Actually living on Mars might be one of the only ways to successfully live without any microbes, because a huge part of the gut microbiota is needed to train yo

Actually living on Mars might be one of the only ways to successfully live without any microbes, because a huge part of the gut microbiota is needed to train your immune responses to other microbes. But if there are no other microbes around you'd be ok for a while, but would probably develop autoimmunity or have other immune problems eventually. People with SCID have to live in a filtered air bubble (https://en.wikipedia.org/wiki/Severe_combined_immunodeficiency https://en.wikipedia.org/wiki/Severe_combined_immunodeficien...) so it's possible, but if I remember correctly there are side effects. Mars is kind of a similar lifeless bubble though.