In the beginning there was the vesicle: A self-generated bubble with a membrane consisting of a lipid bilayer, formed by compounds which existed on the very young earth, in a two-phase solvent system consisting of water and CO2. It is surrounded by a range of different peptides, plus temperatures of 40 to 80°C and an elevated pressure of 60 to 80 bar. Those are the conditions as they existed some 3.8 billion years ago and still do today – far down in the earth's crust, at a depth of about one kilometer.
With this experimental setup, chemist Christian Mayer from the Center for Nanointegration and geologist Ulrich Schreiber, also a professor at the UDE, have simulated water-filled crevices in the earth's bowels as well as geothermal sources. In their laboratory experiment, they regularly changed the pressure in the system at 20-minute intervals, thereby changing the quality of the solvent, as it also occurs in nature through tidal forces and geysers. In the process, the vesicles were periodically destroyed and re-formed. Thus, a total of 1,500 generations of vesicles were created and disintegrated again within two weeks.
Forwarding Functions to Subsequent Generations
The researchers discovered that an increasing number of vesicles survived the generation change. Analyses showed that these vesicles had embedded specific sequences of 10 to 12 amino acids from the pool of possible peptides into their membrane in a cluster-like manner. Further tests, specifically carried out with one of these peptides, revealed three effects on the vesicles in question: They became thermally more stable, smaller and hence more resistant and – most importantly – the permeability of their membrane was considerably increased.
"We have concluded that the peptide clusters in the membrane have formed first channel structures. This enables the vesicles to balance the osmotic pressure," explained Mayer. "All the effects mentioned are survival strategies, if you will." Peptide and vesicles stabilize each other. But even if such a structure is destroyed after a few cycles in the end, the following generations take up the peptide structure and integrate it into their membrane again. In this way, a function is passed on through the molecular pool and further developed in the course of evolution, just like it happens in the horizontal gene transfer between bacteria.
NASA's Definition of Life Already Met in the Lab
At least according to the very generous definition of the US space agency NASA, this is already a kind of life. For some astrobiologists already consider a system to be alive if it is capable of any kind of evolution. However, according to the biological definition, which has so far been limited to terrestrial life forms, essential points on the checklist, such as metabolism, reproduction and growth, are still missing.
However, Mayer and Schreiber are certain that the experiments have at least shown a way to a primitive preliminary stage of life. "As we have simulated in time-lapse, functions could have been created billions of years ago that made such vesicles stable enough to come to the surface from the depths, for example with the flow of tectonic fluids or during geyser eruptions," said Schreiber.
Subsequently, a first metabolism with concentration gradients as an energy source could have developed. If the ability to self-replicate is eventually acquired, then even from a biological point of view an inanimate component slowly becomes a living organism, a first cell.
„The First Cell“ Comes out in July
With the exception of the theory that life came to earth on meteorites, the thesis of Mayer and Schreiber is in line with common assumptions about the origin of life. Mayer summarizes: "We assume, that this kind of molecular evolution in the depths took place parallel to other mechanisms or temporally displaced from them."
Mayer and Schreiber's book"The First Cell – The Mystery Surrounding the Beginning of Life"will be published in July 2020.