The Promise and Perils
of Synthetic Biology

Jonathan B. Tucker and Raymond A.
Zilinskas

ver the past fifty
years, several pivotal advances have transformed the
life sciences, including the discovery of the structure
of DNA, the deciphering of the genetic code, the
development of recombinant DNA technology, and the
mapping of the human genome. Synthetic biology is
another transformative innovation that will make it
possible to build living machines from off-the-shelf
chemical ingredients, employing many of the same
strategies that electrical engineers use to make
computer chips. Drawing upon a set of powerful
techniques for the automated synthesis of DNA molecules
and their assembly into genes and microbial genomes,
synthetic biology envisions the redesign of natural
biological systems for greater efficiency, as well as
the construction of functional “genetic circuits” and
metabolic pathways for practical purposes.

Among the potential applications of this new field is
the creation of bioengineered microorganisms (and
possibly other life forms) that can produce
pharmaceuticals, detect toxic chemicals, break down
pollutants, repair defective genes, destroy cancer
cells, and generate hydrogen for the post-petroleum
economy. Although synthetic biology is chiefly an
engineering discipline, the ability to design and
construct simplified biological systems offers life
scientists a useful way to test their understanding of
the complex functional networks of genes and
biomolecules that mediate life processes.

Today, synthetic biology is at roughly the same level
of development as molecular genetics was in the mid- to
late 1970s, some five years after the invention of
recombinant-DNA technology. In June 2004, the first
international conference devoted to the new field,
“Synthetic Biology 1.0,” was held at the Massachusetts
Institute of Technology (M.I.T.). The organizers claimed
to have “brought together, for the first time,
researchers who are working to: (1) design and build
biological parts, devices, and integrated biological
systems, (2) develop technologies that enable such work,
and (3) place this scientific and engineering research
within its current and future social context.” In
addition to technical presentations, policy analysts
addressed the security, safety, and ethical issues
associated with synthetic biology. The second
international conference, “Synthetic Biology 2.0,” is
scheduled for May 20-22, 2006, at the University of
California, Berkeley. Meanwhile, at M.I.T. and several
other universities, synthetic biology has become a
powerful catalyst for interdisciplinary research and
teaching that bridges the life sciences and engineering,
attracting the interest of undergraduates, graduate
students, and faculty members from a wide variety of
fields.

Many of the enabling technologies for synthetic
biology have existed for several years. The metabolic
engineering of bacteria for natural product synthesis
was first achieved in the early 1970s, and engineered
bacterial plasmids for biotechnology were developed
during the 1980s. Genetically modified organisms with
relatively sophisticated systems for gene expression and
containment have been around for nearly as long. The
main difference between genetic engineering and
synthetic biology is that whereas the former involves
the transfer of individual genes from one species to
another, the latter envisions the assembly of novel
microbial genomes from a set of standardized genetic
parts. These components may be natural genes that are
being applied for a new purpose, natural genes that have
been redesigned to function more efficiently, or
artificial genes that have been designed and synthesized
from scratch.

Although much of the current work on synthetic
biology is taking place in the United States, research
groups are also active in Europe, Israel, and Japan, and
the technology will surely spread to other countries.
Over the next decade, synthetic biology is likely to
enter a phase of exponential growth. Already, leading
U.S. practitioners have founded three private companies
to commercialize the technology: Codon Devices of
Cambridge, Massachusetts; Amyris Biotechnologies of
Emeryville, California; and Synthetic Genomics of
Rockville, Maryland.

If the history of molecular biology is any guide,
synthetic biology research will generate a vast amount
of new information about life processes—from the role of
specific genes to the metabolism of whole organisms—as
well as numerous applications in medicine, agriculture,
industry, bioremediation, and energy. And as with any
powerful new technology, synthetic biology is likely to
create new risks for society, including possible
unintended harmful consequences for human health or the
environment, or deliberate misuse for hostile purposes.
To gauge and plan for those risks, we need to understand
the current status of research and the possible
directions of future developments in the field.

Surveying Synthetic
Biology

Today, synthetic biology
encompasses several different engineering strategies,
including genome design and construction, applied
protein design, natural product synthesis, and the
construction of functional genetic circuits in cells and
microorganisms. Each of these subfields is worth
considering briefly.

Genome Design and Construction. One
goal of synthetic biology is to “redesign” the genomes
of existing microbes to make them more efficient or
program them to carry out new functions. In 2005, for
example, Leon Y. Chan and his co-workers at M.I.T.
simplified the genome of a bacteriophage (a virus that
attacks bacteria but is harmless to humans) called T7 by
separating overlapping genes and editing out redundant
DNA sequences to facilitate future modifications. In
addition, a group at the J. Craig Venter Institute in
Rockville, Maryland is currently redesigning the
bacterium Mycoplasma genitalium, which has the
smallest known bacterial genome (482 protein-coding
genes, 43 RNA genes) yet possesses all of the
biochemical machinery needed to metabolize, grow, and
reproduce. The Venter Institute group is striving to
develop a synthetic version of the M. genitalium
genome that has been stripped down to the absolute
minimum number of genes required to support independent
life. The goal of this “minimum genome project” is to
build a simplified microbial platform to which new genes
can be added, creating synthetic organisms with known
characteristics and functionality.

“Synthetic genomics” refers to the set of
technologies that makes it possible to construct any
specified gene (or full genome) from short strands of
synthetic DNA called “oligonucleotides,” which are
produced chemically and are generally between 50 and 100
base-pairs in length. In August 2002, Eckard Wimmer, a
virologist at the State University of New York at
Stonybrook, announced that over a period of several
months his research team had assembled live, infectious
poliovirus from customized oligonucleotides mail-ordered
from a commercial supplier, using a map of the viral
genome available on the Internet. In 2003, Hamilton
Smith and his colleagues at the Venter Institute
developed a faster method for genome assembly, using
synthetic oligonucleotides to construct a bacteriophage
called φX174 (containing 5,386 DNA base-pairs) in only
two weeks. Most recently, in 2005, scientists at the
U.S. Centers for Disease Control and Prevention
synthesized the so-called Spanish influenza virus which
was responsible for the 1918-19 flu pandemic that killed
between 50 million and 100 million people worldwide.

In the near future, synthetic genomics technology
should make it possible to recreate any existing virus
for which the complete DNA sequence is known. At the
same time, the advent of high-throughput DNA synthesis
machines will cause the associated costs to drop
precipitously, continuing the existing trend. In the
year 2000, the price of custom oligonucleotides was
about $10 per DNA base-pair; by early 2005, Blue Heron
Biotechnology of Bothell, Washington was charging only
$2 per base-pair (discounted to $1.60 for new
customers). Over the next five years, the cost of
synthetic DNA is expected to drop to about 10 cents per
base-pair or even less, according to a recent report
from the National Research Council and the Institute of
Medicine. In December 2004, George M. Church of Harvard
Medical School and Xiaolian Gio of the University of
Houston announced that they had invented a new
“multiplex” DNA synthesis technique that Church claims
will eventually reduce the cost of DNA synthesis to
20,000 base-pairs per dollar. If his prediction is borne
out, it will transform the economics of genome
synthesis.

Applied Protein Design. In the early
1980s, Kevin Ulmer of Genex Corporation conceived the
idea of systematically altering the genes that code for
certain proteins to achieve desired modifications in
protein stability and function. Since then,
protein-engineering technology has been applied to
develop enzymes that have improved catalytic efficiency
or altered substrate specificity, or that can tolerate
high temperatures and acidity levels. Today, engineered
enzymes are utilized in laundry detergents and in
various industrial processes. Another approach to
protein engineering involves going beyond the repertoire
of the 20 amino-acid building blocks found in nature.
For example, a team of chemists headed by Peter G.
Schultz at Lawrence Berkeley National Laboratory has
expanded the genetic code to specify unnatural amino
acids, which can be substituted into proteins to modify
their stability as well as their catalytic and binding
properties. This technique has made it possible to
design protein-based drugs that can resist rapid
degradation in the body.

Natural Product Synthesis.
Recombinant-DNA technology has long permitted the
replication of single genes in plasmids (small loops of
bacterial DNA), a technique known as “molecular
cloning,” followed by the expression of the encoded
proteins in bacteria or yeast cells. Useful proteins
such as human insulin can be produced cheaply with this
technique. Now, with the advent of synthetic biology,
scientists are engineering microbes to perform complex
multi-step syntheses of natural products by assembling
“cassettes” of animal or plant genes that code for all
of the enzymes in a synthetic pathway.

For example, Jay Keasling, a professor of chemical
engineering at the University of California, Berkeley,
is using synthetic-biology techniques to program yeast
cells to manufacture the immediate precursor of the drug
artemisinin, a natural product that is highly effective
in treating malaria. At present, this compound must be
extracted chemically from the sweet wormwood plant, an
annual indigenous to China and Vietnam. The extraction
of artemisinin is difficult and expensive, however,
reducing its availability and affordability in
developing countries. Keasling’s group is trying to
reduce the cost of the drug by engineering a metabolic
pathway for the synthesis of its immediate precursor,
artemisinic acid, in yeast.

Thus far, the Berkeley researchers have assembled a
cassette of several genes from sweet wormwood that code
for the series of enzymes needed to make artemisinic
acid, and inserted this cassette into baker’s yeast
(Saccharomyces cerevisiae). The scientists are
now “tuning” the expression levels of each gene so that
the entire multi-enzyme pathway functions efficiently.
This task is far more complex than traditional
experiments involving the cloning and expression of
individual genes. Once the engineered yeast cells have
been coaxed into producing high yields of the
artemisinin precursor, it should be possible to
manufacture this compound cheaply and in large
quantities by fermentation, a process similar to brewing
beer. The same approach could be used to mass-produce
other drugs that are currently available in limited
quantities from natural sources, such as the anti-cancer
drug taxol and the anti-HIV compound prostratin.

Creation of Standardized Biological Parts and
Circuits. Perhaps the most ambitious subfield of
synthetic biology involves efforts to develop a “tool
box” of standardized genetic parts with known
performance characteristics—analogous to the
transistors, capacitors, and resistors used in
electronic circuits—from which bioengineers can build
functional devices and, someday, synthetic
microorganisms.

The Synthetic Biology Working Group at M.I.T. is
attempting to turn this concept into a reality by
developing a comprehensive set of genetic building
blocks, along with standards for characterizing their
behavior and the conditions that support their use. In
the summer of 2004, the group established a Registry of
Standard Biological Parts. The registry is made up of
components called “BioBricks,” short pieces of DNA that
constitute or encode functional genetic elements.
Examples of BioBricks are a “promoter” sequence that
initiates the transcription of DNA into messenger RNA, a
“terminator” sequence that halts RNA transcription, a
“repressor” gene that encodes a protein that blocks the
transcription of another gene, a ribosome-binding site
that initiates protein synthesis, and a “reporter” gene
that encodes a fluorescent jellyfish protein, causing
cells to glow green when viewed through a fluorescence
microscope. A BioBrick must have a genetic structure
that enables it to send and receive standard biochemical
signals and to be cut and pasted into a linear sequence
of other BioBricks, in a manner analogous to the pieces
in a Lego set.

As of early April 2006, the BioBricks registry
contained 167 basic parts, including sensors, actuators,
input and output devices, and regulatory elements. Also
included in the registry were 421 composite parts, and
an additional 50 parts were being synthesized or
assembled. Emulating the approach employed by
open-source software developers, the M.I.T. group has
placed the registry on a public website (http://parts.mit.edu/) and invited all
interested researchers to comment on and contribute to
it. The ultimate goal of this effort is to develop a
methodology for the assembly of BioBricks into circuits
with practical applications, while eliminating
unintended or parasitic interactions that could
compromise the characterized function of the parts.

To date, BioBricks have been assembled into a few
simple genetic circuits. One such circuit renders a film
of bacteria sensitive to light, so that it can capture
an image like a photographic negative. In other
experiments, BioBricks have been combined into devices
that function as logic gates and perform simple Boolean
operations, such as AND, OR, NOT, NAND, and NOR. For
example, an AND operator generates an output signal when
it gets a biochemical signal from both of its inputs; an
OR operator generates a signal if it gets a signal from
either input; and a NOT operator (or inverter) converts
a weak signal into a strong one, and vice versa. The
long-term goal of this work is to convert bioengineered
cells into tiny programmable computers, so that it will
be possible to direct their operation by means of
chemical signals or light.

Research Obstacles and
Potential Risks

Although synthetic
biologists have accomplished a great deal in a short
time, major obstacles remain to be overcome before the
practical applications of the technology can be
realized. One problem is that the behavior of
bioengineered systems remains “noisy” and unpredictable.
Genetic circuits also tend to mutate rapidly and become
nonfunctional. Drew Endy of M.I.T., one of the pioneers
in the field, believes that synthetic biology will not
achieve its potential until scientists can predict
accurately how a new genetic circuit will behave inside
a living cell. He argues that the engineering of
biological systems remains expensive, unreliable, and ad
hoc because scientists do not understand the molecular
processes of cells well enough to manipulate them
reliably.

Writing in Nature in late 2005, Endy suggested
three strategies for overcoming these obstacles. The
first, standardization, refers to the
“promulgation of standards that support the definition,
description and characterization of the basic biological
parts, as well as standard conditions that support the
use of parts in combination and overall system
operation.” The M.I.T. Registry of Standard Biological
Parts is a first step toward that end. The second,
decoupling, is the effort to “separate a
complicated problem into many simpler problems that can
be worked on independently, such that the resulting work
can eventually be combined to produce a functioning
whole.” Finally, abstraction is a method for
organizing information describing biological functions
into “hierarchies” that operate at different levels of
complexity. Following these strategies, Endy writes,
“would help make routine the engineering of synthetic
biological systems that behave as expected.”

An assessment of the risks involved in synthetic
biology research must begin with two obvious points.
First, because engineered microorganisms are
self-replicating and capable of evolution, they belong
in a different risk category than toxic chemicals or
radioactive materials. Second, some of the risks of
synthetic biology are simply indefinable at present—that
is, there may be risks that we cannot anticipate with
any degree of precision at this early stage in the
development of the field.

That said, we can use history as a guide—particularly
the history of recombinant DNA technology—to discern
three main areas of risk in synthetic biology. First,
synthetic microorganisms might escape from a research
laboratory or containment facility, proliferate out of
control, and cause environmental damage or threaten
public health. Second, a synthetic microorganism
developed for some applied purpose might cause harmful
side effects after being deliberately released into the
open environment. Third, outlaw states, terrorist
organizations, or individuals might exploit synthetic
biology for hostile or malicious purposes.

The Risk of Accidental
Release

The history of the risks
and safeguards involved in recombinant DNA research,
which involves the cutting and splicing of genes from
different species, is instructive for understanding the
risks associated with synthetic biology. The first
people to voice concerns about the potential risks of
recombinant DNA research were the scientists doing the
work. During the summer of 1975, the leading
investigators in the field met at the Asilomar
Conference Center in Pacific Grove, California, to
discuss the hazards associated with the new technology.
They concluded that although most gene transfers posed a
low level of risk, a few types of experiments, such as
the insertion of toxin genes and virulence factors into
bacteria, could entail significant dangers. In response,
the National Institutes of Health (NIH) established a
Recombinant DNA Advisory Committee (RAC) to develop
biosafety guidelines and a process for institutional
oversight that would apply to all NIH-funded research
projects.

Under the NIH Guidelines, which were adopted in 1976,
the most dangerous experiments were banned and others
were subjected to a thorough risk assessment. The
guidelines specify the level of laboratory
biocontainment required for different types of
gene-transfer experiments. Many scientists considered
the NIH Guidelines overly restrictive when they were
first introduced, but over the past thirty years, the
guidelines have gradually evolved in response to
experience: Because of the excellent safety record of
gene-splicing research and development, the RAC has
since downgraded the biosafety requirements for most
types of recombinant DNA experiments.

Despite the fact that no accidental release of a
genetically-engineered microorganism (GEM) from a
laboratory has been reported, it is possible that such
releases have occurred but that the effects were so
unremarkable that they remained undetected. GEMs
generally appear to be less “fit” than their natural
counterparts and hence would probably die off rapidly in
the environment. Nevertheless, given their potential to
replicate and evolve, special precautions are warranted.
To reduce the probability that GEMs could proliferate
outside a containment facility, the NIH Guidelines
require that scientists build safeguards into the host
microbes that receive foreign DNA. For example,
researchers have developed bacterial strains that are
metabolically deficient and thus require special
nutrients that are not available in nature, so that the
bacteria can survive and propagate only under artificial
laboratory conditions.

The main lesson for synthetic biology from the
regulation of recombinant DNA research concerns the
extent of the researcher’s familiarity with the host
microbe that is being genetically modified. Because the
microorganisms used for genetic engineering, such as the
bacterium E. coli and the yeast S.
cerevisiae, are well understood by scientists, the
transfer of one or two foreign genes is unlikely to
change the characteristics of the host in a dramatic,
unpredictable way.

To what extent would the risks associated with a
synthetic microorganism differ from those of a
genetically engineered one? At least for the near
future, the vast majority of synthetic biological
systems will be engineered by transferring small genetic
circuits into a well-understood bacterial host, limiting
the level of risk. A decade from now, however, synthetic
genomes may be assembled from BioBricks that have been
redesigned or are entirely artificial, having been
created de novo. If a synthetic microorganism is
built by combining these genetic elements in a new way,
it will lack a clear genetic pedigree and could have
“emergent properties” arising from the complex
interactions of its constituent genes. Accordingly, the
risks attending the accidental release of such an
organism from the laboratory would be extremely
difficult to assess in advance, including its possible
spread into new ecological niches and the evolution of
novel and potentially harmful characteristics.

During the process of laboratory research, animal
testing in a contained facility may suggest whether or
not a synthetic microorganism is pathogenic.
Nevertheless, no animal model can predict infallibly how
a novel microbe will behave in a human host, and there
is no reliable way to measure its possible impact on
complex ecosystems. It is also unclear whether or not
the standard techniques used to prevent GEMs from
proliferating outside the laboratory will be effective
for synthetic microbes. As a result, future research
involving the creation of synthetic microorganisms will
pose major challenges for assessing and managing
biosafety risks. It is not too early to begin thinking
about this problem, which is likely to be quite
difficult to solve.

To the extent that synthetic microorganisms lack a
natural genetic pedigree, regulators may insist on
developing new biosafety guidelines or regulations to
prevent their accidental release into the environment.
At present, it is unclear if these rules would resemble
the NIH Guidelines or would be specific to synthetic
biology. One approach to reducing the possible risks
associated with synthetic microorganisms would be to
ensure that they are inherently incapable of surviving
and replicating outside the laboratory. For example,
synthetic bacteria might be endowed with a redesigned
genetic code and unnatural amino acids so that even if
the engineered genes were taken up by natural cells or
viruses, they could not be expressed. Scientists may
also build into a synthetic microbe a “self-destruct”
mechanism that is triggered by a high density of
microorganisms, a specified number of cell divisions, or
an external chemical signal. Nevertheless, such built-in
control mechanisms may not be foolproof. If, for
example, a synthetic microorganism is accidentally
released into the environment, it might conceivably
mutate or exchange genetic material with indigenous
natural microorganisms in a way that makes the built-in
controls ineffectual.

Given these uncertainties, it would be prudent to
adopt the “precautionary principle” and treat synthetic
microorganisms as dangerous until proven harmless.
According to this approach, all organisms containing
assemblies of BioBricks would have to be studied under a
high level of biocontainment (Biosafety Level 3 or even
4) until their safety could be demonstrated in a
definitive manner. As George Church argued in
Nature in 2005, “Learning from gene therapy, we
should imagine worst-case scenarios and protect against
them. For example, full physical isolation and confined
lab experiments on human and agricultural pathogens
should continue until we have data on a greater number
of potential consequences—ecological and medical—of
engineering such systems.”

The Risk of Testing in
the Open Environment

By definition, some of the
proposed applications of synthetic biology, such as
biosensing, agriculture, and bioremediation (for
example, cleaning up soil contaminated with toxic
chemicals), would involve the use of synthetic
microorganisms in the open environment. To date, only a
small number of GEMs have been developed for
applications outside of the laboratory or containment
facility. According to the U.S. Department of
Agriculture’s Animal and Plant Health Inspection
Service, GEMs may be developed and used for agricultural
purposes, such as enriching soil, without a permit if
the “recipient microorganisms...are not plant pests
and...result from the addition of genetic material
containing only noncoding regulatory regions.”

With respect to bioremediation, the Environmental
Protection Agency requires a stringent risk assessment
before it will approve the release into the environment
of a GEM that can break down specific pollutants.
Although few GEMs have been developed for this purpose,
including genetically modified strains of the common
soil bacterium Pseudomonas putida, they have been
tested only in the laboratory and in one field test
carried out in 1996 under tightly controlled conditions.
In that experiment, Gary Sayler and his colleagues at
the University of Tennessee’s Center for Environmental
Biotechnology used soil lysimeters, steel-lined tanks
measuring eight feet in diameter and filled with a large
volume of soil, to monitor bioengineered bacteria as
they degraded a toxic chemical. Because of the uncertain
ecological impacts of conducting such experiments in the
open environment, however, no GEMs developed for
bioremediation are currently in the regulatory
pipeline.

Theoretically, three types of negative effects could
result from releasing a synthetic microorganism into the
environment. First, the organism could disrupt local
biota or fauna through competition or infection that, in
the worst case, could lead to the extinction of one or
more wild species. Second, once a synthetic organism has
successfully colonized a locale, it might become endemic
and thus impossible to eliminate. Third, the synthetic
organism might damage or disrupt some aspect of the
habitat into which it was introduced, upsetting the
natural balance and leading to the degradation or
destruction of the local environment.

U.S. government agencies, foreign governments, and
intergovernmental organizations all take different
approaches to assessing the risks associated with the
deliberate release of a GEM into the open environment.
Generally speaking, though, an inventor seeking
permission to release a GEM must answer five questions
in detail:

Are you thoroughly familiar with the microorganism
donating the genetic material?

Are you thoroughly familiar with the microorganism
receiving the genetic material?

Are you thoroughly familiar with the environment
of the site into which the genetically engineered
microorganism will be introduced?

Will you be able to contain the introduced
organism to the designated site of
introduction?

Should containment fail, do you know the damage
that the escaped microorganism would cause to human
health and/or the environment?

Based on the answers to these five questions, a
regulatory agency can perform an objective risk
assessment of the proposed release of a GEM. It is by no
means clear, however, that one could answer these
questions for a synthetic microorganism. Because a
microbe constructed from BioBricks would not contain
genetic material transferred from another species,
Questions 1 and 2 are not relevant as stated, although
the “familiarity” criterion is key. Could the inventor
of a synthetic microorganism be said to be truly
“familiar” with it? On the one hand, the inventor would
know every BioBrick making up the genetic circuitry of
the organism. On the other hand, he or she would have
little understanding of the organism’s emergent
properties, including how the synthetic microbe will
interact with other living entities after its release
into the ecosystem. Assuming that the answer to Question
3 (familiarity with the environment) is “yes,” the
answer to Question 4 must inevitably be “no” when
dealing with self-replicating synthetic microorganisms.
Thus, the answer to Question 5 is critical. Because of a
lack of empirical evidence, the inventor of a synthetic
microorganism could not predict the effects of its
release on human health and the environment with any
degree of confidence.

Given these uncertainties, scientists seeking to
develop synthetic microorganisms for applications
outside a containment facility will need to develop new
ways to assess their impact on the environment. One
approach is to perform systematic testing in an
experimental ecosystem that has been designed and
constructed by biologists to analyze ecological
dynamics. There are two types of model ecosystems: a
“microcosm,” which varies in size from a few milliliters
to 15 cubic meters, and a “mesocosm,” which is larger
than 15 cubic meters. These model systems consist of
elements of a natural ecosystem, such as soil,
vegetation, lake water, and sediment, which are brought
together in a container such as an aquarium, an
earth-lined pond, or a PVC tank, and allowed to
equilibrate. (The soil lysimeter described above is a
type of mesocosm.) Ideally, a model ecosystem should be
sufficiently realistic and reproducible to serve as a
bridge between the laboratory and a field test in the
open environment.

Microcosm and mesocosm studies have been useful in
several environmental applications, such as measuring
the stress placed on various types of ecosystems by
synthetic chemicals, natural microorganisms, and GEMs.
In addition, model ecosystems have served to estimate
the extent to which the foreign genetic material
introduced into a GEM can be transferred to other
organisms or can persist by itself in the environment.
However, some scientists and regulatory agencies have
rejected data from microcosm and mesocosm studies
because of a lack of consistency in the way the
experiments were performed and the results interpreted.
With this problem in mind, it may be necessary for the
synthetic biology community to develop a standardized
methodology for testing the environmental impact of its
inventions.

One of the lessons from the history of recombinant
DNA research is that the products made by
genetically engineered microbes are no more hazardous
than those manufactured by more traditional methods.
Thus, for drugs and proteins made by synthetic
microorganisms (such as the artemisinin precursor
produced in yeast), U.S. regulators will probably focus
on the safety of the final product rather than the
method of production. In contrast, countries in Western
Europe and other parts of the world have taken a more
restrictive approach to genetically modified foods and
may likewise be inclined to discriminate against drugs
and other items manufactured by synthetic
microorganisms.

The Risk of Deliberate
Misuse

The 1972 Biological and
Toxin Weapons Convention (BWC) bans the development,
production, stockpiling, and transfer of “microbial or
other biological agents, or toxins whatever their origin
or method of production, of types and in quantities that
have no justification for prophylactic, protective or
other peaceful purposes.” Thus, the BWC implicitly
prohibits the synthesis of known or novel microorganisms
for hostile purposes. Moreover, if synthetic organisms
were designed to produce toxins, then the development
and production of these poisons for weapons purposes
would be prohibited by both the BWC and the 1993
Chemical Weapons Convention. Nevertheless, because the
BWC has not been signed and ratified by every country,
lacks formal verification mechanisms, and does not bind
non-state entities such as terrorist organizations, it
does little to prevent the deliberate misuse of
synthetic biology for hostile purposes.

One potential misuse of synthetic biology would be to
recreate known pathogens (such as the Ebola virus) in
the laboratory as a means of circumventing the legal and
physical controls on access to “select agents” that pose
a bioterrorism risk. Indeed, the feasibility of
assembling an entire, infectious viral genome from a set
of synthetic oligonucleotides has already been
demonstrated for poliovirus and the Spanish influenza
virus. As DNA synthesis technology improves, the
assembly of even larger viruses (such as variola, the
causative agent of smallpox) may eventually become
feasible. J. Craig Venter noted, in testimony before a
Senate subcommittee in 2005, that although a
bioterrorist could use synthetic genomics to make a
pathogenic virus, “the number of pathogens that can be
synthesized today is small and limited to those with
sequenced genomes. And for many of these the DNA is not
infective on its own and poses little actual threat. Our
concern is what the technology might enable decades from
now.”

Indeed, projecting a decade or more into the future,
some analysts have made dire predictions about the
potential misuse of synthetic biology techniques for the
development of more lethal or militarily effective
biological warfare agents. In November 2003, for
example, an expert panel set up by the U.S. Central
Intelligence Agency released a short white paper that
concludes, “Growing understanding of the complex
biochemical pathways that underlie life processes has
the potential to enable a class of new, more virulent
biological agents engineered to attack distinct
biochemical pathways and elicit specific effects.” This
unclassified report provides no details concerning the
expertise, equipment, and facilities that would be
required to develop such engineered biowarfare agents,
nor a time estimate for how long the development process
might take.

In a similar effort at prediction, Mark Wheelis, a
microbiologist at the University of California, Davis,
painted a frightening picture of synthetic biology
twenty years or more into the future. Among his
predictions in a 2004 Arms Control Today article:
“Living synthetic cells will likely be made in the next
decade; synthetic pathogens more effective than wild or
genetically engineered natural pathogens will be
possible sometime thereafter....Such synthetic cellular
pathogens could be designed to be contagious or
noncontagious, lethal or disabling, acute or
persistent.”

How should one assess these predictions about the
potential misuse of synthetic biology for hostile
purposes? At present, the primary threat of misuse
appears to come from state-level biological warfare
programs, some of which probably exploit advanced
molecular biology techniques. It is known that Soviet
weapons scientists conducted genetic engineering
research with dangerous pathogens, such as those that
cause anthrax, plague, and tularemia. Could scientists
possessing this expertise employ synthetic biology to
design and construct an entirely artificial pathogen
that is significantly more deadly and robust than those
that already exist in nature?

In fact, such a scenario is extremely unlikely. To
create such an artificial pathogen, a capable synthetic
biologist would need to assemble complexes of genes
that, working in unison, enable a microbe to infect a
human host and cause illness and death. Designing the
organism to be contagious, or capable of spreading from
person to person, would be even more difficult. A
synthetic pathogen would also have to be equipped with
mechanisms to block the immunological defenses of the
host, characteristics that natural pathogens have
acquired over eons of evolution. Given these daunting
technical obstacles, the threat of a synthetic
“super-pathogen” appears exaggerated, at least for the
foreseeable future.

The most likely misapplication of synthetic biology
for hostile purposes involves the recreation of
known pathogenic viruses in the laboratory.
Contrary to popular belief, however, a biological weapon
is not merely an infectious agent but a complex system
consisting of (1) a supply of pathogen, either produced
in the form of a wet slurry or dried and milled into a
dry powder; (2) a complex “formulation” of chemical
additives that is mixed with the agent to stabilize it
and preserve its infectivity and virulence during
storage; (3) a container to store and transport the
formulated agent; and (4) an efficient dispersal
mechanism to disseminate the formulated agent as a
fine-particle aerosol that can infect the targeted
personnel through the lungs. Finally, the aerosol cloud
must be released under optimal atmospheric and
meteorological conditions if it is to inflict casualties
over a large area. Given the major technical hurdles
associated with weaponization and delivery, the advent
of synthetic biology is unlikely to cause a dramatic
increase in the threat of bioterrorism.

Nevertheless, two possible scenarios for the
deliberate misuse of synthetic biology provide some
grounds for concern. The first involves a “lone
operator,” such as a highly trained molecular biologist
who develops an obsessive grudge against certain
individuals or groups (or society as a whole). If
Theodore Kaczynski, the “Unabomber,” had been a
microbiologist instead of a mathematician, he might have
fit this profile; perhaps the perpetrator of the 2001
anthrax-letter attacks does fit it. So-called “lone
wolf” terrorists have proven very innovative and
difficult to locate; if armed with a weapon of mass
destruction, such a lone operator could cause as much
damage as an organized group.

How likely is this lone operator scenario? In any
large population of professionals, a small minority may
be prepared to use their skills for illicit purposes.
Thus, the growing synthetic biology community can be
expected to include a few individuals with access to
laboratory equipment and supplies who are highly
intelligent and well-trained but also deeply
disgruntled, have sociopathic tendencies, or wish to
prove something to the world. Such an individual might
work alone to synthesize a natural pathogen or one
incorporating foreign virulence factors. Possible
motivations might include inflicting harm on a former or
current employer, lover, or a hated ethnic group,
profiting from blackmail, eliminating rivals, obtaining
perverse pleasure from overcoming technical challenges,
or demonstrating scientific and technical
superiority.

A lone operator with expertise in synthetic biology
would also have a number of characteristics that would
pose special difficulties for those seeking to prevent
or defend against terrorist attacks. He would not be
restricted in his actions by group decision-making and
could purchase dual-use equipment and materials for a
DNA synthesis laboratory, none of which would provide an
obvious tip-off of illicit activity. And precisely
because he would be working solo, a lone operator would
be unlikely to be discovered by the intelligence
community or the police before he strikes.

The pool of people capable of misusing synthetic
biology is currently limited to the small number of
undergraduates, graduate students, and senior scientists
who constitute the research community—probably fewer
than 500 people in early 2006. In the future, however,
the number of capable individuals will grow rapidly as
researchers are drawn to this exciting and dynamic
field.

The second scenario of concern is that of a
“biohacker,” an individual who does not necessarily have
malicious intent but seeks to create bioengineered
organisms out of curiosity or to demonstrate his
technical prowess—a common motivation of many designers
of computer viruses. The reagents and tools used in
synthetic biology will eventually be converted into
commercial kits, making it easier for biohackers to
acquire them. Moreover, as synthetic-biology training
becomes increasingly available to students at the
college and possibly even high-school levels, a “hacker
culture” may emerge, increasing the risk of reckless or
malevolent experimentation.

Mitigating the
Risks

The risks of inadvertent
or deliberate harm from synthetic biology clearly
warrant a policy response. Although some scientists
consider it premature to consider ways of regulating the
field at such an early stage in its development,
prudence suggests that it is better to start addressing
the problem early, rather than having to react after an
unanticipated mishap or disaster has provoked a
political backlash.

Returning to the historical record, more than three
decades of experience have shown that the NIH Guidelines
governing recombinant DNA research have functioned
reasonably well to protect scientists and the public
from potential hazards, while allowing science to
advance relatively unhindered. The main concerns about
the possible hazards from GEMs have shifted over the
years from laboratory research to field testing and use.
Nevertheless, public suspicions persist, particularly in
Western Europe, about the safety of genetically
engineered foods. It is therefore important to consider
how the public will respond to the commercial
applications of synthetic biology. Although the first
such products will not appear for several years, one can
imagine the impact of a news report that a team of
scientists has created an entirely new life form that is
busily replicating itself in a laboratory. Fear of the
unknown, whether rational or irrational, might lead to a
hasty or inappropriate response, one that unnecessarily
impedes scientific progress or ineffectively protects
the public good.

Yet it also seems likely that, given the difficulty
of anticipating and assessing the risks associated with
synthetic organisms, synthetic biology will require a
new approach to regulation that differs significantly
from the NIH Guidelines on recombinant DNA. Accordingly,
it would be useful to bring several leading
practitioners of synthetic biology together with
biosafety experts, social scientists, ethicists, and
legal scholars to brainstorm about reasonable approaches
for the oversight and control of such research. The
following elements of a regulatory regime might be
considered:

Screening of oligonucleotide orders. At
present, it is possible to place orders for
oligonucleotides and genes over the Internet to custom
supply houses, which synthesize any DNA sequence upon
request and keep the transaction confidential. As
University of Washington biotechnology analyst Rob
Carlson has noted, oligonucleotide producers have
emerged in several countries around the world, including
nations such as China and Iran. A U.S. gene-synthesis
company, Blue Heron Biotechnology, voluntarily uses
special software to screen all oligonucleotide and gene
orders for the presence of DNA sequences from “select
agents” of bioterrorism concern. When such a sequence is
detected, the request is denied, although there is
currently no procedure for reporting such incidents to
U.S. government authorities. Nevertheless, suppliers are
currently under no legal obligation to screen their
orders, and because many clients value confidentiality,
companies might put themselves at a competitive
disadvantage by doing so. There are two possible
solutions to this problem. First, Congress could pass a
law requiring U.S. suppliers to screen all
oligonucleotide and gene orders for pathogenic DNA
sequences. Alternatively, suppliers could agree among
themselves to screen orders voluntarily, or legitimate
researchers could choose to patronize only those
companies that do so. Because the trade involves several
countries, however, an effective regulatory regime would
have to be international in scope.

Ecological modeling of synthetic
microorganisms. Given the difficulty of predicting
the risks to public health and the environment posed by
synthetic microorganisms, it will be essential to study
the ecological behavior of such agents in enclosed
microcosms or mesocosms that model as accurately as
possible the ecosystem into which the organism will be
released. Such studies should examine the extent to
which the genetic material from a synthetic
microorganism is transferred to other organisms or
persists intact in the environment. In the event that
the uncertainties associated with the liberation of
synthetic microbes prove to be irreducible, it may be
necessary to ban all uses in the open environment until
a robust risk assessment can be conducted for each
proposed application.

Oversight of research. Research in synthetic
biology may generate “dual-use” findings that could
enable proliferators or terrorists to develop biological
warfare agents that are more lethal, easier to
manufacture, or of greater military utility than today’s
bioweapons. In rare cases, it may be necessary to halt a
proposed research project at the funding stage or, if
unexpectedly sensitive results emerge that could
threaten public health or national security, to place
constraints on publication. Relevant guidelines for the
oversight of “dual-use” research are currently being
developed by the U.S. government’s National Scientific
Advisory Board for Biosecurity and should eventually be
“harmonized” internationally.

Public outreach and education. Because of the
potential for intense controversy surrounding synthetic
biology, public outreach and education are needed even
at this early stage in the field’s development. Although
it is often difficult to persuade scientists to leave
the laboratory for even a few hours to participate in a
public discussion of their work and its implications for
society, such efforts should be encouraged because they
generate good will and may help to prevent a future
political backlash that could cripple the emerging field
of synthetic biology.

Synthetic Biology and
the Public Good

At present, synthetic
biology’s myriad implications can be glimpsed only
dimly. The field clearly has the potential to bring
about epochal changes in medicine, agriculture,
industry, ethics, and politics, and a few decades from
now it may have a profound influence on the definition
of life, including what it means to be human. Some
critics consider the idea of creating artificial
organisms in the laboratory to be a frightening example
of scientific hubris, evocative of Faust or Dr.
Frankenstein. Yet given the momentum and international
character of research in synthetic biology, it is
already too late to impose a moratorium, if indeed one
was ever contemplated.

Instead, practitioners and policy analysts should
begin a wide-ranging debate about how best to guide
synthetic biology in a safe and socially useful
direction without smothering it in the cradle. In so
doing, it will be useful to hark back to the enlightened
group of biologists who met at Asilomar in 1975 to
discuss another exciting new technology—recombinant
DNA—that appeared to offer great benefits and unknown
dangers. Their deliberations led to the decision to
proceed with caution, subjecting potentially dangerous
experiments to careful risk assessment and oversight.
That approach, which has since proven remarkably
successful, bears emulating today. In the process,
however, we may discover that synthetic biology poses
novel regulatory and ethical challenges as scientists
learn how to manipulate the most basic elements of
living systems.

For the general
reader:

Philip Ball, “Starting
from scratch,” Nature, vol. 431, no.
7009 (October 7, 2004), pp.
624-626.
George Church, “Let
us go forth and safely multiply,”
Nature, vol. 438, no. 7067 (November 24,
2005), p. 423.
Dan Ferber, “Microbes
made to order,” Science, vol. 303, no.
5655 (January 9, 2004), pp.
158-161.
Alan Moses, “Intelligent
design: Playing with the building blocks of
biology,” Berkeley Science Review, vol.
5, no. 1 (Spring 2005), pp.
34-40.
W. Wayt Gibbs, “Synthetic
life,” Scientific American, May 2004,
pp. 74-81.
Oliver Morton, “Life,
Reinvented,” Wired, vol. 13, no. 1
(January 2005), pp. 168-175.

Technical
articles:

Steven A. Benner and A.
Michael Sismour, “Synthetic
biology,” Nature Reviews Genetics, vol.
6, no. 7 (July 2005), pp.
533-543.
Robert Brent, “A
partnership between biology and engineering,”
Nature Biotechnology, vol. 22, no. 10
(October 2004), pp.
1211-1214.
Drew Endy, “Foundations
for engineering biology,” Nature, vol.
438, no. 7067 (November 24, 2005), pp.
449-453.
Jeff Hasty, David
McMillen, and J. J. Collins, “Engineered
gene circuits,” Nature, vol. 420, no.
6912 (November 14, 2002), pp.
224-230.
Ryan McDaniel and Ron
Weiss, “Advances
in synthetic biology: on the path from prototypes
to applications,” Current Opinion in
Biotechnology, vol. 16, no. 4 (August 2005),
pp. 476-483.

Major
Scientific Papers:

Mariette R.
Atkinson, Michael A. Savageau, Jesse T. Myers, and
Alexander J. Ninfa, “Development
of genetic circuitry exhibiting toggle switch or
oscillatory behavior in Escherichia
coli,” Cell, vol. 113, no. 5 (May
30, 2003), pp. 597-607.
Subhayu Basu,
Rishabh Mehreja, Stephan Thiberge, Ming-Tang Chen,
and Ron Weiss, “Spatiotemporal
control of gene expression with pulse-generating
networks,” Proceedings of the National
Academy of Sciences, vol. 101, no. 17 (April
27, 2004), pp. 6355-6360.
Jeronimo Cello,
Aniko V, Paul, and Eckard Wimmer, “Chemical
synthesis of poliovirus cDNA: Generation of
infectious virus in the absence of natural
template,” Science, vol. 297, no. 5583
(August 9, 2002), pp. 1016-1018.
Leon Y. Chan, Sriram
Kosuri, and Drew Endy, “Refactoring
bacteriophage T7,” Molecular Systems
Biology, doi:10.1038/msb4100025 (published
online: September 13, 2005).
Michael B. Elowitz
and Stanislaw Leibler, “A
synthetic oscillatory network of transcriptional
regulators,” Nature, vol. 403, no. 6767
(January 20, 2000), pp. 335-338.
Timothy S. Gardner,
Charles R. Cantor, and James J. Collins, “Construction
of a genetic toggle switch in Escherichia
coli,” Nature, vol. 403, no. 6767
(January 20, 2000), pp. 339-342.
Calin C. Guet,
Michael B. Elowitz, Weihong Hsing, and Stanislas
Leibler, “Combinatorial
synthesis of genetic networks,”
Science, vol. 296, no. 5572 (May 24, 2002),
pp. 1466-1470.
John I. Glass,
Nacyra Assad-Garcia, Nina Alperovich, Shibu
Yooseph, Matthew R. Lewis, Mahir Maruf, Clyde A.
Hutchinson III, Hamilton O. Smith, and J. Craig
Venter, “Essential
genes of a minimal bacterium,” Proceedings
of the National Academy of Sciences, vol. 103,
no. 2 (January 10, 2006), pp.
425-430.
Beat P. Kramer,
Alessandro Usseglio Viretta, Marie Daoud-El Baba,
Dominique Aubel, Wilfried Weber, and Martin
Fussenegger, “An
engineered epigenetic transgene switch in
mammalian cells,” Nature Biotechnology,
vol. 22, no. 7 (July 2004), pp.
867-870.
Anselm Levskaya,
Aaron A. Chevalier, Jeffrey J. Tabor, Zachary
Booth Simpson, Laura A. Lavery, Matthew Levy, Eric
A. Davidson, Alexander Scouras, Andrew D.
Ellington, Edward M. Marcotte, and Christopher A.
Voigt, “Engineering
Escherichia coli to see light,”
Nature, vol. 438, no. 7067 (November 24,
2005), pp. 441-442.
Oliver Rackham and
Jason W. Chin, “A
network of orthogonal ribosome•mRNA pairs,”
Nature Chemical Biology, vol. 1, no. 3
(August 2005), pp. 159-166.
Dae-Kyun Ro, Eric M.
Paradise, Mario Ouellet, Karl J. Fisher, Karyn L.
Newman, Jay D. Keasling, et al., “Production
of the antimalarial drug precursor artemisinic
acid in engineered yeast,” Nature, vol.
440, no. 7086 (April 13, 2006), pp.
940-943.
Hamilton O. Smith,
Clyde A. Hutchinson III, Cynthia Pfannkoch, and J.
Craig Venter, “Generating
a synthetic genome by whole genome assembly: φX174
bacteriophage from synthetic
oligonucleotides,” Proceedings of the
National Academy of Sciences, vol. 100, no. 26
(December 23, 2003), pp.
15440-15445.
David Sprinzak and
Michael B. Elowitz, “Reconstruction
of genetic circuits,” Nature, vol. 438,
no. 7067 (November 24, 2005), pp.
443-448.
Jingdong Tian, Hui
Gong, Nijing Sheng, Xiaochuan Zhou, Erdogan
Gulari, Xiolian Gao, and George Church, “Accurate
multiplex gene synthesis from programmable DNA
microchips,” Nature, vol. 432, no. 7020
(December 23, 2004), pp.
1050-1054.
Terence M. Tumpey,
Christopher F. Basler, Patricia V. Aguilar, Hui
Zeng, et al., “Characterization
of the reconstructed 1918 Spanish influenza
pandemic virus,” Science, vol. 310, no.
5745 (October 7, 2005), pp. 77-80.
Lei Wang, Ansgar
Brock, Brad Herberich, and Peter G. Schultz, “Expanding
the genetic code of Escherichia coli,”
Science, vol. 292, no. 5516 (April 20,
2001), pp. 498-500.
Yohei Yokobayashi,
Ron Weiss, and Frances H. Arnold, “Directed
evolution of a genetic circuit,”
Proceedings of the National Academy of
Sciences, vol. 99, no. 26 (December 24, 2002),
pp.
16587-16591.

Jonathan B. Tucker is a senior fellow at
the Center for Nonproliferation Studies (CNS) of the
Monterey Institute of International Studies, where he
specializes in biological and chemical weapons issues.
He is the author, most recently, of War of Nerves: Chemical Warfare from World
War I to Al-Qaeda (Pantheon, 2006).
Raymond A. Zilinskas, formerly a clinical
microbiologist, is the director of the Chemical and
Biological Weapons Nonproliferation Program at CNS. He
is the editor of Biological Warfare: Modern Offense and
Defense (Lynne Rienner, 1999) and
co-editor of the Encyclopedia of Bioterrorism
Defense (Wiley, 2005). Support for this
paper was provided by a grant from the Carnegie
Corporation of New York. The authors are also grateful
to the following individuals for assistance and comments
on earlier drafts: Adam P. Arkin, Erika Burleson, Philip
Campbell, and Steven M. Maurer.

Jonathan B. Tucker and
Raymond A. Zilinskas, "The Promise and Perils of
Synthetic Biology," The New Atlantis, Number 12,
Spring 2006, pp.
25-45.

Published by the Ethics and
Public Policy Center, Washington,
D.C.