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Mechanisms of nucleic acid accumulation were likely critical to life's emergence in the ferruginous oceans of the early Earth. How exactly prebiotic geological settings accumulated nucleic acids from dilute aqueous solutions, is poorly understood. As a possible solution to this concentration problem, we simulated the conditions of prebiotic low‐temperature alkaline hydrothermal vents in co‐precipitation experiments to investigate the potential of ferruginous chemical gardens to accumulate nucleic acids via sorption. The injection of an alkaline solution into an artificial ferruginous solution under anoxic conditions (O2 < 0.01% of present atmospheric levels) and at ambient temperatures, caused the precipitation of amakinite ("white rust"), which quickly converted to chloride‐containing fougerite ("green rust"). RNA was only extractable from the ferruginous solution in the presence of a phosphate buffer, suggesting RNA in solution was bound to Fe2+ ions. During chimney formation, this iron‐bound RNA rapidly accumulated in the white and green rust chimney structure from the surrounding ferruginous solution at the fastest rates in the initial white rust phase and correspondingly slower rates in the following green rust phase. This represents a new mechanism for nucleic acid accumulation in the ferruginous oceans of the early Earth, in addition to wet‐dry cycles and may have helped to concentrate RNA in a dilute prebiotic ocean. [ABSTRACT FROM AUTHOR]

The emergence of functional oligonucleotides on early Earth required a molecular selection mechanism to screen for specific sequences with prebiotic functions. Cyclic processes such as daily temperature oscillations were ubiquitous in this environment and could trigger oligonucleotide phase separation. Here, we propose sequence selection based on phase separation cycles realized through sedimentation in a system subjected to the feeding of oligonucleotides. Using theory and experiments with DNA, we show sequence-specific enrichment in the sedimented dense phase, in particular of short 22-mer DNA sequences. The underlying mechanism selects for complementarity, as it enriches sequences that tightly interact in the dense phase through base-pairing. Our mechanism also enables initially weakly biased pools to enhance their sequence bias or to replace the previously most abundant sequences as the cycles progress. Our findings provide an example of a selection mechanism that may have eased screening for auto-catalytic self-replicating oligonucleotides. [ABSTRACT FROM AUTHOR]

Silicate glasses are ubiquitous on terrestrial planets wherever molten rock - generated by volcanism or impacts - is quenched by air or water. Hence, they provided ready and abundant reactive solid surfaces for prebiotic chemistry on the early Earth. Here, we show that rock glass composition determines basicity, which in turn modulates the outcome of prebiotic synthetic processes such as the polymerization of 3', 5' cyclic guanosine monophosphate. [ABSTRACT FROM AUTHOR]

Life is based on informational polymers such as DNA or RNA. For their polymerization, high concentrations of complex monomer building blocks are required. Therefore, the dilution by diffusion poses a major problem before early life could establish a non-equilibrium of compartmentalization. Here, we explored a natural non-equilibrium habitat to polymerize RNA and DNA. A heat flux across thin rock cracks is shown to accumulate and maintain nucleotides. This boosts the polymerization to RNA and DNA inside the crack. Moreover, the polymers remain localized, aiding both the creation of longer polymers and fostering downstream evolutionary steps. In a closed system, we found single nucleotides concentrate 104-fold at the bottom of the crack compared to the top after 24 hours. We detected enhanced polymerization for 2 different activation chemistries: aminoimidazole-activated DNA nucleotides and 2′,3′-cyclic RNA nucleotides. The copolymerization of 2′,3′-cGMP and 2′,3′-cCMP in the thermal pore showed an increased heterogeneity in sequence composition compared to isothermal drying. Finite element models unravelled the combined polymerization and accumulation kinetics and indicated that the escape of the nucleotides from such a crack is negligible over a time span of years. The thermal non-equilibrium habitat establishes a cell-like compartment that actively accumulates nucleotides for polymerization and traps the resulting oligomers. We argue that the setting creates a pre-cellular non-equilibrium steady state for the first steps of molecular evolution. [ABSTRACT FROM AUTHOR]

For the emergence of life, the abiotic synthesis of RNA from its monomers is a central step. We found that in alkaline, drying conditions in bulk and at heated air‐water interfaces, 2′,3′‐cyclic nucleotides oligomerised without additional catalyst, forming up to 10‐mers within a day. The oligomerisation proceeded at a pH range of 7–12, at temperatures between 40–80 °C and was marginally enhanced by K+ ions. Among the canonical ribonucleotides, cGMP oligomerised most efficiently. Quantification was performed using HPLC coupled to ESI‐TOF by fitting the isotope distribution to the mass spectra. Our study suggests a oligomerisation mechanism where cGMP aids the incorporation of the relatively unreactive nucleotides C, A and U. The 2′,3′‐cyclic ribonucleotides are byproducts of prebiotic phosphorylation, nucleotide syntheses and RNA hydrolysis, indicating direct recycling pathways. The simple reaction condition offers a plausible entry point for RNA to the evolution of life on early Earth. [ABSTRACT FROM AUTHOR]

The assembly of ancient informational polymers from nucleotide precursors is the central challenge of life's origin on our planet. Among the possible solutions, dry polymerization of 3',5'‐cyclic guanosine monophosphate (3',5'‐cGMP) has been proposed as a candidate to create oligonucleotides of 15–20 units in length. However, the reported sensitivity of the reaction to the presence of cations raised questions of whether this chemistry could be relevant in a geological context. The experiments in this study show that the presence of cations is not restrictive as long as the reaction is conducted in an acidic environment, in contrast to previous reports that suggested optimal conditions at pH 9. [ABSTRACT FROM AUTHOR]

Previous studies on the polymerization of 3',5' cyclic guanosine monophosphate (cGMP) demonstrated the potential of the compound in the abiotic generation of the first oligonucleotide sequences on the early Earth. These experiments were conducted under idealized laboratory conditions, which logically raises the question whether the same chemistry could take place in the harsh environment present on our planet in its earliest days. In the current study, we focus on the mineralogical context of this chemistry and show that numerous, but not all, common minerals assumed to be present on the early Earth could host the polymerization of H‐form 3',5' cGMP. In particular, we have found that quartz varieties are especially suitable for this purpose, similar to andalusite, amphibole or micas. On the contrary, olivine, calcite, and serpentine‐group minerals interfere with the studied polymerization chemistry. Our results show that crystallization on mineral surfaces, which is mainly a diffusion controlled process, determines the ability of 3',5' cGMP to polymerize. The observation that numerous amorphous and crystalline SiO2 forms are compatible with the oligomerization chemistry suggests that the process could commonly occur in a wide range of primordial environments allowing for crystallization of the cyclic monomers from a dropping solution. [ABSTRACT FROM AUTHOR]

Microbial fossils preserved by early diagenetic chert provide a window into the Proterozoic biosphere, but seawater chemistry, microbial processes, and the interactions between microbes and the environment that contributed to this preservation are not well constrained. Here, we use fossilization experiments to explore the processes that preserve marine cyanobacterial biofilms by the precipitation of amorphous silica in a seawater medium that is analogous to Proterozoic seawater. These experiments demonstrate that the exceptional silicification of benthic marine cyanobacteria analogous to the oldest diagnostic cyanobacterial fossils requires interactions among extracellular polymeric substances (EPS), photosynthetically induced pH changes, magnesium cations (Mg2+), and >70 ppm silica. [ABSTRACT FROM AUTHOR]

Microscale thermophoresis (MST) is a versatile technique to measure binding affinities of binder–ligand systems, based on the directional movement of molecules in a temperature gradient. We extended MST to measure binding kinetics as well as binding affinity in a single experiment by increasing the thermal dissipation of the sample. The kinetic relaxation fingerprints were derived from the fluorescence changes during thermodynamic re‐equilibration of the sample after local heating. Using this method, we measured DNA hybridization on‐rates and off‐rates in the range 104–106 m−1 s−1 and 10−4–10−1 s−1, respectively. We observed the expected exponential dependence of the DNA hybridization off‐rates on salt concentration, strand length and inverse temperature. The measured on‐rates showed a linear dependence on salt concentration and weak dependence on strand length and temperature. For biomolecular interactions with large enthalpic contributions, the kinetic MST technique offers a robust, cost‐effective and immobilization‐free determination of kinetic rates and binding affinity simultaneously, even in crowded solutions. [ABSTRACT FROM AUTHOR]

All life on Earth is built of organic molecules, so the primordial sources of reduced carbon remain a major open question in studies of the origin of life. A variant of the alkaline-hydrothermal-vent theory for life's emergence suggests that organics could have been produced by the reduction of CO2 via H2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog-and proposed evolutionary predecessor-of the Wood-Ljungdahl acetyl-CoA pathway of modern archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO2 with H2 to formate (HCOO-), which has proven elusive in mild abiotic settings. Here we show the reduction of CO2 with H2 at room temperature under moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labeling with 13C confirmed formate production. Separately, deuterium (2H) labeling indicated that electron transfer to CO2 does not occur via direct hydrogenation with H2 but instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly, removing H2, or eliminating the precipitate yielded no detectable product. Our work demonstrates the feasibility of spatially separated yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches. [ABSTRACT FROM AUTHOR]

Unilamellar lipid vesicles can serve as model for protocells. We present a vesicle fission mechanism in a thermal gradient under flow in a convection chamber, where vesicles cycle cold and hot regions periodically. Crucial to obtain fission of the vesicles in this scenario is a temperature-induced membrane phase transition that vesicles experience multiple times. We model the temperature gradient of the chamber with a capillary to study single vesicles on their way through the temperature gradient in an external field of shear forces. Starting in the gel-like phase the spherical vesicles are heated above their main melting temperature resulting in a dumbbell-deformation. Further downstream a temperature drop below the transition temperature induces splitting of the vesicles without further physical or chemical intervention. This mechanism also holds for less cooperative systems, as shown here for a lipid alloy with a broad transition temperature width of 8 K. We find a critical tether length that can be understood from the transition width and the locally applied temperature gradient. This combination of a temperature-induced membrane phase transition and realistic flow scenarios as given e.g. in a white smoker enable a fission mechanism that can contribute to the understanding of more advanced protocell cycles. [ABSTRACT FROM AUTHOR]

We show how fluid can be moved by a laser scanning microscope. Selected parts of a fluid film are pumped along the path of a moving warm spot which is generated by the repetitive motion of an infrared laser focus. With this technique, we remotely drive arbitrary two-dimensional fluid flow patterns with a resolution of 2 μm. Pump speeds of 150 μm/s are reached in water with a maximal temperature increase in the local spot of 10 K. Various experiments confirm that the fluid motion results from the dynamic thermal expansion in a gradient of viscosity. The viscosity in the spot is reduced by its enhanced temperature. This leads to a broken symmetry between thermal expansion and thermal contraction in the front and the wake of the spot. As result the fluid moves opposite to the spot direction due to both the asymmetric thermal expansion in the spot front and the asymmetric thermal contraction in its wake. We derive an analytical expression for the fluid speed from the Navier–Stokes equations. Its predictions are experimentally confirmed without fitting parameters under a number of different conditions. In water, this nonlinearity leads to a fluid step of <100 nm for each passage of the spot. Since the spot movement can be repeated in the kilohertz regime, fluid speeds can exceed 100 μm/s. Using this technique, we pump nanoparticles over millimeters through a gel. An all-optical creation of a dilution series of DNA and biomolecules by aliquotation and mixing is demonstrated for fluids sandwiched between untreated and unstructured, disposable microscope cover slips. The shown optical remote control of fluid flow expands the microfluidic paradigm into previously inaccessible regimes of tiny volumes, closed flow paths, fast switching between flow patterns, and remote fluid control under extreme fluid conditions. [ABSTRACT FROM AUTHOR]

To understand the emergence of life, a better understanding of the physical chemistry of primordial non‐equilibrium conditions is essential. Significant salt concentrations are required for the catalytic function of RNA. The separation of oligonucleotides into single strands is a difficult problem as the hydrolysis of RNA becomes a limiting factor at high temperatures. Salt concentrations modulate the melting of DNA or RNA, and its periodic modulation would enable melting and annealing cycles at low temperatures. In our experiments, a moderate temperature difference created a miniaturized water cycle, resulting in fluctuations in salt concentration, leading to melting of oligonucleotides at temperatures 20 °C below the melting temperature. This would enable the reshuffling of duplex oligonucleotides, necessary for ligation chain replication. The findings suggest an autonomous route to overcome the strand‐separation problem of non‐enzymatic replication in early evolution. [ABSTRACT FROM AUTHOR]