Microorganisms have adapted to one of the harshest environments on Earth, a sulphurous and acidic lake that is considered an analogue to ancient lakes on Mars
Bacteria have adapted to survive the extreme conditions of a crater lake in the active Poás volcano in Costa Rica, known as Laguna Caliente. These microorganisms provide clues to how potential life may have existed under similar circumstances on Mars.
Situated at 2300 metres above sea level, Laguna Caliente is one of the harshest environments on Earth. It is extremely sulphurous and highly acidic, with pH values ranging between -0.87 and 1.5. The lake is also subject to widely fluctuating temperatures, ranging from 38°C to 90°C.
Laguna Caliente has similar mineral compositions to Gusev crater on Mars, which was explored by NASA’s Spirit rover when it landed there in 2004. This suggests that lakes that may have existed on Mars in the past would also have been acidic and hot, says Justin Wang at the University of Colorado Boulder.
To characterise Laguna Caliente’s microbiology, Wang and his team analysed the DNA of microorganisms found in samples of lake fluid, clumps of sulphur and sediment in 2013 and 2017.
The researchers found that the samples had a remarkably low biodiversity compared with most ecosystems on Earth. The microorganisms were mostly bacteria from the genus Acidiphilium.
“We either expected to find nothing at all because this [environment] was so extreme or to find multiple organisms because that’s how most microorganisms live with each other,” says Wang. “They rely on each other in very symbiotic interactions.”
They found that the bacteria had developed specialised adaptations to withstand the lake’s hostile conditions, such as their ability to metabolise energy from sulphur. But one of the most surprising findings was that the bacteria create bioplastics that act as energy stores, says Wang. “We believe that they use these bioplastics to survive on the fringe of the lake when eruptions are occurring,” he says.
The findings suggest that life is possible in the extreme environments that may have existed in ancient crater lakes on Mars.
“The results hint that the minerals formed under these conditions on Mars might perhaps be associated with some remains or traces of life.” says Sean McMahon at the University of Edinburgh in the UK. “Even if these environments were habitable, we may never know whether they were actually inhabited unless they produced fossils of some kind.”
Journal reference: Frontiers in Astronomy and Space Sciences, DOI: 10.3389/fspas.2022.817900
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