Embargoed until 2:00 p.m., EDT
NSF PR 01-63 - August 8, 2001
Media contact:
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Cheryl Dybas
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(703) 292-8070
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cdybas@nsf.gov
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Program contact:
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Phil Taylor
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(703) 292-8582
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prtaylor@nsf.gov
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New Source of Natural Fertilizer Discovered in
Oceans
New findings suggest that the deep ocean is teeming
with organisms that produce essential natural fertilizers.
A National Science Foundation (NSF)-funded research
team led by Jonathan Zehr, a marine scientist at the
University of California, Santa Cruz, has discovered
a previously unknown type of photosynthetic bacteria
that fixes nitrogen, converting nitrogen from the
atmosphere into a form other organisms can use. The
researchers reported their findings in the August
9 issue of the journal Nature. Zehr has also
found evidence that many additional kinds of nitrogen-fixing
bacteria live in the open ocean.
"This discovery points to how little we know about
the organisms that drive ocean biogeochemical processes,"
says Phil Taylor, director of NSF's biological oceanography
program. "It may have profound influences on our thinking
about and modeling of the global ocean nitrogen and
carbon cycles."
Although nitrogen accounts for nearly 80 percent of
the Earth's atmosphere, most organisms can use it
only when it is "fixed" to other elements, to make
compounds such as ammonia or nitrate. As a component
of proteins, nitrogen is essential to all known forms
of life.
Zehr and his coworkers found the nitrogen-fixing bacteria,
which they have grown in the laboratory, in water
samples collected from the Pacific Ocean near Hawaii.
The organisms appear to belong to the genus Synechocystis,
a group of cyanobacteria (photosynthetic bacteria
formerly known as blue-green algae) that includes
both marine and freshwater species. The newly discovered
nitrogen-fixers appear to be active at greater depths
and over longer time periods than other marine cyanobacteria
known to fix nitrogen in the open ocean.
On land, nitrogen-fixing bacteria are a known quantity,
residing in the roots of legumes like peas and beans.
While many nitrogen-fixing cyanobacteria have been
found in coastal waters, very few are known to occur
in the open ocean.
"It appears that there is much more nitrogen fixation
than we know about," Zehr said. "In the open ocean,
there are only one or two organisms known to fix nitrogen.
They probably can't account for all the nitrogen getting
fixed." The amount of nitrogen fixation in the open
ocean has implications for global warming because
nitrogen stimulates the growth of marine algae, which
absorb carbon dioxide from the atmosphere.
Over the past 12 years, Zehr has uncovered evidence
of dozens of nitrogen-fixing bacteria by looking not
for the organisms themselves but for their DNA fingerprints
-- specifically, for a gene encoding the protein responsible
for nitrogen fixation.
The nitrogen-fixing marine Synechocystis is
the first of these organisms Zehr's team has succeeded
in cultivating in the laboratory. What emerged was
a strain of nitrogen-fixing bacteria that are about
100 times as large as typical photosynthetic ocean
bacteria. "They're like basketballs, compared to the
pins of light we're used to looking at," Zehr said.
The relatively large size of these cyanobacteria and
their abundance suggest that they make a significant
contribution to nitrogen fixation in the ocean. "There's
potentially as much biomass of these bacteria as of
the other two known nitrogen-fixers in the open ocean
combined," Zehr said.
The new bacteria are abundant as deep as 100 to 200
meters below the surface, compared to 50 meters for
the most productive known nitrogen-fixer. And unlike
the previously known nitrogen-fixers, which are only
active in warm seasons, the new bacteria have shown
activity in February.
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