the changes. In the experiments involving mice, the space-flying strain proved to be three times more dangerous in infecting the subjects than its identical Earth-bred counterpart. It was the same strain of the same organism, but different gravity resulted in a different genetic configuration.

Why your gut and the space station have more in common than you'd think

This is the part where we get answers to the "why," and surprisingly it's quite relatable. Nickerson et al. hypothesize that fluid shear, which in this case refers to the strength of force exerted on the surface of bacteria by liquid that surrounds them, drops sharply in microgravity. The low-shear environment of space is similar to that of our digestive system, which means that the physiological resemblance between the two environments, not the mission itself, was the unplanned part; space unintentionally mimicked the conditions the bacteria "expect" to find once inside a human body.

This physiological coincidence turned the low-shear conditions of orbit into an unexpected research tool for studying a disease-causing pathogen that affects roughly 1.35 million people in the US each year, according to CDC estimates. That didn't go unnoticed by NASA either. In its published countdown of top research results from the International Space Station program, NASA credited the Salmonella and Hfq findings as one of the station program's most notable discoveries, particularly stressing that the ability of ordinary pathogens to make us sick increases in spaceflight, though this environment can be somehow controlled.

The reconfirmation mission and ongoing research

It seems to be nothing more than the plot line of a low-budget science fiction thriller, but the follow-through has been anything but thrilling; it has been systematic. To prove that their 2006 findings were no accident, the same researchers performed another experiment on a later shuttle flight, Space Shuttle Endeavour's STS-123, in March 2008.

This follow-up was recorded by Arizona State University during that time. The second test flight was conducted to see if changing mineral content in the growth medium would help neutralize the increase in virulence, while other tests were being done to study the effects of spaceflight on various other infectious agents.

Why does it matter

This research is not just about astronauts eating contaminated chicken 250 miles above Ohio; it is about using the hostile environment to find out why the bacteria that are causing harm down here are becoming even more harmful than they already are. The understanding of the mechanisms that turn virulent genes of the bacteria on will be used to develop an effective vaccine or treatment of this infection, which we all experienced or knew someone who did. This research does not involve flags on the Moon or the landing on Mars but growing bacteria in a test tube, comparing it to the identical one from Earth and realizing that space could alter not only astronauts but their pathogens as well.