Scientists take major step towards 'synthetic life': first bacterial genome transplantation changing one species to another

A major breakthrouh in the life sciences was published in the journal Science today. Researchers at the J. Craig Venter Institute (JCVI) present the results of their work on genome transplantation methods allowing them to transform one type of bacteria into another type dictated by the transplanted chromosome. The work, published by JCVI’s Carole Lartigue, Ph.D. and colleagues, outlines the methods and techniques used to change one bacterial species, Mycoplasma capricolum into another, Mycoplasma mycoides Large Colony (LC), by replacing one organism’s genome with the other one’s genome.

The achievement opens the era of synthetic biology, a revolutionary science field the consequences and applications of which we can only begin to imagine. In order to prepare the public for this news, world leading scientists issued a declaration a few days ago, in which they call for a global push to advance synthetic biology. Prior to this 'Ilulissat Statement', Dr Craig Venter, president of JVCI and founder of the Synthetic Genomics Company, patented the technique for the creation of a 'minimal bacterial genome'.

To alleviate public fears, scientists have repeatedly stressed that synthetic biology may address some of the most daunting problems of our times, such as climate change, energy, health, and water resources. Synthetic biology possibly offers solutions to these issues: microorganisms that convert ubiquitous plant matter to biofuels in a highly efficient manner or that synthesize new drugs or target and destroy rogue cells in the body. Now that a major breakthrough has been achieved, they repeat the message once again:

The successful completion of this research is important because it is one of the key proof of principles in synthetic genomics that will allow us to realize the ultimate goal of creating a synthetic organism. We are committed to this research as we believe that synthetic genomics holds great promise in helping to solve issues like climate change and in developing new sources of energy. - Dr J. Craig Venter, president and chairman, JCVI

Methods and techniques
The JCVI team devised several key steps to enable the genome transplantation. First, an antibiotic selectable marker gene was added to the M. mycoides LC chromosome to allow for selection of living cells containing the transplanted chromosome. Then the team purified the DNA or chromosome from M. mycoides LC so that it was free from proteins (called naked DNA). This M. mycoides LC chromosome was then transplanted into the M. capricolum cells. After several rounds of cell division, the recipient M. capricolum chromosome disappeared having been replaced by the donor M. mycoides LC chromosome, and the M. capricolum cells took on all the phenotypic characteristics of M. mycoides LC cells.

As a test of the success of the genome transplantation, the team used two methods — 2D gel electrophoresis and protein sequencing, to prove that all the expressed proteins were now the ones coded for by the M. mycoides LC chromosome. Two sets of antibodies that bound specifically to cell surface proteins from each cell were reacted with transplant cells, to demonstrate that the membrane proteins switch to those dictated by the transplanted chromosome not the recipient cell chromosome. The new, transformed organisms show up as bright blue colonies in images of blots probed with M. mycoides LC specific antibody.

The group chose to work with these species of mycoplasmas for several reasons — the small genomes of these organisms which make them easier to work with, their lack of cell walls, and the team’s experience and expertise with mycoplasmas. The mycoplasmas used in the transplantation experiment are also relatively fast growing, allowing the team to ascertain success of the transplantation sooner than with other species of mycoplasmas:
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Dr. Lartigue and her team is excited by the results of the research, and the scientists are continuing to perfect and refine the techniques and methods as they move to the next phases and prepare to develop a fully synthetic chromosome.

Genome transplantation is an essential enabling step in the field of synthetic genomics as it is a key mechanism by which chemically synthesized chromosomes can be activated into viable living cells. The ability to transfer the naked DNA isolated from one species into a second microbial species paves the way for next experiments to transplant a fully synthetic bacterial chromosome into a living organism and if successful, “boot up” the new entity.

According to the JCVI there are many important applications of synthetic genomics research including development of new energy sources and as means to produce pharmaceuticals, chemicals or textiles. The research was funded by Synthetic Genomics Inc., Dr Venter's company.

Background and Ethical Considerations
The work described by Lartigue et al. has its genesis in research begun by Dr. Venter and colleagues in the mid-1990’s after sequencing Mycoplasma genitalium and beginning work on the 'minimal genome project'. This area of research, trying to understand the minimal genetic components necessary to sustain life, underwent significant ethical review by a panel of experts at the University of Pennsylvania. The bioethical group's independent deliberations, published at the same time as the scientific minimal genome research, resulted in a unanimous decision that there were no strong ethical reasons why the work should not continue as long as the scientists involved continued to engage public discussion.

In 2003 Drs. Venter, Smith and Hutchison made the first significant strides in the development of a synthetic genome by their work in assembling the 5,386 base pair bacteriophage φX174 (phi X). They did so using short, single strands of synthetically produced, commercially available DNA (known as oligonucleotides) and using an adaptation of polymerase chain reaction (PCR), known as polymerase cycle assembly (PCA), to build the phi X genome. The team produced the synthetic phi X in just 14 days.

Dr. Venter and the team at JCVI continue to be concerned with the societal implications of their work and the field of synthetic genomics generally. As such, the Institute’s policy team, along with the Center for Strategic & International Studies (CSIS), and the Massachusetts Institute of Technology (MIT), were funded by a grant from the Alfred P. Sloan Foundation for a 15-month study to explore the risks and benefits of this emerging technology, as well as possible safeguards to prevent abuse, including bioterrorism. After several workshops and public sessions the group is set to publish a report in summer 2007 outlining options for the field and its researchers.

Images: Colonies of the transformed Mycoplasma mycoides bacterium. Credit: J. Craig Venter Institute

References:
Carole Lartigue, John I. Glass, Nina Alperovich, Rembert Pieper, Prashanth P. Parmar, Clyde A. Hutchison III, Hamilton O. Smith, J. Craig Venter, "Genome Transplantation in Bacteria: Changing One Species to Another", Science, Published Online June 28, 2007, DOI: 10.1126/science.1144622

J. Craig Venter Institute: JCVI Scientists Publish First Bacterial Genome Transplantation Changing One Species to Another - June 28, 2007.