Genome Engineering

J Craig Venter and colleagues at the J Craig Venter Institute have created the first self-replicating, synthetic bacterial cell, based on a synthetic genome transplanted into a host bacterial cell, and published the research in Science in May 2010.

To create the cell, researchers designed and assembled a synthetic genome for Mycoplasma mycoides from synthesised fragments around 1080 base pairs long, with overlapping ends. The synthetic DNA sequence was made up of essential genes and designed gene deletions and polymorphisms, with ‘watermark’ sequences to identify the engineered cells, along with some mutations acquired during the building process.

The researchers transplanted the completed genome into Mycoplasma capricolum, successfully creating a fully replicating synthetic cell controlled by the M mycoides genome, which demonstrated the M mycoides phenotype, rather than that of the M capricolum recipient cell. Though the cytoplasm in the created cell is not truly synthetic, as it comes from the M capricolum recipient cell, once replication has created a colony, there will no longer be any proteins from the original cell still present.

Problems

Seemingly simple and minor errors can cause major issues in research of this type. The researchers were delayed by a number of weeks by a single base pair deletion creating a frameshift in the gene dnaA, which is essential for chromosome replication. “One wrong base out of over one million in an essential gene rendered the genome inactive, while major genome insertions and deletions in non-essential parts of the genome had no observable impact on viability,” state Venter et al.

Signatures and watermarks

The synthetic genome includes a signature or ‘watermark, based on a code created from the four bases, C, A, G and T, which have been used to represent letters, numbers and punctuation marks. The watermark includes the serial number of the bacterium, JCVI-syn1.0, along with the names of the 46 contributors, three quotes, and a web address to use if the code is cracked. The quotes include James Joyce – “To live, to err, to fall, to triumph, to recreate life out of life.”

As well as providing a quirky puzzle for scientists, this watermarking will identify the bacterium as that one created in the laboratory, allowing it to be tracked if it escapes, and also potentially deterring counterfeiters and patent infringers, as Venter hopes to gain patent protection on his creation, through his company Synthetic Genomics.

Steps on the way

The creation of this cell has been 15 years in the making, beginning with the sequencing of Mycoplasma genitalium in 1995. In 2003, J Craig Venter received a $3 million grant to develop an artificial genome. The next step in 2007 was the transplantation of a bacterial genome from M mycoides to M capricolum, creating a viable M capricolum bacterium, followed by a similar exercise in 2009, transplanting a genome that had been cloned and genetically modified in yeast.

In the future…

Like all major advances in genetic engineering, there are risks associated with this science, and it will need to be monitored carefully from an ethical and safety standpoint. While some pundits have argued that this is not a truly synthetic cell, as it is just a synthetic genome placed inside an existing bacterial cell, this research may open the door to the creation of truly synthetic life. It demonstrates the incredible potential of genetic engineering, and has the potential to create cells that can be engineered to produce all manner of products, from drugs and industrial chemicals to food and carbon-neutral biofuels.

Further information: Listen to an interview with J Craig Venter.