What existing life on Earth is best suited for the Martian environment?

Question

What existing life on Earth is best suited for the Martian environment? By best suited, I mean it could theoretically be placed on Mars and easily adapt or thrive within the existing environment the planet has to offer.

I know from my own research that extremophiles are potential candidates. There is a discussion about Could any life from Earth survive in Enceladus' oceans? which is relevant to my question, however this focuses on bacteria found in water only. There is a question on Is it possible to grow plants on Mars? which is related, however not exactly the same, and from the information that the answer contains leads me to believe that plants would not be good candidates for my question. There is also a discussion which relates to the search for life on Mars and how we could contaminate it with human boots on the ground.

Answer 1

There is a chamber at the German Aerospace Center designed to imitate the Martian environment. So far there are two published experiments showing that some organisms could survive in the chamber. An imitation of Martian regolith was used, and the organisms were exposed to an imitation of Martian atmosphere with the pressure, temperature range, moisture fluctuations, and solar radiation exposure of Mars.

In the first test, alpine and polar lichens managed to increase levels of photosynthesis over the course of 34 days in this environment - when they had only a reduced radiation dose to deal with similar to that found in cracks and recesses in the regolith. Samples exposed to full radiation doses simply managed to survive. Some cyanobacteria also survived.

In the second test, a species of black yeast recovered from an initial dive in metabolic activity after the first day of exposure, to normal levels after a full week. A second fungus, a microcolonial variety, survived but was struggling.

Note: The test chamber doesn't imitate Martian gravity or the cosmic radiation that would be experienced on the Martian surface. Possibly that skews results.

Answer 2

Humans. We have technologies to survive on Mars, and even inside Enceladus. Life doesn't only adapt itself to the environment, life also adapts the environment to its need. Spacesuits and constructions are just a part of what life does to stay alive. It is not only up to the nanoengineering of the microbes in our body, our brain is an emergent phenomena on top of that which helps the seemingly unstoppable process of creating survivability.