Single-celled life forms need only the simplest evolutionary foothold to gain a foothold in their environment.
Even an extremely minimal cell containing just 493 genes can mutate and adapt to improve its fitness, researchers say — a critical step in the persistence and stability of life now demonstrated in the lab.
The insights come from a new study by a team of researchers from the US and Brazil, who stripped a cell of all but the essential genes to see if it could still evolve.
The cell is an artificially streamlined version of Mycoplasma mycoides – a parasitic bacteria found in the intestines of goats and other ruminants.
Over time, as this parasite became dependent on its host for survival, it lost many of its original genes.
Today, it has only 901 left in its genome, which is small compared to the thousands of genes that code for proteins in many other bacterial species, or even the tens of thousands found in plants and animals.
Then scientists eliminated another 41 percent synthetically M. mycoides’ genes, leaving behind all but the most essential sequences, they created a free-living cell with the smallest genome of any organism grown in pure culture.
According to Indiana University biologist Jay Lennon, the edited bacteria has the name M. mycoides JCVI-syn3B – represents the bare bones of what is needed for a cell to survive.
“You might assume there’s no wiggle room for mutations,” say Lennon, “which could limit his potential to evolve.”
But even this skeleton can do more than you might think.
“We can simplify [the cell] to the bare necessities,” explains Lennon, “but that doesn’t stop evolution from working.”
When Lennon and his colleagues allowed it M. mycoides Growing JCVI-syn3B in the lab for 300 days (equivalent to 2,000 bacterial generations), they found an exceptionally high mutation rate for such a simple cell.
Compared to the original M. mycoidesthis new species evolved 39 percent faster and regained all the fitness it lost when researchers artificially removed many of its genes.
When placed in the same test tube as other minimal cells that had not evolved for 300 days, the evolved cells outnumbered the others, took over and became the most dominant species. It clearly suited its surroundings better.
“Our findings show that natural selection can rapidly improve the fitness of one of the simplest autonomously growing organisms,” said Lennon and colleagues. to write.
Theoretically, the larger a cell is, the more complexity it can hold. Surprisingly, the evolved cells did not grow in physical size. The researchers suspect this is because half of the membrane proteins have been removed, meaning the cell lacked the means to expand its volume.
While there are many nuances left to explore, including which genes evolved and why, the findings suggest that natural selection is powerful enough to optimize even the simplest single-celled organisms.
In other words, the authors to conclude“it shows that life finds a way.”
The study is published in Nature.