Discovery of sulfide as an energy source for microbes that has potential for Mars

Researchers have discovered that sulfide is an energy source that works in the bitter cold of Canada and could help microorganisms to grow on Mars.

Simulating an ancient martian environment

In a paper published today (2 July 2020) in Scientific Reports, the research team led by Dr Michael Macey, a Research Associate in the OU’s Faculty of Science, Engineering, Technology and Mathematics, describes how fieldwork at Axel Heiberg Island in the Canadian High Arctic, which has an environment directly applicable to those in ancient Mars, revealed that the most abundant microbe was Halothiobacillus, which is known to use sulfide to generate energy.

Studying aqueous environments on Mars

The OU teamed up with researchers from the research group of Dr Clare Cousins from the University of St. Andrews and Dr Mark Fox-Powell, a Research Fellow at Astrobiology OU, the latter of which joined an expedition of researchers led by Professor Gordon Osinski from Western University (Ontario, Canada). The team visited the Colour Peak Springs on Axel Heiberg Island because the high salt concentration of these waters provided an ideal analogue environment to study aqueous environments on Mars (over 4 billion years ago), when the planet was rich in water. However, since then it has dried out, leaving places with much less water and high concentrations of salt during the transition - and no liquid water on the surface today.

Dr Fox-Powell said: “It really was the experience of a lifetime. Spring systems like this are very rare on Earth and seeing them up close helps put that into perspective. They don’t freeze even when the air temperature is below zero, so compared to the surrounding Arctic tundra, the springs can seem like an oasis. It’s easy to see how similar environments on Mars could have provided a habitat as the planet cooled.”

New method to extract DNA

The expedition delivered samples to the OU, and Dr Macey was able to extract the DNA and identify the microbes present. While extracting DNA from cells is a standard method, none of the existing protocols would allow the team to extract DNA from the low number of cells combined with the very concentrated salts in these samples. Ultimately, an intense dilution and filtering protocol developed for this study allowed the team to wash out the harsh chemicals and concentrate the cells. This led to the discovery that the most abundant microbe was Halothiobacillus, which is known to uses sulfide to generate energy.

Evidence to support new missions to Mars

Dr Macey said: “This discovery is exciting, because the environment is directly applicable to ancient martian environments. The team compared the water composition at Colour Peak to the water modelled for different martian environments. Using data from a wide array of models and data from rover missions the team could confirm that the aqueous environment at Axel Heiberg was indeed an excellent analogue for Mars.

“This is especially interesting in the light of the two upcoming missions to Mars, the NASA Perseverance Rover in 2020 and the ESA ExoMars rover in 2023. “

For more on the research findings, read the paper: The identification of sulfide oxidation as a potential metabolism driving primary production on late Noachian Mars published in Nature Scientific Reports.