Can terrestrial microbes survive in outer space — and if so, how do they do it? These are some of the questions that researchers at City of Hope, working with NASA’s Jet Propulsion Laboratory, set out to answer. Their discoveries are shedding new light on a range of subjects from human health to the origins of life on Earth.
The study, part of a long-term collaboration with NASA, was led by City of Hope graduate student Abby Chiang, Ph.D., under the supervision of Markus Kalkum, Ph.D., professor and director of the Mass Spectrometry and Proteomics Core at Beckman Research Institute of City of Hope. Chiang was awarded her doctorate in part as a result of this work, and the results were published in June by the American Society for Microbiology.
Bacteria Travel Into Space
The idea for this project began when JPL’s Kasthuri Venkateswaran found that certain strains of bacteria, including Bacillus pumilus and Bacillus horneckiae, were especially hardy. They were isolated in cleanrooms where spacecraft are built, and were also found to survive when exposed to the environment outside of the International Space Station. The spores of these hardy microbes were also found to withstand treatment with peroxide and ultraviolet rays.
“If future space missions ever try to look for life on other planets, the spacecraft doing the searching have to be very clean. We don’t want to go to other planets and look for life only to find that we brought it with us,” said Kalkum.
To study what happens to microbes in space, Bacillus pumilus spores were placed in a special container on the outside of the International Space Station (ISS) and kept there for 18 months.
“The conditions were quite extreme — microgravity, the vacuum of space, exposure to UV and UVC rays, cosmic radiation and particle radiation,” said Chiang. “And when the spores were brought back to Earth, some of them were very much alive.”
How did the spores survive such exposure?
Chiang and Kalkum used mass spectrometry, which analyzes the structure of molecular compounds, and proteomics, a method of studying proteins — the same techniques that are being used to study the biological mechanisms in cancer. And they made some fascinating discoveries. The metabolism of the spores had greatly slowed down, the protein coat that protects them was bigger and they had stronger virulence factors. No relevant changes to their DNA were found, which meant that the changes were most likely not genetic mutations.
This new information could now help inform the development of a more effective method of cleaning space hardware. Keeping an eye on what microbes are on the space station and learning how they adapt in microgravity continues to help us understand how best to protect astronaut health.
But the experiment has other important implications as well. By understanding the mechanisms by which bacteria protect themselves and grow stronger, we can also learn how to strengthen “good” bacteria, the probiotics that play such an important role in health.
In fact, Chiang and Kalkum also worked on a National Cancer Institute-funded study of the probiotic Lactobacillus reuteri, a strain of bacteria that inhibits gut inflammation, which when chronic can lead to colon cancer.
“Probiotic bacteria can be flimsy,” said Kalkum. “But if you can make them more hardy by learning the mechanisms they need to resist extreme environment, you could engineer them to live better inside humans in a way that is beneficial to the humans as well.”
If NASA wants to send astronauts to explore the moon and Mars, this type of research would be essential.
Meanwhile, Inside the Space Station …
Bacteria aren’t the only microbes of concern on the ISS. Several types of fungi have been discovered living inside it, particularly on wet surfaces. In an earlier City of Hope/NASA collaboration, Chiang and Kalkum found that, like the bacteria, the fungi had more robust growth than their counterparts on Earth.
One strain of fungus found on the ISS, Aspergillus fumigatis, is an opportunistic pathogen, and life aboard the space station made it even more virulent than its clinical counterpart CEA10, a type of Aspergillus sometimes found in hospitals that can cause illness in immunosuppressed patients.
The adaptive mechanism that strengthened it, however, was exactly the opposite of what happened to the bacteria. Where bacteria reduce their energy consumption and slow their metabolism, fungi in space speed up their metabolism. Some fungal species also produce a protective coating of melanin — as if they were making their own sunscreen.
Understanding these mechanisms is crucial if we are to eliminate them in clinical settings, as well as in space, where they could be harmful to astronauts on long-term missions, and even simply to do good science as robotic explorers study extraterrestrial bodies.
However, other fungi found growing on the space station, like Penicillium, are our allies.
“Some of these fungi can produce useful things, like antibiotics for treating diseases,” Kalkum said “So on the space station they could actually use these as chemical machines to produce useful compounds during space travel.”
The Origins of Life on Earth
“Are you familiar with the panspermia hypothesis?” Kalkum asked.
Panspermia is a Greek word that means "seeds everywhere,” and this theory posits that seeds, or microscopic organisms, traveling through space might have carried these seeds to Earth and been the origin of life here.
“In the early days of the solar system, there was much more activity with meteoroids and asteroids, and if some microorganisms or biosignatures might have been able to survive space travel long enough, it could have been the way that life was brought to Earth,” said Kalkum. “We don't have evidence, but this study raises the possibility because some of these organisms are very hardy and resistant to extreme conditions.”
What began as a graduate student project for Chiang is not only helping us understand how microbes survive in space, it may be one small but important step toward finding an answer to an age-old question: Is there life elsewhere in the universe?
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