Universe Today
Hopefully, we’re about to travel back to the Moon relatively soon. And while the original “giant leap for mankind” was taken by a human, Neil Armstrong brought a plethora of other forms of life along with him. Humans themselves are essentially walking ecosystems, and understanding how our microbial companions survive in the harsh environments of space will be critical to ensure the health and safety of future astronauts, no matter where their giant leaps might be. A new PhD thesis from Tommaso Zaccaria at Radboud University showcases just how well-suited to some of these harsh environments terrestrial pathogens actually are.
The thesis can be thought of as being split into three sections. In the first, Zaccaria subjected four well known pathogens from Earth (including the one that causes pneumonia) to simulated Martian conditions. These included extremely low pressure, dessication, high UV radiation, and exposure to high-concentration brines with perchlorate in it. As with many of these experiments, the headlines are that the microbes survived particularly well, with some strains surviving up to 16 days of desiccation. This is what normally hits the headlines of articles about these types of experiments.
Dig into the data, however, and the actual picture is much more bleak for the bacteria. Mars isn’t a one-off environmental condition. It combines some of the deadliest known things life can be subjected to - lack of water, high UV radiation, low atmospheric pressure, and perchlorates themselves all combine to make the Martian environment much more deadly than any one condition would be on its own. In the thesis, the survival of the bacteria drops from 16 days to one.
Fraser interviews Dr. Corine Bakermans about Mars’ various defense mechanisms against Earth life.Interestingly, there is one aspect of Mars' environment that seemed to help the bacteria’s survival rate - regolith. Zaccaria suggests that its jagged surfaces offer a place for water to hide, and offer microbes some protection from the unforgiving UV radiation. But it also houses the toxic perchlorates, making such survivability a trade-off in the long run.
Another critical feature is that the physical changes some of these bacteria went through in order to adapt to the harsh environment made them almost invisible to human immune systems. In fact, they physically shrank in some cases, and when Zaccaria introduced them to peripheral blood mononuclear cells (PMBCs), a type of human immune cell, the cells produced fewer cytokines and reactive oxygen species, both weapons they use to destroy invaders. In other words, bacteria that can survive on the Martian surface might be even more pathogenic to astronauts due to the physiological changes they undergo to live there.
The second part of the thesis focused on the damage that regolith—and lunar dust—can do to astronauts themselves. To test this, he subjected in vitro human epithelial cells (i.e., those that line a person’s airway) and living mice to both Lunar Mare Simulant and Martian Global Simulant. Unsurprisingly, inhaling this dust was a distressing experience for both the human cells and the mice. While Apollo astronauts complained of “lunar hay fever,” Zaccaria inventories the specific reactions these cells had: local tissue inflammation, neutrophilia (i.e., an increase in white blood cell activity due to damaged tissue), and increased activity in genes that control mucus production and lung fibroids—both precursors to chronic respiratory disease. Notably, the lunar dust simulant was even more damaging than the Martian simulant laced with perchlorates.
Fraser explains a technology to use an electric field to clean off Moon dust.The third part of the thesis focused on validating the planetary protection protocols we use when we send robotic probes to other worlds. In these experiments, Zaccaria evaluated the extremes that eukaryotes can survive on the way to a moon of Jupiter or Saturn. He noted that yeasts actually have some of the highest survival rates of any microbes. After running some transcriptomic analysis of why, he realized that some of the microbes, such as R. frigidalcoholis, intentionally stall their own growth cycle in order to focus on DNA repair.
However, the same argument goes for these experiments - the environmental conditions were introduced in series rather than in parallel, so it’s not necessarily a good indication of what type of environment the microbes would be subjected to in space. That being said, our own planetary protection protocols are also run in series, so the argument that we need to make sure we design them to account for all the possible microbes (including yeasts) that could survive the current protocols is completely valid.
As we expand out into space, we’re going to need a better understanding of our biological companions - whether wanted or unwanted - and how they survive these conditions. Work like this thesis is how we can go about doing that, and as we collect more information about how strains react to the different environments they’ll be subjected to throughout the solar system, the more we learn about the limits of life here on our own planet.
Learn More:
Radboud University Medical Center - Pathogens survive conditions on extraterrestrial locations
T. Zaccaria - Life beyond earth: microbial survival and immune health in space
UT - Some Extremophiles Could Survive an Asteroid Impact on Mars, and the Dangerous Journey to Earth
