They are sustained primarily by chemicals created by the natural irradiation of water molecules. Results of this research may have implications for life on Mars.
From:
University of Rhode Island
February 26, 2021 -- A team of
researchers from the University of Rhode Island's Graduate School of
Oceanography and their collaborators have revealed that the abundant microbes
living in ancient sediment below the seafloor are sustained primarily by
chemicals created by the natural irradiation of water molecules.
The team discovered that the creation of
these chemicals is amplified significantly by minerals in marine sediment. In
contrast to the conventional view that life in sediment is fueled by products
of photosynthesis, an ecosystem fueled by irradiation of water begins just
meters below the seafloor in much of the open ocean. This radiation-fueled
world is one of Earth's volumetrically largest ecosystems.
The research was published today in the
journal Nature Communications.
"This work provides an important
new perspective on the availability of resources that subsurface microbial
communities can use to sustain themselves. This is fundamental to understand
life on Earth and to constrain the habitability of other planetary bodies, such
as Mars," said Justine Sauvage, the study's lead author and a postdoctoral
fellow at the University of Gothenburg who conducted the research as a doctoral
student at URI.
The process driving the research team's
findings is radiolysis of water -- the splitting of water molecules into
hydrogen and oxidants as a result of being exposed to naturally occurring
radiation. Steven D'Hondt, URI professor of oceanography and a co-author of the
study, said the resulting molecules become the primary source of food and
energy for the microbes living in the sediment.
"The marine sediment actually
amplifies the production of these usable chemicals," he said. "If you
have the same amount of irradiation in pure water and in wet sediment, you get
a lot more hydrogen from wet sediment. The sediment makes the production of
hydrogen much more effective."
Why the process is amplified in wet
sediment is unclear, but D'Hondt speculates that minerals in the sediment may
"behave like a semiconductor, making the process more efficient."
The discoveries resulted from a series
of laboratory experiments conducted in the Rhode Island Nuclear Science Center.
Sauvage irradiated vials of wet sediment from various locations in the Pacific
and Atlantic Oceans, collected by the Integrated Ocean Drilling Program and by
U.S. research vessels. She compared the production of hydrogen to similarly
irradiated vials of seawater and distilled water. The sediment amplified the
results by as much as a factor of 30.
"This study is a unique combination
of sophisticated laboratory experiments integrated into a global biological
context," said co-author Arthur Spivack, URI professor of oceanography.
The implications of the findings are
significant.
"If you can support life in
subsurface marine sediment and other subsurface environments from natural
radioactive splitting of water, then maybe you can support life the same way in
other worlds," said D'Hondt. "Some of the same minerals are present
on Mars, and as long as you have those wet catalytic minerals, you're going to
have this process. If you can catalyze production of radiolytic chemicals at
high rates in the wet Martian subsurface, you could potentially sustain life at
the same levels that it's sustained in marine sediment."
Sauvage added, "This is especially
relevant given that the Perseverance Rover has just landed on Mars, with its
mission to collect Martian rocks and to characterize its habitable
environments."
D'Hondt said the research team's
findings also have implications for the nuclear industry, including for how
nuclear waste is stored and how nuclear accidents are managed. "If you
store nuclear waste in sediment or rock, it may generate hydrogen and oxidants
faster than in pure water. That natural catalysis may make those storage
systems more corrosive than is generally realized," he said.
The next steps for the research team
will be to explore the effect of hydrogen production through radiolysis in
other environments on Earth and beyond, including oceanic crust, continental
crust and subsurface Mars. They also will seek to advance the understanding of
how subsurface microbial communities live, interact and evolve when their
primary energy source is derived from the natural radiolytic splitting of
water.
https://www.sciencedaily.com/releases/2021/02/210226103802.htm
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