A year in space is not any move into the park. Just ask Scott Kelly, the American astronaut who spent a year on the International artificial satellite (ISS) in 2015.
His long-term stay in space changed his DNA, telomeres, and gut microbiome, he lost bone density, and he still had sore feet three months later.
But it is a whole other thing to survive within the naked space outside the protection of the ISS, where UV radiation, vacuum, huge temperature fluctuations, and microgravity are all imminent threats.
So, it's quite a feat that a species of bacterium first found in a very can of meat, Deinococcus radiodurans, was still alive and kicking after a year spent living on a specially designed platform outside the pressurized module of the ISS.
Researchers are investigating these mighty microbes for a while; back in 2015, a world team founded the Tanpopo mission on the skin of the Japanese Experimental Module Kibo, to place hardy bacterial species to the test.
Now, D. radiodurans has passed with success.
The bacterial cells were dehydrated, shipped to the ISS, and placed within the Exposed Facility, a platform continuously exposed to the space environment; during this case, the cells were behind a glass window that blocked out UV light at wavelengths not up to 190 nanometres.
"Results presented during this study may increase awareness regarding planetary protection concerns on, for example, the Martian atmosphere which absorbs UV radiation below 190-200 nm," the team from Austria, Japan, and Germany wrote in their new paper.
"To mimic this condition, our experimental setup on the ISS included a silicon oxide glass window."
This isn't the longest time D. radiodurans have been kept in these conditions – back in August we wrote a few samples of the bacterium being left up there for 3 whole years.
But the team wasn't trying for a record, instead, they were trying to uncover what makes D. radiodurans with great care good at surviving in these extreme conditions.
SEM images of D. radiodurans control (left), and after LEO exposure (right). (Ott et al., Microbiome, 2020)
So, after a year of radiation, freezing and boiling temperatures, and no gravity, the researchers got the spacefaring bacteria to backpedal to Earth, rehydrated both an impression that had spent the year on Earth and also the Low Earth Orbit (LEO) sample, and compared their results.
The survival rate was lots lower for the LEO bacteria compared to the control version, but the bacteria that did survive looked as if it would be doing okay, whether or not they'd turned a touch different to their Earth-bound brethren.
The team found that the LEO bacteria were covered with small bumps or vesicles on the surface, a variety of repair mechanisms had been triggered, and a few proteins and mRNAs had become more abundant.
The team isn't exactly sure why the vesicles (which you'll be able to see within the picture above) formed, but they are doing have a pair of ideas.
"Intensified vesiculation after recovery from LEO exposure can function a fast stress response, which augments cell survival by withdrawing stress products," the team wrote.
"Additionally, outer membrane vesicles may contain proteins important for nutrient acquisition, DNA transfer, transport of poisons and quorum sensing molecules, eliciting the activation of resistance mechanisms after space exposure."
This kind of study helps us understand whether bacteria could survive other worlds, and perhaps even the journey between them, which can become more and more important as we humans and also the germs we bring with us begin to travel farther than our Moon into the system, and in some unspecified time in the future maybe even beyond.
"These investigations help us to grasp the mechanisms and processes through which life can exist beyond Earth, expanding our knowledge on the way to survive and adapt within the hostile environment of space," said the University of Vienna biochemist Tetyana Milojevic.
"The results suggest that survival of D. radiodurans in LEO for an extended period is feasible thanks to its efficient molecular response system and indicate that even longer, farther journeys are achievable for organisms with such capabilities."
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