Genome Transplant

Blogged everywhere in cyberspace by now, I’m sure, but just too cool. But of course my immediate thought was the pandora’s box of ethical issues (& potential for scientific-research misconduct) …

Genome Transplantation in Bacteria: Changing One Species to Another
Carole Lartigue, John I. Glass , Nina Alperovich, Rembert Pieper, Prashanth P. Parmar, Clyde A. Hutchison III, Hamilton O. Smith, J. Craig Venter. The J. Craig Venter Institute, Rockville, MD 20850, USA.

As a step toward propagation of synthetic genomes, we completely replaced the genome of a bacterial cell with one from another species by transplanting a whole genome as naked DNA. Intact genomic DNA from Mycoplasma mycoides large colony (LC), virtually free of protein, was transplanted into Mycoplasma capricolum cells by polyethylene glycol-mediated transformation. Cells selected for tetracycline resistance, carried by the M. mycoides LC chromosome, contain the complete donor genome and are free of detectable recipient genomic sequences. These cells that result from genome transplantation are phenotypically identical to the M. mycoides LC donor strain as judged by several criteria.

Genome transplant makes species switch
One type of bacterium has been reprogrammed into another.
Philip Ball

By transplanting their genomes, US scientists have converted one species into another.

John Glass and his co-workers at the J. Craig Venter Institute in Rockville, Maryland, have taken DNA from a bacterium called Mycoplasma mycoides and inserted it into cells of the closely related species Mycoplasma capricolum.

They find that the recipient cells with the new genome behave like those of the donor species, making protein molecules characteristic of the donor. It’s like re-booting a cell with a new operating system, says Glass.

“The method is very impressive,” says biomedical engineer Jim Collins of Boston University. “It’s surprising that they could get such a large piece of DNA into the bugs, and even more surprising that they could get the new genome jump-started.”

To swap the genomes, the researchers encased M. mycoides cells in a gel and used enzymes to break them apart and destroy their proteins, leaving only their naked DNA.

They mixed this DNA into colonies of M. capricolum and added a chemical that makes cells fuse together. The researchers suspect that some of the recipient cells fused around the naked donor genomes, producing cells with both species’ DNA.

When these hybrids divide, one genome ends up in each daughter cell. The donor M. mycoides genome contained a gene conferring resistance to a specific antibiotic, a dose of which was used to kill off all the cells without the donor genome.

The two species’ genomes are only about 75% identical. So it wasn’t obvious that M. capricolum’s machinery for reading and acting on genetic instructions would also work for M. mycoides.

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