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| The DNA sequence sheds new light on ecological
strategies that sustain microbial life in the world’s
oceans, according to Mary Ann Moran, professor of marine sciences.
(Photo by Peter Frey) |
Unexpected findings about the genetic makeup of a marine microbe
have given scientists a new perspective on how bacteria make a living
in the ocean—a view that may prove useful in wider studies
of marine ecology.
By deciphering and analyzing the DNA sequence of Silicibacter
pomeroyi, a member of an important group of marine bacteria,
scientists found that the metabolic strategies of marine bacterioplankton
are more diverse and less conventional than previously thought.
The study, which appeared in Nature in December, was led
by scientists in UGA’s department of marine sciences and at
the Institute for Genomic Research in Rockville, Md., along with
several collaborators. The project was sponsored by the National
Science Foundation.
Mary Ann Moran, professor of marine sciences at UGA and first author
of the Nature paper, says the DNA sequence sheds new light
on ecological strategies that sustain microbial life in the world’s
oceans.
“This genome is especially significant for the new theories
it will generate about the workings of the ocean,” she says.
“It provides new ideas and tools for investigating how microbes
control carbon, sulfur and nitrogen cycling on a global scale.”
In one surprise, the study found that S. pomeroyi has the
genetic tools to enable it to use inorganic compounds (such as inorganic
sulfur) for energy, which allows the microbes to use organic carbon
more efficiently in low-nutrient ocean environments.
Analysis of the genome sequence also showed that the microbe has
adapted in ways that allow it to take advantage of so-called “hot
spots” in the ocean—microscopic areas of the ocean that
are rich in organic matter, typically related to living and dead
microbial cells.
S. pomeroyi—named for Lawrence Pomeroy, a UGA biologist
who was a pioneer in the study of marine microbial ecology—is
a member of an important group of marine microbes, the Roseobacter
clade, found in both coastal and open oceans. Those bacteria account
for an estimated 15 percent of the production of new microbial
cells in the ocean.
The project was led by Moran and TIGR assistant investigator Naomi
Ward. Collaborators included Ron Kiene of the University of South
Alabama, Gary King of the University of Maine, Clay Fuqua of Indiana
University, Robert Belas of the University of Maryland’s Center
of Marine Biotechnology, and José González of the
University of La Laguna in Spain.
The S. pomeroyi genome offers the first real glimpse of
the genetic material harbored by the Roseobacter group of bacteria,
which have evolved metabolic strategies that allow them to flourish
in marine environments. While scientists knew from laboratory studies
that the microbe would metabolize sulfur, the genome sequence offered
several surprises about how bacteria make a living in the ocean.
One unexpected finding from the genomic analysis was evidence of
“lithoheterotrophy,” the ability of marine bacteria
that typically rely on organic carbon fixed by primary producers
as their source of cell material to also use inorganic compounds
(in this case, carbon monoxide and sulfur) for energy. In that way,
the microbes can save more of the organic compounds for biosynthetic
processes—allowing more efficient use of organic carbon in
an environment that has little to go around.
“The microbe’s predicted ability to use such inorganic
compounds was surprising,” says Ward. “This study demonstrates
how genome analysis allows us to propose new hypotheses of biological
activity for a well-studied organism. We were able to test and confirm
some of those hypotheses in the lab, providing more evidence for
this lithoheterotropic strategy.”
Another significant finding was that S. pomeroyi has numerous
adaptations to living in association with ocean particles, which
allows it to take advantage of marine “hot spots”—rich
areas of organic matter floating in an otherwise nutrient-poor ocean
environment. The “hot spots” concept was first proposed
more than a decade ago.
Moran says the S. pomeroyi sequence “demonstrates
that genomes of ecologically relevant cultured microbes have enormous
potential to move marine biogeochemical research forward at a rapid
pace, both by generating hypotheses about how the ocean works and
by providing tools to investigate these hypotheses in the ocean.”
Moran and colleagues at UGA and Ward and associates at TIGR headed
up the project, including genome sequencing and annotation and experimental
demonstration of properties suggested by the genome sequence. Three
other groups joined the project after annotation began because of
their expertise in specific genes. |
