NatioNal academy of ScieNceS NatioNal academy of eNgiNeeriNg iNStitute of mediciNe NatioNal reSearch couNcil
H
umankind has benefited enormously from the study of microbes since their
discovery in the 17th century. However, such benefits have come from
the study of just a miniscule fraction of the millions of species of microbes
in the environment. In addition, scientists are realizing the importance
of studying the collective properties of communities of microbes, which perform com-
plex tasks essential to the health of human beings and our planet. The emerging field of
metagenomics opens the door to exploring the vast array of microbes unstudied to date
and to investigating entire microbial communities. Through a deeper understanding of the
microbes that sustain life on Earth, the metagenomics approach offers the promise of an
incredible array of new benefits.
U n d E r s T a n d I n g O U r
MIcrObIal PlanET
T h e N e w S c i e N c e o f M e T a g e N o M i c S
MICROBIAL COMMUNITIES
support all
life on Earth;
metagenomics
is a revolutionary
new approach to understanding the charac-
teristics of our microbial world. This new
science opens doors to a tremendous amount
of scientific exploration and can help address
some of the most complex medical, environ-
mental, agricultural, and economic challenges
of todayâs world.
a New TooL foR ScieNTific
eXPLoRaTioNâŚ
MeDiciNe:
Examining how the microbial communities
that normally inhabit our bodies affect human health can
lead to new strategies for diagnosing, treating, and pos-
sibly preventing diseases.
Life ScieNceS:
deciphering how microbial communi-
ties function can partially answer fundamental questions
about microbial, plant, and animal biology and greatly
enhance our understanding of ecology and evolution.
eaRTh ScieNceS:
Exploring how microbial communi-
ties in the soil and in the ocean affect atmospheric
balances and environmental conditions can help us under-
stand, predict, and potentially address global changes.
aBoUT The NaTioNaL acaDeMieS
The national academiesâthe national academy of sciences, national academy of
Engineering, Institute of Medicine, and the national research councilâprovide a
public service by working outside the framework of government to ensure independent
advice on matters of science, technology, and medicine. They enlist committees of
the nation's top scientists, engineers, and other expertsâall of whom volunteer their
time to study specific concerns. The results of these deliberations are authoritative,
peer-reviewed reports that have inspired some of the nationâs most significant efforts to
improve the health, education, and welfare of the population.
This booklet was derived from the national research council report
The New Science of
Metagenomics: Revealing the Secrets of Our Microbial Planet
(2007) by the committee on
Metagenomics: challenges and Funcitonal applications.
http://books.nap.edu/catalog.
php?record_id=11902
coMMiTTee oN MeTageNoMicS: chaLLeNgeS aND fUNcTioNaL aPPLicaTioNS
Jo handelsman (co-chair), University of Wisconsin-Madison; James M. Tiedje (co-
chair), Michigan state University;
Lisa alvarez-cohen, University of california,
berkeley;
Michael ashburner, University of cambridge; isaac K. o. cann, University
of Illinois, Urbana-champaign;
edward f. DeLong, Massachusetts Institute of
Technology;
w. ford Doolittle, dalhousie University; claire M. fraser-Liggett,
The Institute for genomic research;
adam godzik, The burnham Institute; Jeffrey i.
gordon, Washington University school of Medicine; Margaret Riley, University of
Massachusetts, amherst;
Molly B. Schmid, Keck graduate Institute; ann h. Reid (study
director), national research council.
reports from the national academies are available from the national academies Press,
500 Fifth street, nW, Washington, dc 20001; 800-624-6242;
http://www.nap.edu.
reports are available online in a fully searchable format.
This booklet and related materials are available at
http://dels.nas.edu/metagenomics.
This publication was written by anne Jurkowski and ann reid and was designed by
Van nguyen. cover art by nicolle rager Fuller (
www.sayo-art.com); page 3 watermark
image from U.s. department of Energy; page 17 photo by Jeff Miller, University of
Wisconsin-Madison.
copyright 2007 by the national academy of sciences. all rights reserved.
heLPiNg aDDReSS The chaLLeNgeS
of ToDaYâS woRLDâŚ
aLTeRNaTiVe eNeRgY:
Harnessing the power of
microbial communities may lead to more sustainable
and environmentally friendly biologically-based ener-
gy sources.
eNViRoNMeNTaL ReMeDiaTioN:
developing
microbe-based tools for monitoring environmental
damage and cleaning up oil spills, groundwater, sew-
age, nuclear waste, and other hazards may help restore
healthy ecosystems.
BioTechNoLogY:
Taking advantage of the
diverse abilities of microbial communities may lead
to the development of beneficial industrial, food, and
health products.
agRicULTURe:
gaining a better understanding of
the beneficial microbes living in, on, and around do-
mestic plants and animals can contribute to improved
methods for detecting diseases in crops, livestock, and
food products and can facilitate the development of
farming practices that take advantage of the natural
alliances among microbes and plants and animals.
BioDefeNSe aND MicRoBiaL foReNSicS:
studying the dna and biochemical fingerprints of
microbial communities helps specialists monitor known
and potential pathogens, create more effective vaccines
and treatments against potential bioterror agents, and
reconstruct events in which microbes have played a role.
T
rillions
of
f
riends
âŚM
icrobes
M
ake
H
uMan
l
ife
P
ossible
3
W
indoW
To
THe
M
icrobial
u
niverse
: T
He
n
eW
s
cience
of
M
eTagenoMics
5
What Is Metagenomics?
How Does Metagenomics Work?
a
PPlicaTions
: W
HaT
M
eTagenoMics
c
an
d
o
9
The World Within: Learning from the Microbial Inhabitants of the Human Body
Global Impacts: The Role of Microbes in Maintaining Atmospheric Balances
Bioenergy: Harnessing Microbial Power
Smart Farming: How Microbes Help Our Crops
Cleaning Up: Remediation of Environmental Contamination
g
eTTing
THe
M
osT
o
uT
of
n
eW
s
cienTific
a
dvances
16
s
uMMary
19
CONTENTS
UNDERSTANDING OUR MICROBIAL PLANET
UNDERSTANDING OUR MICROBIAL PLANET
TRILLIONS OF FRIENDS âŚ
MICROBES MAkE HUMAN
LIFE POSSIBLE
M
ore than three billion years ago, organisms too small to be seen
began a process that ultimately would enable the evolution of all
complex life on Earth. At that time, Earth was very different from
what it is today. All life was confined to single-celled microscopic
organisms (
microbes
) that lived in the oceans; there were no animals
or plants. Carbon dioxide and methane concentrations were very high, and oxygen was
virtually absent. For most of the life on the planet, oxygen was poison. Some of Earthâs
early microbes began harvesting energy from the sun through photosynthesis, however,
and eventually became capable of splitting water molecules, which released oxygen as a
by-product. Bubble by bubble, these tiny organisms began gradually filling the atmosphere
with oxygen. By approximately 650 million years ago, the atmosphere contained enough
oxygen to sustain complex, multicellular life as we know it today.
Although those larger life forms tend to attract the most attention, microbes are by far
the most abundant and diverse form of life and have remained the engine behind all life
on Earth, maintaining the atmospheric and chemical conditions necessary for the survival
of all larger life forms. In fact, all multicellular forms of life are themselves inhabited by
microbes. These tiny beings make our world habitable; human beings are but guests in
their universe.
Humans are inextricably linked with the microbial communities that surround and sup-
port us. Many basic bodily processes depend on the trillions of microbes that colonize the
UNDERSTANDING OUR MICROBIAL PLANET
UNDERSTANDING OUR MICROBIAL PLANET
human body beginning shortly after birth. The vast majority of the microbes that live in
our bodies are not harmfulâmany, in fact, provide such essential functions as helping us
digest food, break down toxins, and fight off other, disease-causing microbes.
What we can learn from the microbes that sustain our planet and our bodies stretches the
limits of imagination. New scientific advances have enabled the scientific community to
uncover even further the possibilities that lie within microbial communities. This book-
let describes
metagenomics
, an emerging field that will revolutionize our understanding of
the microbial world and could lead to practical applications in areas including medicine,
energy, agriculture, biotechnology, and many others.
UNDERSTANDING OUR MICROBIAL PLANET
What we can learn from the microbes that sustain our planet and our
bodies stretches the limits of imagination.
UNDERSTANDING OUR MICROBIAL PLANET
WINDOW TO THE MICROBIAL
UNIvERSE: THE NEW SCIENCE
OF METAGENOMICS
W
hen Antony van Leeuwenhoek peered into his primitive 17th-
century microscope and discovered the single-celled organisms now
called microbes, he sparked a wave of scientific exploration of the
infinitely complex microbial world that would inspire scientists
for hundreds of years to come. Over the centuries, scientists
engaged in the study of microscopic organismsâcalled
microbiology
âdevised ever
more powerful ways of observing and understanding microbes. The new science
of metagenomics represents a quantum leap forward in microbiology analogous
to the revolutionary new view offered by that first microscope, and it provides
new insights into a previously inaccessible living universe.
What Is MetagenoMIcs
?
Metagenomics is an emerging field in which the power of genomic analysis
(the analysis of all the DNA in an organism) is applied to entire communities of
microbes, bypassing the need to isolate and culture individual microbial species.
In Greek,
meta
means âtranscendent.â In its approach and methods, metagenom-
ics transcends individual genes and genomes, enabling scientists to study all of the
genomes in a community as a whole.
The tools of classical genomics and microbiology largely rely on isolating individual
microbial species in pure culturesâthat is, cultures containing only microbes of a particular
UNDERSTANDING OUR MICROBIAL PLANET
species. This means that the vast majority of the microbial world has been inaccessible to
science because merely a miniscule fractionâmost scientists estimate less than 1%âof the
estimated millions of microbial species on Earth can be cultured. By allowing scientists to
access a communityâs genome without relying on pure cultures, metagenomics transcends
the limitations of classical genomics and microbiology.
Of course, metagenomics does not displace the need to study the genetic makeup of
individual species or small groups of microbes using the techniques of classical genomics
and microbiology. However, in the coming decades, the approaches of metagenomics will
likely merge with the approaches of those classical branches of science, greatly increasing
the potency of our understanding of the microbial world.
E x p l o r i n g M i c r o b E s
Early microscopes
reveal microbes
(1670s)
First taxonomy
of bacteria
(1872)
Culturing tech-
niques developed
(1880s)
Discovery of
viruses (1892)
Discovery of
antibiotics
(1928)
Discovery
of archaea
(1977)
E x p l o r i n g g E n E t i c s
Darwinâs Theory of
Evolution (1859)
Mendelâs work on
heredity (1866)
Structure
of DNA
determined
(1953)
Development
of sequencing
method
(1977)
First complete
bacterial genome
sequenced (1995)
Notable MoMeNts iN Microbiology
MEtagEnoMics
(1990s)
Since the discovery of microbial cells in the 17th century, scientific advancements have
opened many new windows to the microbial world. Culturing microbes in the laboratory
enabled scientists to explore a limited number of microbial species, and microbiology has
enabled major medical advances such as the development of vaccines and antibiotics.
Scientists began to understand DNA and the genetic mechanisms that drive living beings
and evolution, and the field of genomics, which emerged in the 1980s and '90s,
enabled scientists to identify all of the genes in an organism and to study those genes
either as an entire system or as isolated parts. The new field of metagenomics draws
from and transcends the advances that have been made in microbiology, genomics,
and other fields, opening up a multitude of new ways to explore the microbial world.
Metagenomics transcends individual genes and genomes, enabling scientists to study the
entire genetic makeup of a community as a whole. It is the science of microbial communities.
Understanding OUr MicrObial Planet
How Does MetagenoMics work
?
Metagenomics includes a wide variety of novel techniques and approaches, and it is likely
that other new methods will arise as the field progresses. currently, many metagenomics
studies take the same first step: researchers retrieve a sample from a particular environ-
ment (such as soil, seawater, or the human mouth) and do a mass extraction of the dna
from all the microbes in the sample. increasingly, scientists are also extracting protein or
rna from the microbes in a sample. Most metagenomics projects currently focus on the
microbes found in the sampled environment that have smaller amounts of dna, such
as bacteria and microbes known as archaea, which were identified as a major division of
organisms in 1977 and can live in extreme environments like deep sea vents, as well as a
variety of other habitats (see box 1).
typically, once the dna is extracted from a sample, laboratory bacteria are induced to take
up and replicate the dna, thus creating a âlibraryâ that contains pieces of the genomes of
all the microbes in the sample. (new sequencing technologies, however, facilitate sequenc-
ing dna directly from a sample, which streamlines the process by bypassing the creation
of a library.) a metagenomic library is not organized into neat volumes, however, each
containing the genome of one species; instead, this library consists of millions of random
fragments of dna from all the microbes in the sampled community.
BOX 1
.
Microbes
are living organisms too small to seeâgenerally smaller
than about 0.2 mm. The term includes Bacteria, Archaea, viruses, and small
Eukaryotes. Currently, most metagenomics projects exclude eukaryotes
because their genomes contain so much DNA that their genes would
overwhelm a metagenomic analysis, but eukaryotes will likely be
included in the future as the field develops new techniques.
Archaea. (Image from NOAA)
Bacteria. (Image from Pacific Northwest
National Laboratory)
Eukaryote. (Image from Nils Kroeger,
Georgia Institute of Technology)
UNDERSTANDING OUR MICROBIAL PLANET
What scientists do with a library of genomes, or
metagenome
, depends on what they want
to find out. In
sequence-based metagenomics, researchers focus on finding the entire
genetic sequence
âthe pattern of the four different nucleotide bases (A, C, G, and T) in the
DNA strandsâfound in a sample. The sequence can then be analyzed in many different
ways. For example, researchers can use a communityâs sequence to determine the complete
genome of an individual microbial species. Or, researchers might use the sequence to ana-
lyze the genome of the community as a whole, which can offer insights about population
ecology and evolution.
Function-based metagenomics explores the products that microbes in a community can
produce. In function-based metagenomics, researchers screen metagenomic libraries for
various functions, such as vitamin or antibiotic production. Through this method, scientists
can identify functions that are unknown in the limited number of microbes that can be
grown in a laboratory. New antibiotics have already been discovered using this approach.
Another approach to function-based metagenomics, made possible by recent technological
advances, enables scientists to directly extract and identify novel proteins and metabolites
(the products of cellular processes) from a microbial community.
extract all DNa from
microbial community in
sampled environment
DeterMiNe WHat tHe geNes are
(sequence-based metagenomics)
n
Identify genes and metabolic pathways
n
Compare to other communities
n
and moreâŚ
DeterMiNe WHat tHe geNes Do
(Function-based metagenomics)
n
Screen to identify functions of interest, such as
vitamin or antibiotic production
n
Find the genes that code for functions of interest
n
and moreâŚ
tHe MetageNoMics Process
UNDERSTANDING OUR MICROBIAL PLANET
APPLICATIONS:
WHAT METAGENOMICS CAN DO
T
he possibilities this new field offers are mind-boggling. Deciphering the
enormous array of processes and interactions that characterize microbial
communities on Earth can lead to advances in human health, improved
understanding of large-scale climatic and atmospheric changes, methods for
growing stronger and more nutritious crops, new approaches to cleaning up
environmental contamination, and new sources of renewable energy. These are just a few
examples of the many potential practical applications of metagenomics.
the WorlD WIthIn: learnIng FroM the MIcrobIal
InhabItants oF the huMan boDy
Humans always lived in a world dominated by microbes, and close relationships between
microbes and humans are an ancient theme. The microbes that reside on and in the adult
human body outnumber human cells by an estimated tenfold. (Nevertheless, human cells
still make up the bulk of our weight because resident microbes are much smaller than
human cells and collectively weigh only about two pounds.) The genomes of the microbial
communities living on and within the human body (the
human microbiome
) contain many
more genes than the human genome. Studying the human microbiome may lead to valuable
new tools and guidelines in human and animal nutrition, drug discovery, and preventative
medicine. Such study may also greatly expand the depth of our understanding of complex
diseases including obesity, cancer, and certain immune disorders, such as asthma.
Bacteria in human saliva. Trillions
of bacteria make up the normal
microbial community found in
and on the human body. (Image
from Michael Abbey)
UNDERSTANDING OUR MICROBIAL PLANET
10
UNDERSTANDING OUR MICROBIAL PLANET
The vast majority of our microbial partners live in the intestine. These
10 to 100 trillion microorganisms perform functions such as extract-
ing nutrients and calories from otherwise indigestible components of
our diets and making essential vitamins and amino acids. Some gut
bacteria also help detoxify potentially harmful chemicals contained in
what we eat. Some of the microbes living in and on the human body
play a critical role in defending us against pathogens. This mutually
beneficial relationship helps protect us from getting diseases while giv-
ing the microbes a place to live. Using metagenomics to gain a deeper
understanding of the microbial communities in and on the human body
could be immensely valuable in our understanding of both beneficial and
harmful microbes and may lead to more effective ways to diagnose, treat, and
possibly prevent disease.
The microbial world also offers a stunning array of biologically-active chemicals that
bacteria have evolved through communicating with and competing against each other
over billions of years. Bacteria are natureâs master chemists; a nearly endless variety of
powerful compounds can be derived from microbial communities. Hundreds of drugs
available today were derived from compounds scientists originally found in microbes.
Using metagenomics to study microbial communities may help us identify many more
new compounds that will promote the health of humans, animals, and plants throughout
the 21st century.
Bacteria are natureâs master chemists; a nearly endless variety of
powerful compounds can be derived from microbial communities.
gut MicrobEs and obEsity
Metagenomics studies can help researchers learn
about common diseases like obesity. Recently,
metagenomics was used to compare the genes in
the microbial communities in the guts of
obese mice with their leaner rela-
tives. The results suggested that
obesity is associated with
a shift in the proportions
of the two major groups
of gut bacteria. When
researchers transplanted
gut microbial communities
harvested from both obese
and lean animals into lean
germ-free mice, those that
received gut microbes from the
obese mice gained more fat. The take home
lesson: the caloric value of the food we eat
may vary depending upon the composition
of a person's gut microbes. Differences
in our gut microbial communities may
be one of many factors that affect
predisposition to obesity.
11
UNDERSTANDING OUR MICROBIAL PLANET
global IMpacts: the role
oF MIcrobes In MaIntaInIng
atMospherIc balances
It may seem surprising to learn that bacteria are responsible for about half the photosyn-
thesis on Earth. Most photosynthetic bacteria can be found freely swimming in the
oceans that cover 70% of the Earthâs surface. These bacteria affect key chemical
balances in the Earthâs atmosphere and play a crucial role in maintaining the
habitability of the entire planet.
One of the most important ways photosynthetic bacteria affect life on
Earth is through their role in the global carbon cycle. Carbon is the
most abundant element in living things, including humans (excluding
the hydrogen and oxygen in the water that makes up the bulk of our
weight). However, most of the carbon on Earth is in the form of
carbon dioxide (CO
2
), which cannot be used by animals and most
bacteria. Through photosynthesis, plants and certain bacteria âfixâ
carbon from the atmosphere, turning it into a form that is useable to
many more life forms (and releasing oxygen). Through the process
of fixing carbon, photosynthetic bacteria remove CO
2
âwhich is a
major greenhouse gasâfrom the atmosphere. In this way, photosyn-
thetic bacteria mitigate some of the effects of the release of CO
2
and
other greenhouse gases from human activities that most scientists believe
is responsible for global warming.
To achieve complex chemical transformations, no single microbe can do it alone;
it takes a community. Many microbial communities, including those involved in the
generation and consumption of greenhouse gases, function through a âbucket brigadeâ
system, in which each microbe performs its own individual task, with its end product
becoming the starting fuel for its neighbor. Through metagenomics, scientists can exam-
ine the genetic bases behind these complex bucket brigades and explore how genes from
various organisms influence each otherâs activities.
To achieve complex chemical transformations, no single
microbe can do it alone; it takes a community.
Photosynthetic bacteria living in
the sea have a major impact on
the Earthâs atmospheric balances.
(Image from NASA)
1
UNDERSTANDING OUR MICROBIAL PLANET
Metagenomics can help scientists gain insights into the mechanisms behind changes of
energy and matter in the sea, the composition of Earthâs atmosphere, and global climate.
bIoenergy: harnessIng MIcrobIal poWer
There is a growing awareness that the worldâs reliance on energy from nonrenewable fossil
fuels is not sustainable. It is projected that U.S. energy demand will increase by more than
50% by 2025, and our dependence on
fossil fuels puts us at risk of disturbances
in energy supply due to changing politi-
cal climates and international relations.
Additionally, the greenhouse gas emis-
sions that result from burning fossil fuels
are widely believed to be a primary cause
of global warming. All of these factors
make finding renewable, environmentally friendly fuels a
major priority for Americaâand the world.
One emerging energy source is ethanol (grain alcohol)âa
high-octane biofuel derived from corn, sugarcane, or other
agricultural sources.
Cellulosic
ethanol
is made from the cellu-
lose found in such common agricultural wastes as corn fiber,
corn stalks, wheat straw, and other biomass like switchgrass
and miscanthus. But the process that converts the cellulose
from agricultural waste into usable ethanol depends on one
essential ingredient: microbial communities. First, several
types of microorganisms must work in concert to transform
the cellulose from agricultural wastes into sugars. Then,
the sugars are fermentedâalso by microbesâto produce
ethanol.
The process that converts the cellulose from
agricultural waste into usable ethanol (grain
alcohol) depends on one essential ingredient:
microbial communities.
1
UNDERSTANDING OUR MICROBIAL PLANET
Still other microbes produce a variety of potential energy sources including hydrogen,
methane, butanol, and even electric current. By carefully manipulating the availability
of nutrients and other environmental conditions, scientists are working to develop ways
to capture and store the useful by-products of such microbes. But much more needs to
be known about how these microbial communities function before we can control and
channel the energy sources they produce. Metagenomics offers an important means of
achieving this knowledge and should be considered a part of Americaâs strategic approach
to addressing present and future needs for renewable energy sources.
sMart FarMIng: hoW MIcrobes help our crops
One of the most valuable but least understood mysteries of farming is the âsuppressive
soilâ phenomenon. In suppressive soils, plants stay healthy even when disease-causing
organisms are present in high densities. If this soil is sterilized, killing helpful and harmful
microbes alike, plants can become sick and die once the pathogens find their way back
into the soil. Scientists speculate that microbes living in the suppressive soil actually pro-
tect plants from diseasesâand if these microbes disappear, plants are far more susceptible
to infection. Despite decades of research, scientists have only been able to pinpoint the
microbes responsible for suppressing disease in a few locations. Scientists believe that a
complex microbial community is responsible for suppressing disease, because no single
microbial species can do it alone. The activities of suppressive soil communities are enor-
mously beneficial to agriculture.
The microbial communities on and around plants are also critical to manufacturing the
nutrients that plants need in order to grow. Certain bacteria convert atmospheric nitrogen
into ammonia, a form that is readily usable by plants and animals. Other soil microbes
recycle nutrients from decaying plants and animals, while still others convert elements,
such as iron and manganese, to forms that can be used for plant nutrition. Once again,
it takes a community to perform these critical biotransformations. For example, no one
microbe is capable of converting ammonia to nitrate, yet teams of microbes do this very
efficiently.
Starter microbes are added to a
bioreactor to convert agricultural
material into ethanol. (Image from
USDA; photo by Keith Weller)
Complex microbial communities
living in soil provide essential
nutrients and help protect plants
from diseases.
1
UNDERSTANDING OUR MICROBIAL PLANET
While scientists have been able
to glimpse the complex microbial
communities that help keep crops
healthy and productive, much about
those communities remains mysteri-
ous. Metagenomics offers a unique
opportunity to explore how micro-
bial communities interact with crops
and may eventually lead to ways to
harness the power of soil microbial
communities to produce healthier
and more robust crops.
cleanIng up: reMeDIatIon oF
envIronMental contaMInatIon
Microbial communities are crucial participants in cleaning up an astounding variety of
both natural and human-made hazardous substances; they transform potentially deadly
chemicals into forms that are benign both to people and to the environment. Some
microbes consume methane gasâa major greenhouse gasâwhich seeps from landfills and
swamps. Other microbes degrade the waste in sewage water at water treatment facilities.
Communities of marine bacteria, similar to the soil microbes that degrade gasoline leaks
on land, can help clean up oil spills in the Earthâs oceans.
While we know that microbial communities are immensely useful in degrading waste
and hazardous spills, our understanding of the processes involvedâand how to channel
Metagenomics can facilitate the
development of farming practices
that take advantage of the natu-
ral alliances among microbes and
plants and animals. (Image from
James Tiedje)
Microbial communities transform many potentially deadly chemicals into forms
that are benign both to people and to the environment.
1
UNDERSTANDING OUR MICROBIAL PLANET
those processes to manage the fast-
growing array of chemicals humans
put into the environmentâis as
yet limited. Metagenomic analysis
may help us identify the particular
community members and functions
needed to achieve the full chemical
transformations that will keep our
planet livable.
KEEping groundwatEr drinKablE
Just about every gas station in the United States has three or more underground storage tanks from which it dis-
penses gasoline. The sad truth about these tanks is that many of them are either currently leaking or will leak at
some time in the future, releasing gasoline into the soil, where it has the potential to contaminate groundwater.
Given the ubiquity and magnitude of the gasoline leaksâcoupled with the fact that 50% of the U.S. population
relies on groundwater as a source of drinking waterâone must wonder how we are not all drinking water con-
taminated with gasoline!
The answer is that we are often protected by the vastly adaptable microbial community found in the soil. As
gasoline is released into the ground, relatively dormant members of the soil microbial community are triggered
to become active and degrade the harmful chemicals in gasoline. Because gasoline is composed of hundreds of
chemicals, it takes a variety of microbes working together to degrade them all. For example, when some types of
bacteria cause a depletion of oxygen in the groundwater near a gasoline spill, other types of bacteria that can use
nitrate for energy begin biodegrading the gasoline. Bacteria that use iron, manganese, and sulfate follow. These
community members work together in a pattern triggered by the movement of the leaking gasoline until the con-
taminants have been transformed into harmless carbon dioxide and water.
Marine microbes can help to degrade hazardous oil
spills in the ocean. (Image from NOAA HAzMAT)
1
UNDERSTANDING OUR MICROBIAL PLANET
Microbes can break down gasoline leaking from underground
storage tanks at gas stations.
1
UNDERSTANDING OUR MICROBIAL PLANET
GETTING THE MOST OUT OF NEW
SCIENTIFIC ADvANCES
M
aking full use of the powerful new tools provided by metagenomics
and other new scientific advances is not without its challenges. The
2007 National Research Council report
The New Science of Metagenomics:
Revealing the Secrets of Our Microbial Planet
addresses the challenges and
opportunities metagenomics holds for the future of microbiology. The
report describes a number of technological, methodological, and computational advances
that are needed before metagenomics can reach its full potential.
challenges to MetagenoMIcs MethoDs.
There is an enormous amount of work
to be done establishing the foundations, defining standard practices, and building the frame-
work to support the field. Many stages of a metagenomics project remain challenging:
⢠Getting a good sample from an environment is an essential, but difficult, step. Scientists
must determine the best way to sample an environment, how many times samples should
be taken, and whether a sample is representative of the environment.
⢠Better DNA extraction techniques are needed. Detecting the rare members of a micro-
bial community is a challenge, but it can be very important if a small number of microbes
play a critical role in the community. Improved DNA extraction techniques could help
ensure that a metagenomic library adequately represents the entire communityâs genome
and has little or no contamination.
⢠Extending the analyses beyond the DNA sequence to study the proteins and metabolites
(the products of cellular processes) generated by a community will be critical for under-
standing how a given microbial community operates and interacts with its habitat.
1
UNDERSTANDING OUR MICROBIAL PLANET
Data ManageMent anD bIoInForMatIcs neeDs.
Metagenomics projects gener-
ate enormous amounts of data, and effective data management systems will be essential for
advancing the field. New databases with the following
characteristics are needed:
⢠Data generated from metagenomics projects
should be stored in databases that are freely
accessible to all.
⢠Metagenomics databases should use
common standards. Not only sequence
data but also information on sampling
methods, sample treatments, and sam-
pled habitats should be recorded.
⢠Databases should include specialized
tools that enable different scientists to
analyze the data in different ways. This will
ensure that data stored in the databases will
be of increasing, rather than diminishing, value as
technology advances.
organIzatIonal anD InstItutIonal FraMeWorks.
Metagenomics will benefit
from the involvement of experts from a broad range of fields; included among these should
be chemistry, genetics, microbiology, biochemistry, pathology, ecology, evolution, soil and
atmospheric sciences, geology, oceanography, statistics, computer sciences, database devel-
opment, mathematics, engineering, and others. Universities will need to rapidly evolve their
educational, administrative, and mentoring structures to facilitate interdisciplinary collabo-
ration to help metagenomics reach its full potential.
Because of the broad scope of metagenomics, this new field is of potential value in fulfill-
ing the missions of several federal agencies, including the National Science Foundation,
the National Institutes of Health, the Department of Energy, state agencies, and others.
1
UNDERSTANDING OUR MICROBIAL PLANET
Communication and coordination across the relevant agencies would be extremely useful
in advancing the field.
establIshIng a âglobal MetagenoMIcs InItIatIve.â
The New Science of Metagenomics:
Revealing the Secrets of Our Microbial Planet
recommends that a Global Metagenomics
Initiative be established in the United States that would include a small number of large-
scale, comprehensive projects, a larger number of medium-sized projects, and many small-
scale projects.
⢠Large-scale projects will each explore a microbial community in great depth, analyzing a
habitat with attention to potential for discovery, variation, commonalities, and detailed
investigation. Possible candidate communities include:
â˘
a community in a natural environment (such as seawater or soil),
â˘
a host-associated community (such as the microbes in the human gut or mouth), and
â˘
a âmanagedâ environment community (such as a sewage treatment facility or bioreme-
diation site).
⢠Medium-sized projects will encompass the greater diversity of microbial habitat types. Such
projects should include a multidisciplinary approach to the study of microbial communities.
⢠Small-scale projects will be initiated by individual scientists to examine a slice of a com-
munity, a particular function in multiple communities, or a specific technical advance.
1
UNDERSTANDING OUR MICROBIAL PLANET
SUMMARy
H
umans might conceivably survive in a world lacking other large life
forms, but without microbes all complex plants and animalsâincluding
ourselvesâwould likely die. It is microbes that convert key elements
of lifeâsuch as carbon, nitrogen, and sulfurâinto forms accessible to
all other living things. Traditional microbiological approaches have
already shown how useful microbes can be; the new approach of metagenomics will
greatly expand our ability to discover and benefit from the incredible capabilities of the
microbial world.
Metagenomics provides a new lens for viewing the microbial world that has the potential
to revolutionize understanding of the entire living world. In metagenomics, the power
of genomic analysis is applied to entire communities of microbes, bypassing the need to
isolate and culture individual microbial species. This new approach will bring to light the
many abilities of the microbial communities that drive Earthâs energy and nutrient cycles
and support the health of its inhabitants. Metagenomics will vastly enhance our knowl-
edge of microbial communities and can lead to major advancements in many areas, includ-
ing human health, agriculture, energy production, and environmental remediation.
Without microbes all complex plants and animalsâ
including ourselvesâwould likely die.
0
UNDERSTANDING OUR MICROBIAL PLANET
MICROBIAL COMMUNITIES
support all
life on Earth;
metagenomics
is a revolutionary
new approach to understanding the charac-
teristics of our microbial world. This new
science opens doors to a tremendous amount
of scientific exploration and can help address
some of the most complex medical, environ-
mental, agricultural, and economic challenges
of todayâs world.
a New TooL foR ScieNTific
eXPLoRaTioNâŚ
MeDiciNe:
Examining how the microbial communities
that normally inhabit our bodies affect human health can
lead to new strategies for diagnosing, treating, and pos-
sibly preventing diseases.
Life ScieNceS:
deciphering how microbial communi-
ties function can partially answer fundamental questions
about microbial, plant, and animal biology and greatly
enhance our understanding of ecology and evolution.
eaRTh ScieNceS:
Exploring how microbial communi-
ties in the soil and in the ocean affect atmospheric
balances and environmental conditions can help us under-
stand, predict, and potentially address global changes.
aBoUT The NaTioNaL acaDeMieS
The national academiesâthe national academy of sciences, national academy of
Engineering, Institute of Medicine, and the national research councilâprovide a
public service by working outside the framework of government to ensure independent
advice on matters of science, technology, and medicine. They enlist committees of
the nation's top scientists, engineers, and other expertsâall of whom volunteer their
time to study specific concerns. The results of these deliberations are authoritative,
peer-reviewed reports that have inspired some of the nationâs most significant efforts to
improve the health, education, and welfare of the population.
This booklet was derived from the national research council report
The New Science of
Metagenomics: Revealing the Secrets of Our Microbial Planet
(2007) by the committee on
Metagenomics: challenges and Funcitonal applications.
http://books.nap.edu/catalog.
php?record_id=11902
coMMiTTee oN MeTageNoMicS: chaLLeNgeS aND fUNcTioNaL aPPLicaTioNS
Jo handelsman (co-chair), University of Wisconsin-Madison; James M. Tiedje (co-
chair), Michigan state University;
Lisa alvarez-cohen, University of california,
berkeley;
Michael ashburner, University of cambridge; isaac K. o. cann, University
of Illinois, Urbana-champaign;
edward f. DeLong, Massachusetts Institute of
Technology;
w. ford Doolittle, dalhousie University; claire M. fraser-Liggett,
The Institute for genomic research;
adam godzik, The burnham Institute; Jeffrey i.
gordon, Washington University school of Medicine; Margaret Riley, University of
Massachusetts, amherst;
Molly B. Schmid, Keck graduate Institute; ann h. Reid (study
director), national research council.
reports from the national academies are available from the national academies Press,
500 Fifth street, nW, Washington, dc 20001; 800-624-6242;
http://www.nap.edu.
reports are available online in a fully searchable format.
This booklet and related materials are available at
http://dels.nas.edu/metagenomics.
This publication was written by anne Jurkowski and ann reid and was designed by
Van nguyen. cover art by nicolle rager Fuller (
www.sayo-art.com); page 3 watermark
image from U.s. department of Energy; page 17 photo by Jeff Miller, University of
Wisconsin-Madison.
copyright 2007 by the national academy of sciences. all rights reserved.
heLPiNg aDDReSS The chaLLeNgeS
of ToDaYâS woRLDâŚ
aLTeRNaTiVe eNeRgY:
Harnessing the power of
microbial communities may lead to more sustainable
and environmentally friendly biologically-based ener-
gy sources.
eNViRoNMeNTaL ReMeDiaTioN:
developing
microbe-based tools for monitoring environmental
damage and cleaning up oil spills, groundwater, sew-
age, nuclear waste, and other hazards may help restore
healthy ecosystems.
BioTechNoLogY:
Taking advantage of the
diverse abilities of microbial communities may lead
to the development of beneficial industrial, food, and
health products.
agRicULTURe:
gaining a better understanding of
the beneficial microbes living in, on, and around do-
mestic plants and animals can contribute to improved
methods for detecting diseases in crops, livestock, and
food products and can facilitate the development of
farming practices that take advantage of the natural
alliances among microbes and plants and animals.
BioDefeNSe aND MicRoBiaL foReNSicS:
studying the dna and biochemical fingerprints of
microbial communities helps specialists monitor known
and potential pathogens, create more effective vaccines
and treatments against potential bioterror agents, and
reconstruct events in which microbes have played a role.
NatioNal academy of ScieNceS NatioNal academy of eNgiNeeriNg iNStitute of mediciNe NatioNal reSearch couNcil
H
umankind has benefited enormously from the study of microbes since their
discovery in the 17th century. However, such benefits have come from
the study of just a miniscule fraction of the millions of species of microbes
in the environment. In addition, scientists are realizing the importance
of studying the collective properties of communities of microbes, which perform com-
plex tasks essential to the health of human beings and our planet. The emerging field of
metagenomics opens the door to exploring the vast array of microbes unstudied to date
and to investigating entire microbial communities. Through a deeper understanding of the
microbes that sustain life on Earth, the metagenomics approach offers the promise of an
incredible array of new benefits.
U n d E r s T a n d I n g O U r
MIcrObIal PlanET
T h e N e w S c i e N c e o f M e T a g e N o M i c S