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Saturday, May 22, 2010

Creation of artificial bacteria

Craig Venter and his team from the J. Craig Venter Institute have built the first bacterial cell with an entirely artificial genome. They placed a synthetic Mycoplasma mycoides genome into a Mycoplasma capricolum cell.

The bacteria M. mycoides was chosen because not only does it have one of the smallest genomes of any living organism, but it doesn’t even need all the genes it does have. Over a fifth of its genes can be disrupted without affecting the bacteria’s growth. Therefore, only about a million base pairs of DNA were required to create a functional synthetic M. mycoides genome.

This was still a daunting procedure, as the best DNA synthesizers cannot construct DNA strands longer than a few thousand base pairs. Thus, the entire genome was created in thousands of sections that then had to be stitched together in the correct order. In addition to the M. mycoides genes, some markers were added to help the scientists identify correctly spliced and functional DNA strands.

Finally, the entire genome was inserted into an M. capricolum cell that had no DNA of its own. These cells served as a host body for the synthetic genome. The newly created hybrid cells grew and reproduced. By any criteria you choose, they were alive.

A few caveats are in order here. First, it’s a far cry from a million base pair bacteria to a couple of billion base pair mammal. Splicing together a million segments of DNA in the correct order is just not within our grasp right now. Second, even if we could synthesize that much DNA and put it together, the error rate is still much too high to expect any viable results. The new bacteria cells, for example, contained eight single base pair changes, an 85 base pair duplication, and an E. coli transposon. In other words, don’t expect to see living synthetic dogs anytime soon.

It's also important to note that the synthetic cells were not really 'new' life forms, since Venter and his associates simply copied an existing genome. Still, this does open the door to creating new types of bacteria by altering the DNA before inserting it.