Ursuppe on the seabed?

High concentration of biomolecules at hydrothermal sources possible

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How and where did the first life on earth originate? The Ursuppe of the oceans about four million years ago is considered to be the origin of the first life forms can prove so far, however, not. However, an international research team has actually discovered that in the pore system of hydrothermal vents on the seafloor, a high concentration of biomolecules can occur locally due to the large temperature differences. They report here in the journal PNAS.

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At the ocean floor there are hydrothermal springs, from which several hundred degrees of hot water escape. Discovered only a few decades ago, they were initially considered extremely hostile to the environment - until complex ecosystems at these sources were detected. Increasingly, there were also theories according to which life could have originated from these sources. "However, all theoretical and experimental approaches to the biochemical origin of life require a high initial concentration of biomolecules, " reports Dieter Braun, head of an Emmy Noether junior research group at the Chair of Applied Physics, Ludwig Maximilian University (LMU) Munich. "So far, it was unclear what natural mechanism would have made this possible in the early oceans, in which even the simplest compounds have been severely diluted."

Accumulation of biomolecules

In collaboration with other LMU researchers and international scientists, he has now been able to provide a possible solution to this concentration problem: "In the extensive pore systems of the hydrothermal sources, a mechanism is involved that allows extreme accumulation of biomolecules, " said Braun. In the porous rock near hydrothermal sources, high temperature gradients occur. A simulation of the processes by Braun and his co-workers Philipp Baaske showed that even small biomolecules can be accumulated to a high degree in these elongated pores, which are only a few hundred microns in size. "The large differences in temperature drive two effects, convection and thermophoresis, " explains Baaske. "In combination, they can cause a greatly increased concentration of biomolecules at the bottom of the pore. This mechanism is also known as a gas separation tube or Clusius tube and has been used experimentally, among other things, for isotope separation of uranium. "

Many theories on the origin of life build on the fact that initially short molecules of RNA, a nucleic acid closely related to the DNA molecule, replicate each other. However, according to previous knowledge, the concentration of the molecule necessary for such an "RNA world" was nowhere to be found on earth. "However, our work has now shown that it is precisely such small compounds as the short RNA molecules that can be accumulated to a high degree in hydrothermal sources, " says Braun. "An optimal concentration of RNA is achieved in pores with a width of 0.15 millimeters and a length of about 40 millimeters. In the process, the molecules accumulate in an area roughly the size of modern cells. "In smaller pores, on the other hand, longer molecules accumulate better. This mechanism can also be used in biotechnology, for example, to concentrate molecules from biological and medical samples. display

Molecular evolution

The pores are similar in their effect to a kind of molecular trap that sufficiently concentrates small biomolecules and accumulates exponentially longer compounds. This creates a natural selection pressure of accumulation in favor of larger molecules. That would be a helpful effect especially in molecular evolution, because more and more information can be placed on the connections. At the same time, the larger molecules are increasingly prevented from spreading in the surrounding seawater. "All in all, the hydrothermal pores can be understood as selective molecular traps especially for the most evolutionarily interesting molecules, " says Baaske.

This new insight was only possible thanks to close interdisciplinary collaboration between physicists, biochemists and geologists, including Kono H. Lemke of the Swiss Federal Institute of Technology (ETH) in Zurich, and Michael J. Russell of the Jet Propulsion Laboratory in Pasadena, California. one of the leading specialists in the field of hydrothermal springs. As Braun has already demonstrated in previous work and has been confirmed in independent studies, the temperature differences in the hydrothermal sources can also drive one of the most important biochemical reactions: the polymerase chain reaction, PCR for short, for multiplication Compensation of genetic information. Thus, it seems easy to imagine that parallel to the accumulation first thermally driven replication reactions took place - initially probably with the help of catalytically active RNA molecules instead of the highly developed enzyme polymerase, which now promotes this reaction in nature and also in research laboratories this function takes over.

Until now, it has not been possible to construct a realistic experimental chain from the conditions on the still young earth to the first replicating and evolving molecules - not least because of the open question of the concentration of biomolecules. "Our work has demonstrated for the first time a realistic possibility for high accumulation, " says Braun. It shows once again that the interdisciplinary approaches, which are particularly supported and pursued by LMU's Center for NanoScience (CeNS), lead to far-reaching results can. Although our results can not provide sufficient evidence for the origin of life in the hydrothermal vents, we may be very much concerned with the solution of this problem come closer.

(Ludwig-Maximilians-University Munich, 11.05.2007 - AHE)