Astronomer Fred Hoyle famously quipped in 1982 that the odds of a simple living thing assembling itself from inanimate chemicals were as slim as the chance that a tornado passing through a junkyard would leave in its wake a Boeing 747.
The statement reflects the 20th-century understanding that even pond scum was composed of cells of mind-boggling complexity. Today biologists believe that modern cells evolved from much simpler ancestors — organisms that no longer exist.
Now scientists have used genetic manipulation to create something of a throwback: a new organism, simpler than any known in nature today. They started with a relatively simple bacterium, Mycoplasma mycoides, and then pared down its genome to about half the original size. The scientists dubbed the new organism JCVI-syn3.0, after the institute started by the group’s leader, J. Craig Venter. They announced it Thursday in Science.
In 2010, the same group showed they could start with vats of chemicals, synthesize an entire genome, transfer it into a cell that had had its own genes removed, and watch the bug “boot up” and start replicating itself. That bug, JCVI-syn1.0, shattered any illusion that there’s a mystical boundary between chemistry and life. This week’s new life form shatters another illusion: that life on earth has always been complex.
JCVI-syn3.0, with a total of 473 genes, is the closest that scientists have ever come to understanding the workings of every gene in one organism, said team co-leader Clyde Hutchison. That’s impressed biologists and bioengineers.
“Only when you try to build something do you find out what’s truly required,” said Drew Endy, an expert in the emerging field of synthetic biology. “Synthesis of DNA, genomes and now entire cells is increasingly turning into a boon for understanding how life works.”
The creators are quick to point out that JCVI-syn3.0 is not a representative of an ancestral form of life. The bug they started with appears to have evolved from more complex ancestors and became simpler to adapt to life as a parasite. (It lives in cows and other ruminant animals.) To simplify it further, the researchers systematically destroyed each gene to figure out whether it was essential to survival.
One surprise was that a third of the genes that proved to be essential don’t have a clearly known function. Another surprise was that there was not one unique set of essential genes. In many cases, they could knock out gene A, or gene B, and the organism would survive, but would die if both were destroyed.
If there is an absolute minimum genome it might have just one gene, said Harvard biologist George Church, pointing to the research into the origin of life being led by biologist Jack Szostak.
Szostak is looking from the very bottom up, at ways that chemicals could come together to form very primitive cells. Scientists have already shown that it’s possible for chemical reactions to form the building blocks of RNA — a code-carrying relative of DNA. And they’re getting close to figuring out how those individual code letters might start to stick together.
We’ve come a long way since the 20th-century advent of genetic engineering — which allowed people to transfer genes from one organism to another. The 21st century has brought a more precise version of genetic engineering known as gene editing. That’s brought on a burst of new ways to produce drugs and biofuels, alter agricultural products and laboratory animals, and, in theory if not yet in practice, prevent human disease.
When Hoyle came up with his 747 analogy, he wasn’t trying to argue for anything supernatural. He was promoting the idea that life came from outer space. Perhaps even if its origin were very unlikely, Hoyle reasoned, life had to start on only one of any of the billions of planets in the universe. From there it might have evolved into some sort of spore that traveled between the stars.
The idea has fallen out of favor now, though it’s not disproved. The origin of life on Earth remains unexplained, but this week we saw the notion of a simpler version of life go from theory to reality.
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