Micro-organisms which live in extreme conditions could probably survive on Mars, and could be similar to forms of life that might exist on other planets, according to two recent studies.
In this week’s issue of Science, Lin et al report on a type of bacterium discovered in samples of groundwater obtained while drilling 2.8 km below the Earth’s surface in the Mponeng gold mine in South Africa. The bacteria are closely related to Desulfotomaculum kuznetsovii, a sulphate-reducing bacterium which lives near hydrothermal vents on the sea floor. They obtain their energy by combining the hydrogen produced by the actions of decaying uranium on water with the sulphate produced by geothermal activity, and do not appear to be dependent on the sun.
First author Li-Hung Lin, of National Taiwan University, says that the bacteria “probably represent relics of the surface community” which slipped deep underground many millions of years ago and have survived down there ever since. Lin’s team estimates that this microbial community could take anywhere between 45 and 300 years to double in size, and has sustained itself in this seemingly inhospitable environment for at least 20 million years. And, because of the slow but steady growth rate of the bacteria, and their resilience in the face of such harsh conditions, they could possibly sustain themselves beneath the surface of cold planets such as Mars.
The other study, published in the International Journal of Astrobiology, was carried out by astronomers from NASA’s Space Telescope Science Institute and microbiologists from the Center of Marine Biotechnology at the University of Maryland in Baltimore.
The astrobiology consortium investigated several types of archaea from Antarctica, where conditions have some similarities to those found on Mars. Two of these archaea, Methanococcoides burtonii, a methanogen which uses hydrogen and carbon dioxide for energy and produces methane as a waste product, and Halorubrum lacusprofundi, a halophilic bacterium adapted to living in extremely salty conditions, were able to survive and reproduce at temperatures as low as -2°C. This is about 5°C lower than what was thought to be the minimum limit for such microbial activity to take place. The study also showed that these microbes appear to have evolved a special mechanism to help them to survive at these very low temperatures. The mechanism involves the formation of cellular aggregates, and has never been observed in microbes before.
First author Neil Reid says “The low-temperature limits for both species fall within the temperature range experienced on present-day Mars and could permit survival and growth, particularly in sub-surface environments. This could expand the realm of the habitable zone, the area in which life could exist, to colder Mars-like planets.”
Archaea evolved around 3.5 billion years ago and are among the most ancient forms of life on Earth. Until recently, they were classified as bacteria but, in recent years, they have been shown to be genetically very different from bacteria, and have been reclassified into a kingdom of their own. Most extremophile microbes are archaea. For some, the existence of archaea is not just evidence that there may be life on other planets, it is also support for the theory that life on Earth was seeded from space.