A CU-Boulder-led team has discovered some rare, primitive microorganisms on high volcanoes in South America that may be fueled by drifting gases in the region rather than photosynthesis. Image courtesy University of Colorado |
A
team led by the University of Colorado Boulder looking for organisms
that eke out a living in some of the most inhospitable soils on Earth
has found a hardy few.
A
new DNA analysis of rocky soils in the Martian-like landscape on some
volcanoes in South America has revealed a handful of bacteria, fungi and
other rudimentary organisms called archaea, which seem to have a
different way of converting energy than their cousins elsewhere in the
world.
“We
haven’t formally identified or characterized the species,” said Ryan
Lynch, a CU-Boulder doctoral student involved in the study. “But these
are very different than anything else that has been cultured.
Genetically, they’re at least 5% different than anything else in the DNA
database of 2.5 million sequences.”
Life
gets little encouragement on the incredibly dry slopes of the tallest
volcanoes in the Atacama region, where CU-Boulder Professor Steve
Schmidt and his team collected soil samples. Much of the sparse snow
that falls on the terrain sublimates back to the atmosphere soon after
it hits the ground, and the soil is so depleted of nutrients that
nitrogen levels in the scientists’ samples were below detection limits.
Ultraviolet
radiation in the high-altitude environment can be twice as intense as
in a low-elevation desert, said Schmidt of CU-Boulder’s ecology and
evolutionary biology department. While the researchers were on site,
temperatures dropped to 14 F one night and spiked to 133 F the next day.
How
the newfound organisms survive under such circumstances remains a
mystery. Although Ryan, Schmidt and their colleagues looked for genes
known to be involved in photosynthesis and peered into the cells using
fluorescent techniques to look for chlorophyll, they couldn’t find
evidence that the microbes were photosynthetic.
Instead,
they think the microbes might slowly generate energy by means of
chemical reactions that extract energy and carbon from wisps of gases
such as carbon monoxide and dimethylsulfide that blow into the desolate
mountain area. The process wouldn’t give the bugs a high-energy yield,
Lynch said, but it could be enough as it adds up over time. A paper on
the findings has been accepted by the Journal of Geophysical
Research-Biogeosciences, published by the American Geophysical Union.
While
normal soil has thousands of microbial species in just a gram of soil,
and garden soils even more, remarkably few species have made their home
in the barren Atacama mountain soil, the new research suggests. “To find
a community dominated by less than 20 species is pretty amazing for a
soil microbiologist,” Schmidt said.
He
has studied sites in the Peruvian Andes where, four years after a
glacier retreats, there are thriving, diverse microbe communities. But
on these volcanoes on the Chile-Argentina border, which rise to
altitudes of more than 19,685 feet and which have been ice-free for
48,000 years, the bacterial and fungal ecosystems have not undergone
succession to more diverse communities. “It’s mostly due to the lack of
water, we think,” he said. “Without water, you’re not going to develop a
complex community.”
“Overall,
there was a good bit lower diversity in the Atacama samples than you
would find in most soils, including other mountainous mineral soils,”
Lynch said. That makes the Atacama microbes very unusual, he added.
They probably had to adapt to the extremely harsh environment, or may
have evolved in different directions than similar organisms elsewhere
due to long-term geographic isolation.
Growth
on the mountain might be intermittent, Schmidt suggested, especially if
soils only have water for a short time after snowfall. In those
situations, there could be microbes that grow when it snows, then fall
dormant, perhaps for years, before they grow again. High-elevation sites
are great places to study simple microbial communities, ecosystems that
haven’t evolved past the very basics of a few bacteria and fungi,
Schmidt said.
“There
are a lot of areas in the world that haven’t been studied from a
microbial perspective, and this is one of the main ones,” he said.
“We’re interested in discovering new forms of life, and describing what
those organisms are doing, how they make a living.”
Schmidt’s
lab, along with others, is studying how microorganisms travel from one
site to another. One common method of microbe transport is through the
air—they’re caught up in winds, sucked up into clouds, form rain
droplets and then fall back to the ground somewhere else as
precipitation.
But
on mountains like Volcán Llullaillaco and Volcán Socompa, the high UV
radiation and extreme temperatures make the landscape inhospitable to
outside microbes. “This environment is so restrictive, most of those
things that are raining down are killed immediately,” Schmidt said.
“There’s a huge environmental filter here that’s keeping most of these
things from growing.”
The
next steps for the researchers are laboratory experiments using an
incubator that can mimic the extreme temperature fluctuations to better
understand how any organism can live in such an unfriendly environment.
Studying the microbes and finding out how they can live at such an
extreme can help set boundaries for life on Earth, Schmidt said, and
tells scientists what life can stand. There’s a possibility that some of
the extremophiles might utilize completely new forms of metabolism,
converting energy in a novel way.
Schmidt
also is working with astrobiologists to model what past conditions were
like on Mars. With their rocky terrain, thin atmosphere and high
radiation, the Atacama volcanoes are some of the most similar places on
Earth to the Red Planet.
“If
we know, on Earth, what the outer limits for life were, and they know
what the paleoclimates on Mars were like, we may have a better idea of
what could have lived there,” he said.
Other
paper authors included Andrew King of Ecosystem Sciences, CSIRO Black
Mountain in Acton, Australia; Mariá Farías of Laboratorio de
Investigaciones Microbiologicas de Lagunas Andinas, Planto Piloto de
Procesos Industriales Microbiologicas, CCT, CONICET in Tucuman,
Argentina; Preston Sowell of Geomega, an environmental consulting firm
in Boulder; and Christian Vitry of Museo de Arqueologia de Alta Montana
in Salta, Argentina.
Source: University of Colorado Boulder
