How life emerged is a long standing problem of science. That it could not be resolved yet, sparked concern that science and especially biology is not yet complete. We performed highly diverse experiments that explore physical non-equilibria to bring about prebiotic reactions to now much better understand how Darwinian evolution could be triggered on an early Earth and how these reactions gave rise to an ever increasing complexification of biological information.
For this, we either focused on creating a most simple RNA world where a low number of molecules, in our case only two nucleotides of RNA, would trigger the evolution of sequence information. We found that at alkaline conditions, these molecules trigger ring opening polymerization of short random sequences, if they were activated by 2’,3’-cyclic phosphates. The usage of elevated pH at dry conditions without buffering molecules enabled a most simple and start of biological molecules by wet-dry cycling at room temperature. Very interestingly, the same conditions in wet state triggered an albeit slow, but highly precise replication reaction by templated ligation. In nature, this reaction cascade would be triggered by the low salt wet state in morning dew that separated the RNA strands, which would increase salt concentrations as the humidity drops over the course of the day, triggering replication by ligation and lead to a dry state at noon, which would polymerize again the raw material for the next cycle. Recycling is very natural since the hydrolysis of RNA leads again to the 2’,3’-cyclic phosphate ends of RNA.
On the other hand, we explored geological settings such as hydrothermal vents, but also looked into long-term evolution of replicating processes, by either templated ligation or templated polymerization with the use of proteins which speed up the reactions. Sequencing was established for these reactions and we found autocatalytic loops in templated ligation and the formation of long strands in templated polymerization. We could also show that Ribozymes flourish under the air-water interface conditions which were speeding up replication and selection reactions. What was most exciting was that the same settings which were very good for RNA evolution also triggered the accumulation of modern biochemistry in the form of cell-free extracts. These materials are basically the inner molecule mix of cells which are very sensitive to conditions. However, we found that both thermophoretic accumulation and accumulation at heated air-water interfaces triggered their coordinated accumulation and constituted a cellular state without cells and without membranes, offering a completely new way to think about synthetic cells in the future.
As a result, we now see new ways of life to emerge and we think the hard hurdles are overcome. The fog is lifting and straight forward experiments become clear now to demonstrate in ever more detail how some initially lonely molecules could create an autocatalytic process of sequence replication that brought about the wonders of life onto an early Earth – and possibly also to other planets.
