Oparin never dreamed
Synthetic organisms have been created that will shed light on the course of evolution
Evgenia Efimova, Vesti
Evolution helps explain the diversity of life on Earth. Meanwhile, there are gaps in the knowledge of scientists about this process that they would like to fill.
To look into the past and look at some key stages in the development of life, scientists from the Scripps Institute have created synthetic microorganisms. According to the authors of the work, the resulting organisms may be similar to some creatures that could have inhabited the planet billions of years ago.
Experts have developed two types of synthetic microbes, each of which is designed to study different stages of evolution on Earth.
The first is a chimera bacterium, which has both RNA and DNA in its genome. It will help to understand how life was able to "ride" RNA and switch to using DNA molecules for its own purposes.
The second is a type of modified yeast with a symbiotic bacterium inside its cells. This organism should shed light on the appearance of mitochondria (recall that this is a kind of power plant of living cells). According to existing theories, mitochondria (which, by the way, have their own DNA) were introduced into ancient cells as symbiotic organisms, and then remained inside them, completely losing the ability to survive outside the host cell.
Synthetic microorganisms consist of yeast cells (blue) and bacteria (pink) inside the former. Both "elements" cannot survive without each other. Photo by Scripps Research Institute.
"Designed organisms allow us to study two key theories about the main milestones in the evolution of living organisms – the transition from the world of RNA to the world of DNA and the transition from prokaryotes to eukaryotes with mitochondria," says Peter Schultz, senior author of two papers.
The development and research of models that are easy to manipulate in the laboratory will allow scientists to look for answers to questions about early evolution, adds Schultz.
Recall that today life forms store their genetic information in DNA molecules. Meanwhile, scientists suggest that initially life could use simpler RNA molecules for the same purpose. And this was done until a certain stage in the development of life, when she began to use more stable DNA.
It remains a mystery when and how the "switch" occurred. It is possible that in the past there was an organism that used DNA and RNA at the same time.
This is exactly what scientists decided to test by developing a chimera bacterium to study its viability.
They modified E. coli (E. coli) so that it builds its DNA from ribonucleotides, which are commonly used to build RNA. The genome of the resulting microbes contained up to 50 percent RNA. The bacteria were able not only to survive, but also to multiply.
Experts plan to use the new organism to test other theories.
The second synthetic organism was developed to study the origin of mitochondria. They can be found in the cells of complex organisms called eukaryotes.
Essentially, mitochondria are the body's energy generators, converting oxygen into an adenosine triphosphate molecule.
Interestingly, there are indications that these organelles were once independent organisms that were slowly absorbed by more complex creatures. Mitochondria have their own DNA, and genetic analysis shows that they may be related to bacteria of the genus Rickettsia, which live inside the cells of host organisms.
To test whether bacteria can perform "mitochondrial duties" inside the cells of another organism, scientists again turned to E. coli and baker's yeast. They made them dependent on each other.
The bacteria were designed in such a way that they could not do without thiamine. They had to get this vitamin from yeast.
The latter were modified so that the existing mitochondria of yeast could not produce energy. In short, they had to rely on ATP molecules produced by bacteria.
It turned out that such an artificial symbiosis works. The bacteria not only survived, but also spawned more than 40 new generations without signs of slowing down. Moreover, they have even practically adapted to an unusual environment. It is suggested that they could eventually turn into something similar to mitochondria.
The authors intend to continue studying synthetic organisms of this kind in order to better understand the evolution of life on Earth.
New synthetic organisms are described in two articles published in PNAS and Journal of the American Chemical Society (Mehta et al., Engineering yeast endosymbions as a step towards the evolution of mitochondria and Bacterial Genome Containing Chimeric DNA–RNA Sequences).
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