Researchers create living cells containing the smallest genome yet | March 28, 2016 Issue - Vol. 94 Issue 13 | Chemical & Engineering News
Volume 94 Issue 13 | p. 8 | News of The Week
Issue Date: March 28, 2016 | Web Date: March 25, 2016

Researchers create living cells containing the smallest genome yet

Minimal bacterial genome contains 473 genes, 149 of which still have unknown functions
Department: Science & Technology
News Channels: Biological SCENE
Keywords: synthetic biology, mycoplasma, minimal genome, microbiology
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The reduced genome (red circle) has about half the DNA base pairs of the starting genome (blue). The red bars inside the blue circle represent retained genome regions. The white numbers indicate genome segments.
Credit: Science
Graphic showing comparison of size of starting genome and reduced genome.
 
The reduced genome (red circle) has about half the DNA base pairs of the starting genome (blue). The red bars inside the blue circle represent retained genome regions. The white numbers indicate genome segments.
Credit: Science
[+]Enlarge
These cells contain a minimal bacterial genome with 473 genes, the smallest genome yet known. In this electron micrograph, the cells are magnified about 15,000 times.
Credit: Tom Deerinck and Mark Ellisman/National Center for Imaging and Microscopy Research/UC San Diego
Electron micrograph of cells containing a minimal bacterial genome.
 
These cells contain a minimal bacterial genome with 473 genes, the smallest genome yet known. In this electron micrograph, the cells are magnified about 15,000 times.
Credit: Tom Deerinck and Mark Ellisman/National Center for Imaging and Microscopy Research/UC San Diego

Researchers are a step closer to figuring out the minimum number of genes required to sustain life. Clyde A. Hutchison III and J. Craig Venter of the J. Craig Venter Institute, in La Jolla, Calif., and coworkers have designed and synthesized the smallest bacterial genome yet known (Science 2016, DOI: 10.1126/science.aad6253).

The researchers started with a genome they’d first synthesized in 2010, which contained 900 genes from the bacterium Mycoplasma mycoides (C&EN, May 24, 2010, page 10). They then used information from the biochemical literature to identify genes they could remove and still sustain bacterial life, forming a hypothetical “minimal genome.” But a genome produced from that design was a failure: When inserted into a recipient cell, it couldn’t sustain life.

After adding genes back in three more rounds of design and testing, the researchers ended up with a genome containing 473 genes that could form viable bacteria. They were surprised by how many “quasi-essential” genes they retained in the designer genome. Those genes weren’t necessary to keep the cell alive, but they were necessary for robust cell growth.

Christopher Voigt, an expert on synthetic biology at Massachusetts Institute of Technology, doesn’t know whether those genes needed for growth are significant. “It’s an open question whether an organism with a human-designed simplified genome can achieve the same growth as a natural one,” he says. “Is the inherent complexity a necessity, or is it disposable?”

Surprisingly, the researchers still don’t know the function of 149 genes in their designer genome. And that’s why robust growth wins out over an absolute minimum genome. “We’re interested in an organism with a workable growth rate so we can determine the functions of the remaining genes,” Hutchison says.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Erskien Lenier (March 24, 2016 7:22 PM)
How would they know they aren't creating an unstoppable lethal bacteria against humans or some other essential species to life on Earth? This seems as risky as the CERN mini black hole possibility that is an unpredictable variable so far. It would be one thing to do these experiments on the moon some place that could not contaminate our spaceship Earth. It seems irresponsible to do it here on Earth...
Celia Arnaud (March 28, 2016 6:58 AM)
I think the poor growth rate of this particular bacterium would suggest that's unlikely. But of course we can't say what would happen as it starts to evolve.
Charles E. (March 29, 2016 11:01 AM)
The fact that they're creating a minimalist lifeform significantly reduces the probability of virulence for an unstoppable lethal bacteria... They're attempting to identify the base genes required for life and what growth elements those genes confer in the cell. There's a much more likely chance of harm from bacteria that are naturally generating antibiotic resistance

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