LMU researchers discover a plausible geological constellation that could have triggered the origin of life on Earth

Munich, October 25, 2024 – The origin of life on Earth is still an unsolved mystery, but a common theory suggests that the replication of genetic material – the nucleic acids DNA and RNA – was a central and crucial process. RNA molecules can store genetic information and replicate themselves by forming double-stranded helices. The combination of these abilities enables them to mutate, evolve, adapt to different environments and ultimately encode the protein building blocks of life. To do this, the RNA strands must not only replicate to form a double strand, but also separate again to complete the replication cycle. However, the separation of the strands is a difficult task given the high salt and nucleic acid concentrations required for replication.

In a study published as a reviewed preprint in the journal eLife, a group of LMU researchers has now identified geological reaction conditions that could have triggered the emergence of life on Earth. A simple geophysical environment – a gas flow through a narrow water channel – can therefore create a physical environment that leads to the replication of nucleic acids.

‘So far, various mechanisms have been investigated for their potential to separate the DNA strands at the origin of life, but all require temperature changes that would lead to nucleic acid degradation,’ says lead author Philipp Schwintek, a PhD student in systems biophysics at LMU. ‘We investigated a simple scenario that is ubiquitous in geology: water flowing through a rock pore is dried by a gas that flows through the rock and reaches the surface. Such a scenario would have been very common on the volcanic islands of the early Earth, which provided the dry conditions necessary for RNA synthesis.

The team built a laboratory model of the rock pore with an upward flow of water that vaporises at an intersection with a vertical flow of gas, leading to an accumulation of dissolved molecules on the surface. At the same time, the gas flow creates a circular flow in the water, which drives the molecules back into the interior of the pore. To understand how this model affects the nucleic acids in the environment, the researchers observed the dynamics of the water flow using small beads and then tracked the movement of short, fluorescently labelled DNA fragments.

‘We had expected that continuous evaporation would lead to an accumulation of DNA strands at the interface,’ says Schwintek. ‘In fact, we found that the water at the interface evaporated continuously, but the nucleic acids in the aqueous surface accumulated near the gas-water interface.’ Within five minutes of starting the experiment, the DNA strands had tripled, while after one hour 30 times as many DNA strands had accumulated at the interface.

This indicates that the gas-water interface allows a sufficient concentration of nucleic acids for replication. However, the duplicate DNA strands must also be separated to complete a full replication cycle. This normally requires a change in temperature, but at constant temperature it requires a change in salt concentration.

‘We hypothesised that the circular fluid flow at the interface generated by the gas flow, together with passive diffusion, drives strand separation by forcing the nucleic acids through regions of different salt concentration,’ explains first author Dieter Braun, Professor of Systems Biophysics at LMU and member of the Origins Cluster of Excellence.

To test this, they used a method called FRET spectroscopy to measure the separation of the DNA strands – a high FRET signal indicates that the DNA strands are still connected, while a low FRET signal indicates that the strands are separated. As expected, the FRET signal initially increased near the gas-water interface, indicating the formation of double-stranded DNA.

However, later in the experiment, as the water flowed upwards, the FRET signal was weak – indicating single-stranded DNA. When the researchers overlaid this data with their simulation of water flow and salt concentration, they also found that the vortex at the gas-water interface caused changes up to three times the salt concentration, which could possibly lead to strand separation.

Although nucleic acids and salts accumulated near the gas-water interface, the concentrations of salt and nucleic acids in the bulk of the water remained negligible. This prompted the team to test whether the replication of nucleic acids could actually take place in this environment by adding fluorescent dye-labelled nucleic acids and an enzyme that can synthesise double-stranded DNA to the laboratory model of the rock pore. However, this enzyme requires the DNA strands to be separated again after each copying process, as it does not carry out this step itself. Normally, the temperature is briefly increased to separate the strands. In this experiment, however, the temperature was kept constant and the reaction was instead exposed to a combined flow of water and gas.

After two hours, the fluorescence signal had increased, indicating an increased number of replicated double-stranded DNA molecules. However, when gas and water were switched off, no increase in the fluorescence signal and therefore no increase in double-stranded DNA was observed.

‘In this work, we investigated a plausible and rich geological environment that could have triggered the replication of early life,’ Braun summarises. ‘We looked at an environment where gas flows over an open, water-filled rock pore without changing temperature and found that the combined flow of gas and water can trigger salt fluctuations that support DNA replication. Since this is a very simple geometry, our results greatly expand the repertoire of possible environments that could enable replication on early planets.’

Originalpublication:

Philipp Schwintek, Emre Eren, Christof Mast, Dieter Braun. Prebiotic gas flow environment enables isothermal nucleic acid replication. eLife 2024.
(https://doi.org/10.7554/eLife.100152.1)

ImageSource Archiv Stubaier Alpen