A few specialist microbes survive conditions analogous to those of Mars'
early history, reports a new publication in Frontiers in Astronomy and Space
Science—and this may be thanks to a broad range of adaptations. The
hydrothermal crater lake of the Poás volcano in Costa Rica is one of the
most hostile habitats on the planet.
The water is ultra-acidic, full of toxic metals and the temperatures range
from comfortable to boiling. In addition, recurrent 'phreatic eruptions'
cause sudden explosions of steam, ash and rock. Despite such deadly
eruptions, hydrothermal environments may be where the earliest forms of life
began on Earth—and potentially also on Mars, if there ever was life.
Beyond discovering how life can survive these harsh conditions, studying
these microbes provides clues about if and how life might have existed on
Mars. "One of our key findings is that, within this extreme volcanic lake,
we detected only a few types of microorganisms, yet a potential multitude of
ways for them to survive," says first author Justin Wang, a graduate student
at the University of Colorado Boulder, in the United States. "We believe
they do this by surviving on the fringes of the lake when eruptions are
occurring. This is when having a relatively wide array of genes would be
useful."
This current interdisciplinary collaboration follows up on prior work from
2013. At that time, the researchers found that there was just one microbial
species coming from the Acidiphilium genus in the Poás volcanic lake.
Unsurprisingly, this type of bacteria is commonly found in acid mine
drainages and hydrothermal systems, and they are known to have multiple
genes adapted to diverse surroundings.
In the following years, there was a series of eruptions and the team
returned in 2017 to see whether there had been changes in the microbial
diversity, as well as to study the organisms' biochemical processes more
comprehensively. This latest work shows that there was a bit more
biodiversity, but still a dominance of the Acidiphilium bacteria.
Through DNA sequencing of the organisms in the lake samples, the team
confirmed that the bacteria had a wide variety of biochemical capabilities
to potentially help them tolerate extreme and dynamic conditions. These
included pathways to create energy using sulfur, iron, arsenic, carbon
fixation (like plants), both simple and complex sugars and bioplastic
granules (which microorganisms can create and use as energy and carbon
reserves during stress or starvation).
"We expected a lot of the genes that we found, but we didn't expect this
many given the lake's low biodiversity," says Wang. "This was quite a
surprise, but it is absolutely elegant. It makes sense that this is how life
would adapt to living in an active volcanic crater lake."
Despite the oftentimes lethal surroundings, hydrothermal systems provide
most of the key ingredients for the evolution of life, including heat, water
and energy. This is why leading theories for both Earth and Mars focus on
these locations. So far, previous efforts in search of life on Mars have
focused on streambeds or river deltas, but the authors suggest that more
attention should be given to the sites of past hot springs (which were
present on Mars for billions of years).
"Our research provides a framework for how 'Earth life' could have existed
in hydrothermal environments on Mars," explains Wang. "But whether life ever
existed on Mars and whether or not it resembles the microorganisms we have
here is still a big question. We hope that our research steers the
conversation to prioritize searching for signs of life in these
environments, for example there are some good targets on the crater rim of
Jezero Crater, which is where the Perseverance rover is right now."
Reference:
Microbial Survival in an Extreme Martian Analog Ecosystem: Poás Volcano, Costa
Rica, Frontiers in Astronomy and Space Science (2022). DOI: 10.3389/fspas.2022.817900
Tags:
Space & Astrophysics