Microbes

Microbes are microscopic organisms. On Earth microbes live almost everywhere: in soil, in water, even inside animals. On Mars there are no known microbes.

Future settlers will bring microbes from Earth to Mars. They will live inside greenhouses, humans, and animals. Microbes are essential for many atmospheric processes, including the Nitrogen Cycle.

Microbes can be used in biotechnological factories to produce chemical substances, for instance, proteins. Additionally, there are thoughts about using microbes for terraforming.

Possible Martian microbes

The Martian surface is utterly sterile due to radiation and the absence of liquid water. The environmental conditions seem not to allow them to survive. Subsurface environments, however, may be favorable to microscopic life.

There are speculations about a threat towards the settlers or even towards Earth in case of return missions. And there are strong arguments against a threat. Microbes are always adapted closely to their natural host. In rare cases a microbe manages to jump from one terrestrial species to another. But this is rare. And this applies only for microbes that are already accustomed to live in hosts. The terrestrial soil microbes never jump to an animal, because they have adapted to the soil environment, and their whole metabolism depends upon this environment. With Martian microbes a jump is even more unlikely.

Furthermore, some people want to protect a possible indigenous Martian sub-surface biosphere from contamination by terrestrial microbes, which can only be avoided with an effort.

An answer from an epxert! Thanks for contributing.