on Microbes and its Significance
|Key player in
global warming: Methanosarcina acetivorans is
Heroes of the global
carbon cycle are methanogens microbes at the bottom
of the food chain who break down the waste products
of other organisms and release methane gas into the
atmosphere. Scientists have now sequenced one of the
most versatile methanogens, an organism called Methanosarcina
species live in oil wells, sewage lagoons, trash dumps,
decaying leaves, stream sediments, and the stomach of
cows, among other places. They subsist on a diverse
menu of energy sources, including acetate. With the
genome sequenced, researchers have begun to search for
genes responsible for the organism's capacity to adapt
and break down a variety of waste products
"This is an
incredibly versatile organism," says James Galagan,
who led the annotation and analysis effort at the Whitehead
Institute Center for Genome Research in Cambridge, Massachusetts.
"It is a sink for lots of diverse waste products;
the microbe processes these products and then releases
methane back into the global carbon cycle."
acetivorans belongs to the family of archaea, an
ancient branch of life that is distinct from plants,
animals, and bacteria. The archaea are the least understood
domain of life, and researchers will use the sequence
to investigate the biology of these organisms, including
are critical players in the global carbon cycle and
have potential uses for addressing human problems,"
says William W. Metcalf, a microbiologist at the University
of Illinois at Urbana-Champaign, and a member of the
both a potential alternative energy source and a potent
greenhouse gas. There is an enormous amount of methane
at the bottom of the oceans; and methane reflects heat
far better than carbon dioxide does. Metcalf says that
methane is both "a staggering untapped source of
natural energy" and "a fairly frightening
contributor" to global warming.
The biggest surprise
of the sequencing project was the size of the genome.
Early estimates were either wrong or the researchers
did not believe it could be as large as it turned out
to be. The genome of M. acetivorans C2A is
by far the largest of all sequenced archaeal genomes.
With 5.7 million base pairs, it is more than three times
as large as two previously sequenced methanogens, Methanobacterium
thermoautotrophicum and Methanococcus jannaschii.
genomes of closely related species vary so much in size
raises a lot of biological questions," says Galagan.
"We are now in a position to answer those questions
with the genome sequence." The researchers identified
about 4,500 genes of which nearly 200 genes are related
to methanogenesis. The findings are published in Genome
the genome to a rain forest with biodiversity waiting
to be explored. Already, the researchers have made some
interesting discoveries. For instance, M. acetivorans
appears to have the capacity to propel itself, although
no one has ever seen it do so. The researchers identified
genes for flagella and for chemotaxis, the process of
moving purposefully toward a chemical. "These genes
are pretty strong evidence that the organism is able
to move under the right circumstances," says Galagan.
acetivorans was sequenced in part because genetic
tools are available to modify the organism in the laboratory,
making it a model species for methanogens. Metcalf's
laboratory, among others, created some genetic mutants,
and in recent months they have shipped these to researchers
interested in testing findings from the sequence.
Despite the genome's
size, the sequencing was done relatively quickly. Then
the researchers began the process of correcting and
annotating the sequence. For two months, the Whitehead
team corresponded with experts around the world about
the sequence. This culminated in a two-day genome analysis
meeting at the Whitehead Institute.
believe the best way to understand a genome is to bring
together as many experts as possible to analyze the
sequence," says Galagan. One participant in the
two-day meeting told him, "This was the most fun
I've had in science in the last decade."
Genome News Network 2002
a Key Component of Global Environmental Change:
to a new report from the American Society for Microbiology
(ASM), microbial activity can play a significant role
in slowing adverse effects of greenhouse gases and other
global environmental changes.
report, "Global Environmental Change: Microbial
Contributions, Microbial Solutions," points out
that the basic chemistry of Earth's surface is determined
by biological activity, especially that of the many
trillions of microbes in soil and water. Microbes make
up the majority of the living biomass on Earth and,
as such, have major roles in the recycling of elements
vital to life.
the microbial world can contribute to as well as mitigate
global change, its activities are important to understand
as a sound basis for policy decisions and regulations.
to Dr. James M. Tiedje, Michigan State University, an
author of the report who chairs ASM's Committee on Environmental
Microbiology, stated that "we must better understand
the human-microbe partnership so that environmental
decisions that impact microbial processes will achieve
appropriate balances in the atmosphere and biosphere.
Otherwise, we will be increasingly challenged by unprecedented
roles in global change include producing and consuming
atmospheric gases that affect climate; mobilizing toxic
elements such as mercury, arsenic and selenium; and
producing toxic algal blooms and creating oxygen depletion
zones in lakes, rivers and coastal environments (eutrophication).
Furthermore, the incidence of microbial diseases such
as plague, cholera, Lyme disease, and West Nile Virus
are linked to global change.
|The report makes four
recommendations to enhance microbiological solutions to
of microbiological processes from organism to ecosystem
level. This will lead, in part, to an improved understanding
of the global carbon budget, eutrophication and the
changes in greenhouse gases that affect climate.
and harness the abilities of microbes that transform
the active greenhouse trace gases and toxic elements.
multi-year research programs that draw on microbiology
and partner disciplines such as earth and atmospheric
sciences to gain an integrated understanding of complex
global change problems.
training scientists and policy makers for the future's
complex environmental problems.
working in broad, multidisciplinary research programs
can help provide answers for a question of fundamental
importance: How can microbial populations and activities
be managed to sustain the biosphere and its diverse
life forms while promoting human welfare?
Reported by ASM's Public and Scientific Affairs Board.
Authors of the report include Dr. Gary M. King, University
of Maine; Dr. David Kirchman, University of Delaware;
Dr. Abigail Salyers, University of Illinois; Dr. William
Schlesinger, Duke University, and Dr. James Tiedje,
Michigan State University).