Nature (pg. 624)
October 7, 2004


Genetic engineering is old hat. Biologists are now synthesizing
genomes, altering the genetic code and contemplating new life forms.
Is it time to think about the risks? Philip Ball asks the experts.

Philip Ball[1]

Redesigning Life. That was what Steven Benner wanted to call his 1988
conference in Interlaken, Switzerland. A chemist now at the University
of Florida in Gainesville, Benner was organizing the meeting to
explore the possibilities for making artificial chemical systems that
mimic essential features of living things.

But his title caused such a furore among prospective attendees that
Benner had to tone it down to Redesigning the Molecules of Life.
"Individuals as distinguished as Nobel laureates were convinced that
the title would incite anti-recombinant-DNA riots in Switzerland,"
Benner explains.

Benner's conference helped to define one strand of the emerging
discipline known as synthetic biology, a field that is now raising
worries that won't be deflected simply by semantics. The expanding
toolbox of ways to re-engineer microbes -- and even construct new ones
-- has opened up extraordinary possibilities for biomedical discovery
and environmental engineering. But it also carries potential dangers
that could eclipse the concerns already raised about genetic
engineering and nanotechnology. If biologists are indeed on the
threshold of synthesizing new life forms, the scope for abuse or
inadvertent disaster could be huge.

In a dramatic demonstration of the potential risks, virologist Eckard
Wimmer at the State University of New York at Stony Brook announced in
2002 that his team had built live poliovirus from scratch using mail-
order segments of DNA and a viral genome map that is freely available
on the Internet[1]. The feat put a spotlight on the possibility that
bioterrorists could create even more dangerous organisms -- including
Ebola, smallpox and anthrax -- perhaps endowing them with resistance
to antibiotics.

Creative thoughts

Since then, biologists' abilities to engineer life have bounded ahead.
Wimmer took three years to build his poliovirus, but last November
genome sequencer Craig Venter and his colleagues at the Institute for
Biological Energy Alternatives in Rockville, Maryland, announced that
they had taken just three weeks to assemble a virus that infects
bacteria[2]. At the same time, bacterial cells are being rewired to
perform functions they can't fulfil in nature. And researchers are
getting close to determining the smallest set of genes necessary to
support a living cell, which might make it possible to cook up new
life forms.

Almost 30 years ago, concerns that recombinant DNA technology could
pose risks to human health and the environment prompted leading
molecular biologists to call an unprecedented summit. They gathered at
the Asilomar Conference Center in Pacific Grove, California, in
February 1975, where they decided to voluntarily forego some kinds of
research and to instigate safety measures to prevent abuses of the new

Is it now time for another Asilomar? Researchers involved in synthetic
biology generally agree that more discussion of how to avoid risks is
urgently needed, but have yet to take the formal step of calling for a
summit. Some concerns were aired at a special session at the First
International Meeting on Synthetic Biology, held in June at the
Massachusetts Institute of Technology (MIT) in Cambridge, but it did
not set out to produce policy recommendations.

The reason we face the question of risk at all is that the potential
rewards of pursuing synthetic biology are so great. Protein engineer
Wendell Lim of the University of California, San Francisco, says that
if synthetic biology is successful, it may become possible to treat a
variety of diseases by repairing defective cell functions, targeting
tumours or stimulating growth and regeneration of specific cell types.
Other researchers are hoping to engineer bacteria to make complicated
drugs or to use sunlight to generate clean-burning hydrogen for cars
and power plants.

Synthetic biology is the logical corollary of the realization that
cells, like mechanical or electronic devices, are exquisitely
'designed' -- albeit by evolution rather than on the drawing board.
Their functions are enacted by circuits of interacting genes. As
scientists began to map these circuits in the 1990s, they inevitably
began to wonder whether they could rewire them.

Glowing report

In 2000, biological physicists Michael Elowitz and Stanislas Leibler,
both then working at Princeton University in New Jersey, designed from
scratch a genetic circuit that caused oscillating production of a
fluorescent protein. Bacteria programmed with the circuit glowed
periodically[3]. Other researchers built on this, creating circuits
that could be switched on and off by external signals, or that could
control bacterial population density[4,5].

Now a growing number of researchers are working on ways to alter the
circuitry of cells. Lim, for instance, is retooling some of the
proteins that carry signals within and between cells so that they
respond to different inputs from the environment[6,7]. And chemical
engineer Jay Keasling at the Lawrence Berkeley National Laboratory,
has refitted the gut bacterium Escherichia coli with the circuitry it
needs to synthesize a precursor to the powerful antimalarial drug
artemisinin, a product of the wormwood plant that is currently too
expensive for widespread use. This meant importing ten genes from
other organisms, including wormwood and brewer's yeast, and then
carefully tuning their expression levels[8]. If this proves to be a
cheap, reliable source of the drug, it could transform the treatment
of malaria.

In a parallel development, other researchers have been tinkering with
the building blocks of genes and proteins themselves. Naturally
occurring proteins are built from a standard set of 20 amino acids.
Although these are enough to produce protein chains with a staggering
array of functions, expanding this repertoire might enable the design
of biomolecules with new functions, such as protein-based drugs that
resist being broken down in cells.

In 1989, Peter Schultz, a chemist now at the Scripps Research
Institute in La Jolla, California, reported that he had found a way to
persuade bacteria to incorporate an unnatural amino acid into a
specific protein[9]. This produced enzymes with subtly different
activities. Since then, Schultz has added more than 80 unconventional
amino acids to proteins.

Culture shock

In the same year, Benner persuaded cells to insert a base pair not
used in nature into their DNA[10]. A better understanding of the
different types of molecules that can function as DNA bases will open
a window to the possible chemical ancestors of DNA that might have
existed on primordial Earth, and to the possible genetic systems that
could support life on other worlds. "I suspect that, in five years or
so, the artificial genetic systems that we have developed will be
supporting an artificial life form that can reproduce, evolve, learn
and respond to environmental change," Benner predicts. "This will help
define how life not of earthly origin might appear."

As biologists learn to shape cellular circuits and their molecular
components, developments in the automated chemical synthesis of DNA
are allowing entire genomes to be designed and assembled. Venter's
lightning-fast synthesis of a virus in November was a testament to the
expanding capacity of DNA synthesis machines. By some estimates, next
year's machines will be able to generate sequences about a million
base pairs long -- roughly the size of the genome of Chlamydia, which
causes a common sexually transmitted disease, and a quarter the size
of E. coli's genome.

"Bacterial genomes are within the range of current DNA-synthesis
technology," says John Mulligan, president of the DNA-synthesizing
company Blue Heron Technology in Bothell, Washington. But bacterial
genomes must be embedded within a cell and its attendant biochemical
machinery, making them much harder to synthesize than viruses.
Nevertheless, attempts are under way. In November 2002, Venter made a
high-profile announcement of his intention to build a simple bacterium
starting with machine-made DNA.

Plain and simple

But building a new bacterial genome is not just a matter of chemistry
-- you have to design the circuitry too. That's the hard part, so it's
good to simplify. "An alternative to understanding complexity is to
get rid of it," says Tom Knight, a computer scientist at MIT who
brings an engineer's perspective to synthetic biology.

To this end, Knight is studying one of the simplest organisms known,
Mesoplasma florum, a bacterium that has only 682 genes. The draft
genome of this organism was completed last year, and its metabolic
pathway has been mapped. The 793-kilobase genome seems to contain very
little non-essential DNA, but Knight thinks it can be simplified
further. He is now mapping its circuitry and modelling it on a
computer to see what else can be removed.

All of these technologies combined are raising issues similar to those
that sparked the Asilomar summit. Back then, molecular biologists
realized they had all the tools to genetically modify bacteria -- and
possibly higher organisms -- in just about any way imaginable. The
hope was that bacteria could be engineered to produce drugs such as
human insulin cheaply, and indeed they soon were. The worry was that
no one knew how modified bacteria might fare in the environment --
whether, for example, they might be toxic, or resistant to

Synthetic biology is now raising the bar. Should limits be set on what
is attempted? If so, what should they be and how should they be
enforced? And what steps can be taken to ensure that a rogue
organization, or even a state-sponsored bioweapons programme, does not
use the technology to synthesize a dangerous microbe?

Roger Brent, president of the Molecular Sciences Institute in
Berkeley, California, suggests that one option might be for DNA
synthesis to require a licence. But more importantly, Brent says,
synthetic biology should avoid developing a hacker subculture like
that which spawns computer viruses. Rogue computer hackers hope to
earn respect from their peers by producing particularly clever or
insidious virus programs. Brent urges researchers in the field to
encourage responsible lab culture by not engaging in showy stunts with
no research purpose.

Assembly lines

Even though licensing is currently not required, some DNA synthesis
companies have taken their own steps to avoid inadvertently aiding
irresponsible work. Molly Hoult, senior vice-president of Blue Heron,
says that all the company's orders for DNA are cross-checked against a
database of "biological nasties". If a match turns up, the company
tries to find out more about the customer's research before completing
the order. If it can't easily be checked out, Blue Heron simply turns
the order down. "We walk away from some business," Hoult says.

Such self-policing could become the norm, and scientists might even be
asked to cooperate more closely with intelligence agencies to prevent
the abuse of synthetic biology. An unclassified report by the CIA
released last November warned that synthetic biology could produce
engineered agents "worse than any disease known to man" and suggested
"a qualitatively different working relationship between the
intelligence and biological sciences communities". In particular, the
bioscience community might function as a "living sensor web" that
reports to the government on technical advances that could be used as

But it is not clear whether the risk of bioterrorism will be the most
important concern with synthetic biology. Ron Weiss, an electrical
engineer at Princeton University who spends his time rewiring
bacteria, points out that adding antibiotic-resistance genes to
harmful bacteria is relatively straightforward and has been possible
in principle since the 1970s -- yet it has not become a major focus of
biowarfare. It would be easier and cheaper simply to breed and release
existing harmful organisms than to make new ones. "If I was a
terrorist," says Weiss, "this isn't the way I'd get maximal damage for
my buck."

It is much harder to anticipate the unintentional dangers of synthetic
biology. For example, if new strains of bacteria were developed with
unprecedented capabilities, how could they be kept under control?

One way might be to use built-in safeguards. For instance, the innate
ability of bacteria to respond to high population density, a feature
known as quorum sensing, could be co-opted to activate a self-destruct
mechanism. Another option might be to build gene circuits that
function like the logic gates of computers to count the number of
times a cell divides. After a preset number, the cell would die.

Initial attempts have been made. Unfortunately, Weiss has found that
mutant strains evolve after just a few days that can evade his
population-control mechanism[5]. But he thinks this can be solved by
creating several layers of defence. After all, such redundancy seems
to be built into naturally occurring quorum-sensing bacteria, which do
not mutate to evade their own population controls. "Nature does this
already," Weiss says.

Into the unknown

Yet as synthetic biology develops, it will be hard to anticipate all
the possible problems, whether malevolent or inadvertent. "The
repertoire over the coming decade is limitless," says George Poste, a
bioterrorism expert and director of the Biodesign Institute at Arizona
State University in Tempe. "You'll never identify all the risks."
Poste says that he is not particularly concerned about immediate
dangers, as most researchers are still working with biological
materials isolated from cells, so nothing is likely to escape from the
laboratory. But "fast-forward two decades and it may be quite
different", he adds.

To help quantify risks as they emerge, Poste proposes developing what
he calls a 'calculus of risk' -- an equation that can enumerate a
'risk factor' for new developments and sound an alarm bell when a
certain risk threshold is reached. It's a necessarily crude tool --
Poste's equation includes poorly quantified factors such as the
projected time it would take to convert a new technology for
malevolent use -- but it might at least help to distinguish remote
risks from more immediate ones.

The difficulty of putting a finger on the risks might leave
researchers attending an Asilomar-style conference clutching at
shadows. So for now the talks will remain informal. "This definitely
merits a lot more discussion," says Weiss. "We don't understand the
issues sufficiently yet."

Sooner or later, synthetic biology may find itself facing dangers that
are far more than hypothetical. As Poste puts it: "Biology is poised
to lose its innocence."


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