Friday, June 29, 2007

Genome Transplant turns one species into another

http://www.newscientist.com/article/dn12157-tycoon-succeeds-in-genome-transplant.html

Tycoon succeeds in 'genome transplant'
19:00 28 June 2007
NewScientist.com news service
Peter Aldhous

Call it bacterial alchemy: using a "genome transplant", researchers have turned one species of bacterium into another. The transformation is the latest feat from US genomics pioneer Craig Venter, and marks another step towards his goal of creating a synthetic life-form.

Over the past few years, Venter and his colleagues have defined a minimal genome containing less than 400 genes needed to sustain a free-living cell.

They have done this by systematically knocking out genes in the simple bacterium Mycoplasma genitalium, a sexually-transmitted parasite that infects humans. Venter aims to chemically synthesise this genome from the nucleotide building blocks of DNA, and then put it into a bacterial cell.

Achieving that goal requires a technique to replace a Mycoplasma genome with the synthetic version – and the new work on genome "transplantation" provides proof that this should be possible.

Complex transfer
Venter's team, led by John Glass of the J. Craig Venter Institute in Rockville, Maryland, US, managed to transfer the genome of Mycoplasma mycoides to a related parasite called M. capricolum. Both species infect goats, sheep and cows.

Judging from the proteins they produced, the resulting cells seemed to have completely transformed into M. mycoides.

Mycoplasma cells are too small to manipulate mechanically, so the researchers had to devise laborious chemical and physical methods to extract the genome from one species and introduce it to the other. "It's very simple in concept, very complex in actual execution," Venter says.

The researchers took a strain of M. mycoides that is resistant to the antibiotic tetracycline, broke open the cells and carefully "digested" the proteins, leaving just the intact circular chromosomes, the DNA.

These chromosomes were then incubated with M. capricolum cells in a medium containing a polymer that encourages cell membranes to fuse. The researchers speculate that some M. capricolum cells fused together, encapsulating an M. mycoides chromosome as they did so.

Finally, the researchers treated their cultures with tetracycline, so that only M. capricolum cells containing the M. mycoides genome would survive.

Mysterious process
The transplantation worked in about 1 in every 150,000 cells, but that was enough to give healthy colonies of the transformed bacteria, which did not contain M. capricolum DNA.

Exactly how the M. mycoides genome took over the cell is unclear, but the researchers suggest that cells containing multiple genomes soon divide, with each daughter cell containing just one genome. Those containing the host M. capricolum genome would then have been quickly wiped out by the tetracycline.

Venter, who has ignited controversy by trying to patent his minimal genome, says that the team’s efforts to synthesise it from scratch are still in progress. But once the finished genome is ready, the transplant technique should allow the first "synthetic" bacterium to be created in rapid time. "It could be weeks or months," says Venter.

Journal reference: Science (DOI: 10.1126/science.1144622)

Labels:


Comments: Post a Comment

Subscribe to Post Comments [Atom]





<< Home

This page is powered by Blogger. Isn't yours?

Subscribe to Posts [Atom]