Shapiro redux: experiments with minimal genes forms (Introduction)

by David Turell , Wednesday, August 09, 2023, 17:44 (470 days ago) @ David Turell

They evolve:

https://www.quantamagazine.org/even-synthetic-life-forms-with-a-tiny-genome-can-evolve-...

"Seven years ago, researchers showed that they could strip cells down to their barest fundamentals, creating a life form with the smallest genome that still allowed it to grow and divide in the lab. But in shedding half its genetic load, that “minimal” cell also lost some of the hardiness and adaptability that natural life evolved over billions of years. That left biologists wondering whether the reduction might have been a one-way trip: In pruning the cells down to their bare essentials, had they left the cells incapable of evolving because they could not survive a change in even one more gene?

"Now we have proof that even one of the weakest, simplest self-replicating organisms on the planet can adapt. During just 300 days of evolution in the lab, the generational equivalent of 40,000 human years, measly minimal cells regained all the fitness they had sacrificed, a team at Indiana University recently reported in the journal Nature. The researchers found that the cells responded to selection pressures about as well as the tiny bacteria from which they were derived. A second research group at the University of California, San Diego came to a similar conclusion independently in work that has been accepted for publication.

“'It turns out life, even such simple wimpy life as a minimal cell, is much more robust than we thought,” said Kate Adamala, a biochemist and assistant professor at the University of Minnesota who was not involved in either study. “You can throw rocks at it, and it’s still going to survive.” Even in a genome where every single gene serves a purpose, and a change would seemingly be detrimental, evolution molds organisms adaptively.

“'It’s a stunning achievement,” said Roseanna Zia, a physicist at the University of Missouri whose research aims to build a physics-based model of a minimal cell and who was not involved in the study. The new work showed that even without any genome resources to spare, she said, the minimal cells could increase their fitness with random changes in essential genes.

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"They calculated that the original minimal cell had lost 53% of its relative fitness along with its nonessential genes. The minimization had “made the cell sick,” Lennon said. Yet by the end of the experiments, the minimal cells had evolved all that fitness back. They could go toe-to-toe against the ancestral bacteria.

“'That blew my mind,” said Anthony Vecchiarelli, a microbiologist at the University of Michigan who was not involved in the study. “You would think that if you have only essential genes, now you’ve really limited the amount of evolution that … can go in the positive direction.”

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"When Lennon and Moger-Reischer adjusted for the relative fitness of the organisms, they found that the minimal cells evolved 39% faster than the synthetic M. mycoides bacteria from which they were derived.

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"The researchers found that most of the beneficial mutations favored by natural selection in their experiments were in essential genes. But one critical mutation was in a nonessential gene called ftsZ, which codes for a protein that regulates cell division. When it mutated in M. mycoides, the bacterium grew 80% larger. Curiously, the same mutation in the minimal cell didn’t increase its size. That shows how mutations can have different functions depending on the cellular context, Lennon said. (my bold)

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"'They observed a “fear-greed trade-off,” a tendency also seen in natural bacteria to evolve mutations in genes that will help it grow rather than mutations that would produce more DNA repair proteins to correct the errors." (my bold)

Comment: pure experimentation in a Shapiro mold. My first bold notes the use of natural selection to explain the issue, when we know bacteria can edit DNA, not natural selection. The second bold shows they recognized Shapiro's work.