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"Feed" on Earth's Ocean-Bottom Crust
Bacteria "Feed" on Earth's Ocean-Bottom
Crust
Rocks on and under seafloor
offer feast for microbes
Rocks made of basalt on and under
the ocean bottom harbor surprising numbers of deep-sea bacteria.
Seafloor bacteria on ocean-bottom
rocks are more abundant and diverse than previously thought,
appearing to "feed" on the planet's oceanic
crust, according to results of a study reported in
this week's issue of the journal Nature.
The findings pose intriguing questions about ocean chemistry
and the co-evolution of Earth and life.
Once considered a barren plain dotted with
hydrothermal vents, the seafloor's rocky
regions appear to be teeming with microbial life, say scientists
from the Woods Hole Oceanographic Institution (WHOI) in Woods
Hole, Mass., University of Southern California (USC) in Los
Angeles, and other institutions.
While seafloor microbes have been detected
before, this is the first time they have been quantified.
Using genetic analyses, Cara Santelli of WHOI, Katrina Edwards
of USC, and colleagues found three to four times more bacteria
living on exposed rock than in the waters above.
"Initial research predicted that life could in fact
exist in such a cold, dark, rocky environment," said
Santelli. "But we really didn't expect to find it thriving
at the levels we observed."
Surprised by this diversity, the scientists tested more than
one site and arrived at consistent results, making it likely,
according to Santelli and Edwards, that rich microbial life
extends across the ocean floor.
"This may represent the largest surface area on Earth
for microbes to colonize," said Edwards.
"These scientists used modern molecular
methods to quantify the microbial biomass and estimate the
diversity of microbes in deep-sea environments," said
David Garrison, director of the National Science Foundation
(NSF)'s Biological Oceanography Program. NSF's Ridge
2000 program funded the research. "We now know that this
remote region is teeming with microbes, more so than anyone
had guessed."
Biologist Katrina Edwards of the University of Southern California discusses her research on seafloor bacteria on ocean-bottom rocks.
Santelli and Edwards also found that the
higher microbial diversity on ocean-bottom rocks
compared favorably with other life-rich places in the oceans,
such as hydrothermal vents.
These findings raise the question of where these bacteria
find their energy, Santelli said.
"We scratched our heads about what was supporting this
high level of growth," Edwards said.
With evidence that the oceanic crust supports more bacteria
than overlying water, the scientists hypothesized that reactions
with the rocks themselves might offer fuel for life.
In the lab, they calculated how much biomass could be supported
by chemical reactions with the rocky basalt. They then compared
this figure to the actual biomass measured. "It was completely
consistent," Edwards said.
Bacteria form large undersea mats in some areas of the ocean's deepest realms.
This discovery lends support to the idea
that bacteria survive on energy from Earth's crust, a process
that could add to our knowledge about the deep-sea
carbon cycle and the evolution of life.
Many scientists believe that shallow water,
not deep water, is better suited for cradling
the planet's first life forms. Up until now, dark, carbon-poor
ocean depths appeared to offer little energy, and rich environments
like hydrothermal vents were thought to be relatively sparse.
But the newfound abundance of seafloor microbes
makes it possible that early life thrived--and perhaps began--on
the seafloor.
"If we can really nail down what's going on, there are
significant implications," Edwards said. "I hope
that people turn their heads and notice: there's life down
there."
In addition to Santelli and Edwards, the paper's co-authors
are: Beth Orcutt of USC; Erin Banning of WHOI; Wolfgang Bach
of WHOI and Universität Bremen; Craig Moyer of Western
Washington University; Mitchell Sogin of the Marine Biological
Laboratory; and Hubert Staudigel of the Scripps Institution
of Oceanography.
The research was also funded by the NASA Astrobiology Institute
and Western Washington University.
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