Due to its oxygen-free atmosphere, radiation exposure and lack of nutrients, Mars is a hostile place for human life. However, it may not be so unfriendly to the microbes we bring with us – including some that we would actually rather not flourish too much.
Three years ago, astrobiologists noted the presence of sugar in meteorites and revealed that some bacteria would grow when fed a space candy diet. That’s probably not a problem, because other conditions would likely prevent microorganisms from making themselves at home at future asteroid bases. The same might not be true on Mars, so a team led by German Aerospace Venter PhD student Tommaso Zaccaria decided to see how some local microbes would behave in a simulated Martian environment. Pretty good, as it turns out, maybe too good.
One thing we know about missions to other worlds is that we bring hitchhikers. Even the best attempts to disinfect spacecraft fall short, as the persistence of bacteria outside the ISS proves. When people are involved, the process of keeping everything clean becomes an order of magnitude more difficult.
We depend on beneficial bacteria, especially in our gut, so some of these cosmic travelers will be welcome. Others should be fairly neutral, unless Mars turns out to have a life of its own that can’t handle what we bring. However, future astronauts would prefer to avoid cases of sepsis or dysentery caused by unwanted companions from home.
The authors posted four examples of bacteria (Burkholderia cepacia, Klebsiella pneumoniae, Pseudomonas aeruginosa, And Serratia marcescens) in media with exposure to air, soil chemistry, and UV radiation, such as those our rovers encountered.
The responses of the bacterial species varied. For example, B. Cepacian apparently they cannot grow in the presence of sodium perchlorate – common in brines on Mars – unless they are fed glucose. On the other hand, sodium perchlorate doesn’t seem to be affected K. pneumonia. Repeated dehydration to simulate the typical lack of water on Mars reduced the number of species quite sharply. Nevertheless, all four species survived (at least to some extent) for days or weeks, and fared better when fed imitation Martian regolith (soil) than just sugar.
The ultimate test was the response to a series of conditions on Mars: dealing with the light, the soil, the air and the water at the same time. S. marcescens in particular, he seems ready for whatever Mars throws at him, even if encountered at the same time – and that’s even without time for evolution to do its work. Commonly seen in hospital-acquired infections, S. marcescens is known for urinary tract infections and septic wounds.
“At first we thought that the regolith would have a toxic effect on the cells and therefore limit their growth,” Zaccaria told Sciencenews. “But instead we saw it was the opposite.” The authors suspect this is because the soil particles provide a place to hide from UV light and other threats to bacterial survival.
When (not if) pathogens accompany humans to Mars in our guts or on our skin, some can be expected to end up in the soil around the base. This work suggests that they can grow when given access to water, no matter how salty. Without a healthy ecosystem to keep them in check, the danger of these pathogens infecting other astronauts is high, which is a major concern for someone who is further from the nearest hospital than any human has ever been.
The finding was not entirely surprising. A 2022 study found that a type of yeast could survive in Mars’ salty water on the rare occasions it freezes. It has also been determined that several extremophiles are likely to flourish on Mars. But the fact that these four types are not only likely to accompany humans, but could also be a serious problem for us once they get there, makes the implications much more serious.
The results have been published in the journal Astrobiology.