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"This new gene offers a powerful tool to study the question of how
these plankton are involved with sulfur exchange between the ocean and
atmosphere," said Mary Ann Moran, marine microbial ecologist at the
University of Georgia. Moran and her colleagues published their
findings in the Oct. 26, 2006, issue of the journal Science.
Much of the sulfur in the atmosphere comes from the surface of oceans,
from a compound called dimethlysulfide, or DMS. Marine plankton
control how much sulfur rises into the atmosphere by converting a
compound called DMSP, or dimethylsulfoniopropionate, to DMS or to
sulfur compounds that are not climatically active. Moran and her team
discovered a gene that controls whether or not these sea drifters
create DMS that rises into the air.
"Isolating and discovering a novel, keystone bacterium from the ocean
first, and then sequencing its genome enabled this team to find the
genes involved in the DMSP cycle," said Matthew Kane, program director
in the National Science Foundation (NSF) Division of Molecular and
Cellular Biosciences, which supported the research. "The research has
revealed the previously hidden role that marine microbes play in the
global sulfur cycle."
The researchers discovered that microscopic plankton that fall under
the Roseobacter and SAR11 organism groups are the primary plankton
involved in directing DMSP away from forming DMS, and thus making
sulfur unavailable to atmospheric processes.
Dramatic advances in understanding how these plankton work have
developed in the past few years with the availability of new genomic
data. The scientists searched genome fragments of these plankton,
looking for specific gene sequences that would show how the plankton
use sulfur compounds.
"This breakthrough in the microbial physiology of DMSP metabolism
opens the door to understanding the biology and ecology of this
globally important process," said William Whitman, a microbiologist at
the University of Georgia and co-author of the Science paper. The
discovery of a bacterial gene switch in these two groups of plankton
will open new areas of research, since DMSP synthesis may account for
almost all marine-created atmospheric sulfur. The findings also expand
knowledge of how these marine organisms are involved in the routing of
carbon and sulfur into the microbial food web.
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