Now, a team of
researchers, led
by marine microbial ecologist Mary Ann Moran at the "This new gene
offers a
powerful tool to study the question of how bacterioplankton are
involved with
ocean-atmosphere sulfur exchange," said Moran. The study was
published today in
the journal Science. Other authors of the paper include: William B.
Whitman, of
the UGA department of microbiology; Erinn Howard, James Henriksen,
Alison
Buchan and Chris Reich, present or former doctoral students at UGA;
current UGA
postdoctoral associate Helmut Bürgmann and former postdocs
Kimberly Mace and
Jose González; former UGA undergraduate Rory Welsh; UGA lab
coordinator Wenying
Ye; Samantha Joye, biogeochemist in the department of marine sciences
at UGA;
and Ronald Kiene of the department of marine sciences at the University
of
South Alabama. Much of the sulfur
in the
atmosphere comes from the surface of oceans and a compound called
dimethlysulfide or DMS. Marine bacterioplankton control how much sulfur
rises
into the atmosphere by converting a compound called DMSP either to DMS
or to
sulfur compounds that are not climatically active. Moran and her team
discovered, in
two groups of bacterioplankton, the gene that controls whether or not
these sea
drifters create DMS that rises into the air or another compound that
doesn't.
The implications are considerable, since atmospheric sulfur is involved
with
everything from acid rain to global warming. "This breakthrough
in the
microbial physiology of DMSP metabolism opens the door to finally
understanding
the biology and ecology of this globally important process," said
Whitman.
"These are necessary steps in learning how our planet works. They have
very practical implications as well and could help ameliorate the
climate
change caused by emissions of greenhouse gases." Moran agreed. "We knew bacteria
played a
key role in the cycling of marine sulfur, but the discovery of this
gene allows
us to pinpoint how and when bacteria control this process," she said.
This
flow provides a key feedback loop in theories of global climate
regulation for
which biotic processes are central elements. The researchers
discovered that
the bacterioplankton in the Roseobacter and SAR11 groups are the
primary
plankton involved with directing DMSP away from DMS and thus making
sulfur
unavailable to atmospheric processes. (Roseobacter largely grow in
coastal
waters, while SAR11 are more prevalent in open seas.) Plankton can be
divided into
broad functional groups. Phytoplankton live near the water's surface
and
flourish through photosynthesis. Zooplankton are small protozoans that
feed on
other plankton, and bacterioplankton include bacteria and Archaea (a
relatively
newly discovered category of sea life) that re-mineralize organic
material down
the water column. While researchers
had known for
some time that phytoplankton can degrade DMSP to DMS, efforts to
predict global
patterns of ocean-atmosphere DMS flux based solely on the abundance of
phytoplankton
had been unsuccessful. Moran and her team thus became interested in the
other
plankton that were involved. "We had an
advantage,
because we are able to grow Roseobacter in the lab," said Moran. "But
much less was known about how SAR11 'make a living.'" Dramatic advances in
understanding how bacterioplankton work have occurred in the past few
years
with the availability of new genomic data. The scientists searched
genome
fragments of bacterioplankton that grow in the Sargasso Sea, looking
for
specific gene sequences that would show how these sea creatures use
sulfur
compounds. (The Sargasso Sea is an elongated region in the middle of
the "This project has
brilliantly come full circle," said Matthew Kane, program director with
the National Science Foundation, which supported the research.
"Isolation
and discovery of a novel, keystone bacterium from the ocean, and
sequencing of
its genome enabled the team to work out the genes involved in the DMSP
cycle.
They now have been able to show the distribution and abundance of one
of these
genes back in environmental populations, thus revealing the previously
hidden
role that marine microbes play in the global sulfur cycle." The discovery of the
bacterial
gene switch in these two groups of bacterioplankton will open new areas
of
research, since DMSP synthesis may account for almost all of the
marine-created
atmospheric sulfur. The findings also expand our knowledge of how these
marine
taxa are involved in the routing of carbon and sulfur into the
microbial food
web.
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