May 24, 2010 — Scientists at the Venter Institute have reported the creation of the first "synthetic cell" — Mycoplasma capricolum cells that received and are controlled by a laboratory-assembled genome of Mycoplasma mycoides. Although some scientists note that only the genome is synthetic, the developers explain that the recipient cell's cytoplasm is diluted with each division. Thus, after 30 generations in culture, some progeny not only have a chromosome of synthetic origin but also contain no proteins from the original cell.
The achievement "grew out of our efforts over the past 15 years to build a minimal cell that contains only essential genes," said authors of the study, posted by Science May 20 on its Science Express Web site. These efforts included sequencing the Mycoplasma genitalium genome in 1995, transplanting the genome from 1 bacterial strain into cells of another strain, and in 2008, assembling a full bacterial genome from chemically synthesized DNA fragments.
The present study by senior author J. Craig Venter, PhD, founder, chairman, and president of the J. Craig Venter Institutes, Rockville, Maryland, and San Diego, California, and his colleagues combined their ability to transplant a bacterial genome with the technological expertise to build that genome from DNA fragments. Because M genitalium grows slowly, the investigators chose the more rapidly growing M mycoides subspecies capri as the donor strain and M capricolum subspecies capricolum as the recipient.
The synthetic donor genome was carefully constructed using sequencing information from 2 laboratory strains of M mycoides. Genomes of the 2 strains diverged at 95 sites, so differences with biological significance were corrected to match those of the genome that had been cloned successfully in yeast cells. The 19 remaining sites appeared to have no biological significance but serve to differentiate between the synthetic and natural genomes.
The complex assembly process started with DNA sequences just over 1000 base pairs (1080 bp) long, which were combined to produce 10,080-bp (10-kb) intermediates. After sequences were verified, these units were assembled to form 100-kb intermediates, and finally the 1,077,947-bp synthetic genome of M mycoides. Assembly occurred in yeast, and the synthetic genome was cloned in yeast cells and finally transplanted into M capricolum recipient cells. Markers built into the synthetic chromosome and expressed in culture enabled researchers to identify cells that had incorporated the synthetic M mycoides genome.
"99 out of 100 of Our Experiments Haven't Worked"
The research group was already very familiar with M mycoides — a bacterium they had worked with in transplant experiments for several years. "If you can imagine, 99 out of 100 of our experiments haven't worked, and this has been almost a decade of complex problem solving to get to this point," said Dr. Venter in an interview on NPR's Science Friday. "So we wanted to start the experiments with something that we at least knew would be compatible with life."
Nevertheless, their work encountered obstacles. One challenge was a single-bp deletion that disrupted a gene essential for chromosomal replication and prevented successful transplantation of the synthetic chromosome. "We were previously unaware of this mutation," said the authors, noting that their "success was thwarted for many weeks" by the deletion. The glitch involved only 1 missing nucleotide pair out of more than a million but caused a lengthy delay to repair the affected section of the genome.
After the error was corrected, the synthetic genome was successfully transplanted into recipient cells, producing bacteria with expected phenotypes that continue to self-replicate. "The demonstration that our synthetic genome gives rise to transplants with the characteristics of M. mycoides cells implies that the DNA sequence upon which it is based is accurate enough to specify a living cell with the appropriate properties," observe the authors.
Apart from scoring a coup as the first "proof of principle for producing cells based upon genome sequences designed in the computer," the work has attracted widespread attention from the media, the federal government, and bioethicists.
In a response from the White House, President Obama designated "synthetic biology" as the first study project for his Commission for the Study of Bioethical Issues. His May 20 letter to the chair of the commission instructed them to consider the environmental, medical, and security benefits of this research, as well as its potential risks. Their report and recommendations are due within 6 months.
Dr. Venter anticipated the potential ethical implications of the research more than a decade ago. "The first bioethical review was published in 1999, before we did the first experiments, and that's a review that we had asked for," said Dr. Venter on National Public Radio. "We were concerned that despite all the discussion — there's over 100,000 blogs on the Internet before this publication — that still this would be the first time the majority of people heard about this research, and we figured there would be some of the usual shock and responses to it."
"Scientists Do Not Know Enough About Biology to Create Life"
Eight synthetic-biology experts aired their views on "Life After the Synthetic Cell" in a May 20 opinion piece in Nature. One of these experts, Arthur Caplan, PhD, director of the Center for Bioethics, University of Pennsylvania, Philadelphia, saw the study as a demonstration that "the material world can be manipulated to produce what we recognize as life. In doing so they bring to an end a debate about the nature of life that has lasted thousands of years," he writes.
To his mind, the metaphysical views of the major religions are "cast into doubt by the demonstration that life can be created from non-living parts, albeit those harvested from a cell. Venter's achievement would seem to extinguish the argument that life requires a special force or power to exist."
Martin Fussenegger, PhD, professor of biotechnology and bioengineering and director of the Institute for Chemical and Bioengineering, ETH Zurich, Basel, Switzerland, reflected a different perspective in Nature: "It is this speed [with which new organisms can be generated], and the appearance of a new technology associated with living systems, that trigger discomfort," he noted.
If a species with a programmed synthetic genome were to become useful, Dr. Fussenegger expects that it would be restricted to the production environment. "If it were ever to face a natural ecosystem, it would be challenged by rivals and would be unprepared for the competition." Despite their origin, synthetically generated organisms would still be subject to competition and to evolution, says Dr. Fussenegger, "a natural law that cannot be tricked."
And with casual skepticism, Jim Collins, PhD, professor, Department of Biomedical Engineering, and codirector of the Center for BioDynamics, College of Engineering, Boston University, Massachusetts, responded to the hype: "The work...is an important advance in our ability to re-engineer organisms; it does not represent the making of new life from scratch," he pointed out.
Dr. Collins considers the "synthetic cell" as synthetic only "in the sense that its DNA is synthesized, not in that a new life form has been created. Its genome is a stitched-together copy of the DNA of an organism that exists in nature, with a few small tweaks thrown in.... Frankly," said Dr. Collins, "scientists do not know enough about biology to create life."
Science Express. Published online May 20, 2010.
Nature. Published online May 20, 2010.
Science Friday. Aired May 21, 2010.
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Cite this: Did Scientists Create a Synthetic Cell? It Depends Who You Ask - Medscape - May 24, 2010.