Yeast cells
Cells of the yeast species Saccharomyces cerevisiae. Wikimedia Commons

A team of international researchers has taken a significant step toward the creation of fully synthetic organisms. In seven papers published Thursday in the journal Science, researchers from the Synthetic Yeast 2.0 (Sc2.0) collaboration describe the creation of five additional “designer” chromosomes of baker’s yeast (Saccharomyces cerevisiae), bringing the total number of artificial yeast chromosomes to six.

Eventually, the collaboration, which includes over 200 researchers, hopes to design, build and integrate into the cells all 16 of yeast’s chromosomes.

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“This work sets the stage for completion of designer, synthetic genomes to address unmet needs in medicine and industry,” Jef Boeke, the Sc2.0 project director, said in a statement. “Beyond any one application, the papers confirm that newly created systems and software can answer basic questions about the nature of genetic machinery by reprogramming chromosomes in living cells.”

Chromosomes are molecular structures that contain an organism’s genetic material, which is encoded in four base pairs of the DNA. In eukaryotic organisms like yeasts, these chromosomes are packaged inside the cell’s nucleus.

In order to create and test artificial yeast chromosomes, the researchers proceeded in a step-by-step fashion. The first step involved copying DNA sequence already present in yeast (leaving out the so-called junk DNA that, to our best knowledge, does not serve any purpose). Next, they synthesized these DNA sequences in labs and proceeded to integrate them into yeast cells — replacing the organism’s natural chromosomes.

All the chromosomes assembled in labs were integrated into yeast cells and were found to function normally. Surprisingly, the yeast cells still grew normally even though the synthetic chromosomes were not exact copies of their natural counterparts.

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“It seems like we can really kind of torture the genome in complicated ways and frequently the yeast shrugs its shoulders and grows like normal,” Boeke told Nature News.

The quest to create synthetic life — which began in earnest in 2010 when scientists at the J. Craig Venter Institute created a bacterium controlled by a synthetic genome — is more than just a purely academic one (although it would provide crucial insights into how human cells work). Such cells, if created, could serve as mini-factories for the manufacture of new drugs and biofuels.

In 2014, when the same collaboration synthesized the first function yeast chromosome, Boeke likened the ability to manipulate the yeast genome to shuffling a deck of cards — with each gene being a card.

“We can pull together any group of cards, shuffle the order and make millions and millions of different decks, all in one small tube of yeast,” Boeke said in a statement. “Now that we can shuffle the genomic deck, it will allow us to ask, can we make a deck of cards with a better hand for making yeast survive under any of a multitude of conditions, such as tolerating higher alcohol levels.”