GM micro-organisms throw light on early evolution

Two new synthetic micro-organisms could help reveal how life on the planet evolved, say scientists at Scripps Research Institute in La Jolla, California, US.

Researchers are hoping a newly engineered bacterium and a genetically modified yeast will allow them to test the theory, developed in the 1960s, that says early life relied on RNA to store information before the evolution of DNA.

The work could also help explain the development of mitochondria – rod-shaped organelles that synthesise the chemicals that drive cellular metabolism.{%recommended 6469%}

“These engineered organisms will allow us to probe two key theories about major milestones in the evolution of living organisms – the transition from the RNA world to the DNA world and the transition from prokaryotes to eukaryotes with mitochondria,” says Peter Schultz , senior author on two linked papers published in the Journal of the American Chemical Society (JACS) and the Proceedings of the National Academy of Sciences (PNAS).

Prokaryotes, such as bacteria, are unicellular organisms that lack membrane-bound nuclei, mitochondria and other distinct organelles. They are thought to be the earliest forms of life. 

“Access to readily manipulated laboratory models enables us to seek answers to questions about early evolution that were previously intractable,” Schultz explains. 

The synthetic bacterium, a strain of E. coli, has a genome that contains up to 50% RNA and uses ribonucleotides to build its DNA, “thus simultaneously representing a new type of synthetic organism and possibly a throwback to billions of years ago”. 

“In science class,” says co-author Angad Mehta, “students learn that DNA leads to RNA which in turn leads to proteins – that’s a central dogma of biology – but the RNA world hypothesis turns that on its head. 

“For the RNA world hypothesis to be true, you have to somehow get from RNA to a DNA genome, yet how that might have happened is still a very big question among scientists.” 

He adds that the fact that the newly developed E. coli can survive and replicate could support the RNA theory.

The other microorganism is a yeast strain that uses bacteria that live inside it as its energy source, in a mechanism similar to the way mitochondria function. Mitochondria live inside cells and, among other tasks, supply energy to the cell. They have their own genomes, separate from the organism where they live. 

The researchers are hoping to evolve the bacteria in the yeast, also a strain of E. coli, into “mitochondria-like organelles”, which could help show how mitochondria came into being.