Imagine that you are in a space craft orbiting the earth. You are cruising through space only to realize that you are not alone. There is an intruder on board, an unknown life form. Science fiction, right? Not exactly.
In mid-March of this year, NASA researchers announced that they had found an unknown life-form aboard the International Space Station. The interstellar hitchhiker was a bacteria whose genome, at that time, was unknown to science. OK, reality time. The bacteria wasn’t from some far off planet in another galaxy, it was from good-old-earth, a bacteria from the Methylobacterium genus, a group of bacteria that primarily live on plant roots. The astronauts had swabbed down the inside of the international space station and lo and behold, when the swabs were sent back to earth and the genetic material sequenced, they had identified an entirely new bacterial genome from within this genus. It was not the first. The first was identified in 2017, again aboard the International Space Station. These microbes probably didn’t evolve in space, there hasn’t been enough time for that, but rather hitched a ride aboard the Station as stowaways. Once there they liked the conditions so much, they set up shop and stayed. The environment aboard the International Space Station is not for the faint of heart. For one, there is, of course, no gravity. It's pretty tough for a bacteria to colonize a surface, say the wall of the Space Station, when there is no gravity holding it there. Furthermore, levels of radiation are higher than normally found on earth, and there is little to eat, even when you are the size of a microbe. Yet clearly, these little interlopers have figured out a way to survive in this very hostile environment. These new bacteria are certainly not the only ones aboard the International Space Station. The microbial community aboard ship looks, for the most part, like the microbes that live on and within us, our microbiome. In recent years, the importance of the microbiome has become established, as they help us with digestion, regulate our immune systems and help to produce vitamins. And, for the most part, the community of microbes in the International Space Station effectively mirrors our microbiome, so much so, that every time a new human passenger arrives or departs from the station the community aboard ship changes accordingly, more closely resembling the microbiome of the current inhabitants on board. Now we are finding that there are also bacteria that have hitched a space ride with us, that are not part of our microbiome. What special attributes of these bacteria allow them to be successful in space, while remaining obscure on earth? Why them and not some other species? It is a puzzle. Colonization of Mars will not be just a human endeavor, but will be a microbial adventure as well. Most of the microbes will be familiar to us and members of our microbiome. Others will be much less familiar and perhaps anonymous. They willl be of earth origin but strangers to us, as was true for the interlopers found on the Space Station. When we reach Mars, bacteria will be right along side. The vast majority will find the environment too hostile and will die. Some, however, may survive. As the fictitious character, Dr. Ian Malcolm, from the movie Jurassic Park remarked, “Life finds a way.” We now know that may include bacterial life finding a way, through us and our space craft, to colonize foreign planets, includng Mars.