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There is a general assumption that amphiphilic compounds, such as fatty acids, readily form membranous vesicles when dispersed in aqueous phases. However, from earlier studies, it is known that vesicle stability depends strongly on pH, temperature, chain length, ionic concentration and the presence or absence of divalent cations. To test how robust...
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... the ionic solute concentrations of hydrothermal water taken from different sources in Yellowstone hydrothermal fields vary from micromolar to 27 mM total concentration of cations and anions (Table 2), and our results reported in Table 1 fall within this range. Second, the ionic solutes of seawater (Table 3) far exceed the highest concentrations of hydrothermal water. Such high concentrations inhibit membrane assembly and should be taken into account by proposals that life could begin in a marine environment. ...
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... Similar estimates exist for Archean terrestrial environments 48,49 , although there remains a paucity of data for concentrations of ionic species for the early Earth in general. Sensitivity of vesicles to salinity, has cast doubt on any oceanic environment as a possible origin of life location 50 . Recent work, however, has found that SCAs with novel headgroup moieties can withstand some more challenging conditions including high ionic strength and extremes of pH, particularly at acidic levels 51 . ...
Elucidating compositions of the first cell membranes requires experiments with molecules and chemical conditions representative of early Earth. The molecules used are described as ‘prebiotically plausible’, i.e., they could have formed through abiotic reactions before the emergence of biology. Similarly, the chemical properties of solutions in which these membranes are formed (e.g., pH, temperature, ionic strength) must represent early Earth environments. Here, using confocal and transmission electron microscopy combined with population morphometry, we show that prebiotically plausible molecules, in solutions representative of Hadean submarine alkaline hydrothermal vents, form microstructures with substantial morphological diversity. The microstructures hold the potential for use as analogues of prebiotic processes in the rock record. Additionally, many of the structures are morphologically similar to purported early microfossils, highlighting limitations of morphological interpretation in these studies. Detailed analyses of abiotic microstructures are essential for understanding the earliest life on Earth, and for interpretation of potential biosignatures from extra-terrestrial bodies.
... The structure of self-assembled fatty acids with encapsulated polymers is called a 'protocell'. The contents and morphology of individual protocells are unique in lab and field settings [7,27]. Some protocells have characteristics that make them more physically robust than others, which forms the conceptual basis for protocells to undergo a primitive version of natural selection at a macro-molecular scale. ...
... The solution was heated to ~40 °C and vortexed for 3 s. A 20 µL sample was dried on a microscope slide, then rehydrated with buffer to allow vesicles to encapsulate RNA [7,27]. After situating a cover slip on the slide, the preparation was photographed at 400× magnification. ...
... The hot spring scenario describes a land-based, volcanic hydrothermal field environment where cycles of evaporation and precipitation provide a mechanism for key prebiotic reactions, such as the synthesis and encapsulation of polymers inside membranous vesicles [7]. The resulting structures are referred to as 'protocells' (Figure 1) [7,27] and they can aggregate into proto-cellular networks that are speculated to be collectively capable of a primitive version of Darwinian Natural Selection and evolution based upon diversity and the differential survivability of protocells through environmental cycles [7,16]. Protocells are a leading model for the earliest phase of cellular life on Earth and potentially on similar planets, such as Mars. ...
Early Mars was likely habitable, but could life actually have started there? While cellular life emerged from prebiotic chemistry through a pre-Darwinian selection process relevant to both Earth and Mars, each planet posed unique selection ‘hurdles’ to this process. We focus on drivers of selection in prebiotic chemistry generic to Earth-like worlds and specific to Mars, such as an iron-rich surface. Iron, calcium, and magnesium cations are abundant in hydrothermal settings on Earth and Mars, a promising environment for an origin of life. We investigated the impact of cations on the stability and disruption of different primitive cell membranes under different pH conditions. The relative destabilizing effect of cations on membranes observed in this study is Ca2+ > Fe2+ > Mg2+. Cation concentrations in Earth systems today are too low to disrupt primitive membranes, but on Mars concentrations could have been elevated enough to disrupt membranes during surface dehydration. Membranes and RNA interact during dehydration–rehydration cycles to mutually stabilize each other in cation-rich solutions, and optimal membrane composition can be ‘selected’ by environmental factors such as pH and cation concentrations. We introduce an approach that considers how life may have evolved differently under the Martian planetary conditions and selective pressures.
... We envision that RNA-membrane interactions could modulate both the extent of flocculation and the permeability of the flocculated vesicles (51). Fatty acid vesicles have been shown to form in other putative early Earth environments, such as subaerial hot springs (52,53) and deep-sea hydrothermal vents (54); however, it is unclear whether any of these environments can also support the assembly of RNA, suggesting a possible unique role for soda lakes during the origin of life. ...
The origin of life likely occurred within environments that concentrated cellular precursors and enabled their co-assembly into cells. Soda lakes (those dominated by Na+ ions and carbonate species) can concentrate precursors of RNA and membranes, such as phosphate, cyanide, and fatty acids. Subsequent assembly of RNA and membranes into cells is a long-standing problem because RNA function requires divalent cations, e.g. Mg2+, but Mg2+ disrupts fatty acid membranes. The low solubility of Mg-containing carbonates limits soda lakes to moderate Mg2+ concentrations (∼1 mM), so we investigated whether both RNAs and membranes function within these lakes. We collected water from Last Chance Lake and Goodenough Lake in Canada. Because we sampled after seasonal evaporation, the lake water contained ∼1 M Na+ and ∼1 mM Mg2+ near pH 10. In the laboratory, nonenzymatic, RNA-templated polymerization of 2-aminoimidazole-activated ribonucleotides occurred at comparable rates in lake water and standard laboratory conditions (50 mM MgCl2, pH 8). Additionally, we found that a ligase ribozyme that uses oligonucleotide substrates activated with 2-aminoimidazole was active in lake water after adjusting pH from ∼10 to 9. We also observed that decanoic acid and decanol assembled into vesicles in a dilute solution that resembled lake water after seasonal rains, and that those vesicles retained encapsulated solutes despite salt-induced flocculation when the external solution was replaced with dry-season lake water. By identifying compatible conditions for nonenzymatic and ribozyme-catalyzed RNA assembly, and for encapsulation by membranes, our results suggest that soda lakes could have enabled cellular life to emerge on Earth, and perhaps elsewhere.
... Terrestrial geothermal pools are one of the prominent geological niches where life is thought to have originated. [40] Geothermal pool-like environments are known to facilitate prebiotically relevant events, including the assembly of singlechain amphiphiles into compartments, a process considered crucial for the emergence of the earliest protocells. [40] Therefore, we simulated these conditions using water samples collected from an astrobiological analogue geothermal pool located in Ladakh, India. ...
... [40] Geothermal pool-like environments are known to facilitate prebiotically relevant events, including the assembly of singlechain amphiphiles into compartments, a process considered crucial for the emergence of the earliest protocells. [40] Therefore, we simulated these conditions using water samples collected from an astrobiological analogue geothermal pool located in Ladakh, India. [41] In order to test the biophysical properties of the membrane systems, fluorescence-based studies were undertaken in the presence of various metal cations for both the homogenous oleic acid membrane system and the binary system of OA-GMO. ...
Spontaneous interactions between nucleotides and lipid membranes are likely to have played a prominent role in the emergence of life on Earth. However, the effect of nucleotides on the physicochemical properties of model protocellular membranes is relatively less understood. To this end, we aimed to discern the effect of canonical nucleotides on the properties of single‐chain amphiphile membranes under prebiotically relevant conditions of multiple wet‐dry cycles. Furthermore, the change in the critical aggregation concentration of the membranes and their stability in the presence of nucleotides was also investigated in astrobiologically relevant analogue environments. We report that different nucleotides, lipid headgroups, and the ionic makeup of the system affect lipid‐nucleotide interactions, and these, in turn, modulate the effect of nucleotides on the membrane properties. Specifically, the presence of AMP, UMP, and CMP promoted self‐assembly of oleic acid membranes and increased their stability against certain prebiotically relevant selection pressures. This study takes us a step towards an appreciable understanding of how nucleotides might have shaped the protocellular landscape of the prebiotic Earth.
... On the other hand, these lipophilic peptides could Hence, the prebiotic conditions tested here would have to be compatible with the presence of lipidic vesicles that might be invaded by such chimeric species. Indeed, some of the conditions previously reported would not be relevant in our scenario, since high concentrations of salts and divalent cations proved to be irreconcilable with the presence of most of the prebiotic lipidic vesicles [23,24]. First, random mixtures of (mainly) lipophilic peptides were generated from selected pools of prebiotic amino acids through activation with N,N'-carbonyldiimidazole (CDI) [25]. ...
... In addition, similar reaction conditions were tested in the absence of amino acids or peptides for the chemical ligation Hence, the prebiotic conditions tested here would have to be compatible with the presence of lipidic vesicles that might be invaded by such chimeric species. Indeed, some of the conditions previously reported would not be relevant in our scenario, since high concentrations of salts and divalent cations proved to be irreconcilable with the presence of most of the prebiotic lipidic vesicles [23,24]. First, random mixtures of (mainly) lipophilic peptides were generated from selected pools of prebiotic amino acids through activation with N,N'-carbonyldiimidazole (CDI) [25]. ...
... High concentrations of salts and divalent cations were bread-and-butter conditions for any condensation reaction involving oligonucleotides, since they favoured their hybridisation to complementary double strands needed for templated and primed strand elongation or ligation. However, these conditions would probably be fatal to most prebiotic lipid vesicles [23,24]. It seemed natural to presume that conditions similar to the ones used for the coupling attempts between peptides and oligonucleotides would be compatible with the presence of lipidic vesicles. ...
Deciphering the origins of life on a molecular level includes unravelling the numerous interactions that could occur between the most important biomolecules being the lipids, peptides and nucleotides. They were likely all present on the early Earth and all necessary for the emergence of cellular life. In this study, we intended to explore conditions that were at the same time conducive to chemical reactions critical for the origins of life (peptide–oligonucleotide couplings and templated ligation of oligonucleotides) and compatible with the presence of prebiotic lipid vesicles. For that, random peptides were generated from activated amino acids and analysed using NMR and MS, whereas short oligonucleotides were produced through solid-support synthesis, manually deprotected and purified using HPLC. After chemical activation in prebiotic conditions, the resulting mixtures were analysed using LC-MS. Vesicles could be produced through gentle hydration in similar conditions and observed using epifluorescence microscopy. Despite the absence of coupling or ligation, our results help to pave the way for future investigations on the origins of life that may gather all three types of biomolecules rather than studying them separately, as it is still too often the case.
... In addition to micelles, modern lipids can selfassemble into lamellar or non-lamellar lipid phases including liposomes, multi-lamellar vesicles, inverted micelles or hexagonal and cubic phases, which depends on factors such as chemical structure (e.g., whether the lipids have a conical or inverted triangular shape) and temperature, pressure, ionic strength and lipid concentration, among others [38][39][40]. For instance, a study [41] simulating the ability of fatty acids to form vesicles demonstrated that in aqueous solutions with low ionic strength, decanoic acid (C10:0) formed vesicular and multilamellar structures at pH 3.3 but formed semicrystalline structures at pH 7.9. Dodecanoic acid (C12:0) formed vesicles at both pH values, but formed crystals rather than vesicles in the presence of sea water [41]. ...
... For instance, a study [41] simulating the ability of fatty acids to form vesicles demonstrated that in aqueous solutions with low ionic strength, decanoic acid (C10:0) formed vesicular and multilamellar structures at pH 3.3 but formed semicrystalline structures at pH 7.9. Dodecanoic acid (C12:0) formed vesicles at both pH values, but formed crystals rather than vesicles in the presence of sea water [41]. Likewise, the ability of oleic acid (C18:1) to form micelles is highly dependent on starting concentration and temperature [40]. ...
The unique biophysical and biochemical properties of lipids render them crucial in most models of the origin of life (OoL). Many studies have attempted to delineate the prebiotic pathways by which lipids were formed, how micelles and vesicles were generated, and how these micelles and vesicles became selectively permeable towards the chemical precursors required to initiate and support biochemistry and inheritance. Our analysis of a number of such studies highlights the extremely narrow and limited range of conditions by which an experiment is considered to have successfully modeled a role for lipids in an OoL experiment. This is in line with a recent proposal that bias is introduced into OoL studies by the extent and the kind of human intervention. It is self-evident that OoL studies can only be performed by human intervention, and we now discuss the possibility that some assumptions and simplifications inherent in such experimental approaches do not permit determination of mechanistic insight into the roles of lipids in the OoL. With these limitations in mind, we suggest that more nuanced experimental approaches than those currently pursued may be required to elucidate the generation and function of lipids, micelles and vesicles in the OoL.
... The literature long suggested that fatty-acid vesicles could not form under oceanic hydrothermal conditions, but these results were mostly based on single (usually C 10 ) fatty acids or simple mixtures of only two or three amphiphiles (Maurer et al. 2018, Milshteyn et al. 2018, Monnard et al. 2002. Using more complex mixtures of six C 10 -C 15 fatty acids and six fatty alcohols or isoprenols, we have shown that mixed amphiphiles can readily self-assemble into vesicles with bilayer membranes under a wide range of conditions ( Jordan et al. 2019a,b). ...
The origin of life entails a continuum from simple prebiotic chemistry to cells with genes and molecular machines. Using life as a guide to this continuum, we consider how selection could promote increased complexity before the emergence of genes. Structured, far-from-equilibrium environments such as hydrothermal systems drive the reaction between CO 2 and H 2 to form organics that self-organize into protocells. CO 2 fixation within protocells generates a reaction network with a topology that prefigures the universal core of metabolism. Positive feedback loops amplify flux through this network, giving a metabolic heredity that promotes growth. Patterns in the genetic code show that genes and proteins arose through direct biophysical interactions between amino acids and nucleotides in this protometabolic network. Random genetic sequences template nonrandom peptides, producing selectable function in growing protocells. This context-dependent emergence of information gives rise seamlessly to an autotrophic last universal common ancestor.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 54 is November 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... While the sodium cation (11 g/L in SW) accounts for 31% of the weight of all ions in standard SW, the three cations studied in the present study (Mg 2+ , Ca 2+ and K + ; 2 g/L in SW) only account for a total of 6%. Only the chloride anion (Cl − ) was used because it is by far the most common in SW (19 g/L in SW): 55% of the weight of all ions, while the second most abundant anion (SO 2 − ; 3 g/L in SW) accounts for only 8% (e.g., Gilabert-Oriol et al., 2015;Milshteyn et al., 2018;Oren and Biesheuvel, 2018). Summarizing, three specific objectives were outlined in this study: 1) to assess the avoidance-selection behavior of D. rerio larvae, non-pre-exposed to lethal levels of salinity, when exposed to saline gradients created with different salts and SW in a non-confined system, 2) to assess the avoidance-selection behavior of D. rerio larvae, pre-exposed to lethal levels of salinity, under saline gradients created with different salts and SW in a non-confined system, 3) to compare the responses of non-pre-exposed and pre-exposed fish to understand if acclimation has a role in their selection relatively to the conductivity level, and 4) to compare the data obtained for SW with that reported in the literature for NaCl to if is the use of NaCl as a surrogate in SW intrusions frameworks is still protective if freshwater ecosystems. ...
The risk assessment of freshwater salinization is constructed around standard assays and using sodium chloride (NaCl), neglecting that the stressor is most likely a complex mixture of ions and the possibility of prior contact with it, triggering acclimation mechanisms in the freshwater biota. To date, as far as we are aware of, no information has been generated integrating both acclimation and avoidance behavior that may allow these risk assessments upgrading. Accordingly, 6-days-old Danio rerio larvae were selected to perform 12-h avoidance assays in a non-confined 6-compartment linear system to simulate conductivity gradients using seawater (SW) and the chloride salts MgCl2, KCl, and CaCl2. Salinity gradients were established from conductivities known to cause 50% egg mortality in a 96-h exposure (LC50,96h,embryo). The triggering of acclimation processes, which could influence organisms' avoidance-selection under the conductivity gradients, was also studied using larvae pre-exposed to lethal levels of each salt or SW. Median avoidance conductivities after a 12-h of exposure (AC50,12h), and the Population Immediate Decline (PID) were computed. All non-pre-exposed larvae were able to detect and flee from conductivities corresponding to the LC50,96h,embryo, selecting compartments with lower conductivities, except for KCl. The AC50,12h and LC50,96h overlapped for MgCl2 and CaCl2, though the former is considered as more sensitive as it was obtained in 12 h of exposure. The AC50,12h for SW was 1.83-fold lower than the LC50,96h, thus, reinforcing the higher sensitivity of the parameter ACx and its adequacy for risk assessment frameworks. The PID, at low conductivities, was solely explained by the avoidance behavior of non-pre-exposed larvae. Larvae pre-exposed to lethal levels of salt or SW were found to select higher conductivities, except for MgCl2. Results indicated that avoidance-selection assays are ecologically relevant and sensitive tools to be used in risk assessment processes. Stressor pre-exposure influenced organisms' avoidance-selection behavior under conductivity gradients, suggesting that under salinization events organisms may acclimate, remaining in altered habitats.
... The synthesized amino acids would likely be polymerized via condensation reactions forming peptides [80]. It is worth mentioning that if carboxylic acids are deposited on mineral surfaces, they can form dried reactive films which then assemble into membranous vesicles [81]. ...
Life most likely started during the Hadean Eon; however, the environmental conditions which contributed to the complexity of its chemistry are poorly known. A better understanding of various environmental conditions, including global (heliospheric) and local (atmospheric, surface, and oceanic), along with the internal dynamic conditions of the early Earth, are required to understand the onset of abiogenesis. Herein, we examine the contributions of galactic cosmic rays (GCRs) and solar energetic particles (SEPs) associated with superflares from the young Sun to the formation of amino acids and carboxylic acids in weakly reduced gas mixtures representing the early Earth’s atmosphere. We also compare the products with those introduced by lightning events and solar ultraviolet light (UV). In a series of laboratory experiments, we detected and characterized the formation of amino acids and carboxylic acids via proton irradiation of a mixture of carbon dioxide, methane, nitrogen, and water in various mixing ratios. These experiments show the detection of amino acids after acid hydrolysis when 0.5% (v/v) of initial methane was introduced to the gas mixture. In the set of experiments with spark discharges (simulation of lightning flashes) performed for the same gas mixture, we found that at least 15% methane was required to detect the formation of amino acids, and no amino acids were detected in experiments via UV irradiation, even when 50% methane was used. Carboxylic acids were formed in non-reducing gas mixtures (0% methane) by proton irradiation and spark discharges. Hence, we suggest that GCRs and SEP events from the young Sun represent the most effective energy sources for the prebiotic formation of biologically important organic compounds from weakly reducing atmospheres. Since the energy flux of space weather, which generated frequent SEPs from the young Sun in the first 600 million years after the birth of the solar system, was expected to be much greater than that of GCRs, we conclude that SEP-driven energetic protons are the most promising energy sources for the prebiotic production of bioorganic compounds in the atmosphere of the Hadean Earth.
... The problems associated with fatty acids vesicle formation and stability are; (1) the narrow range of alkaline pH in which vesicles spontaneously form [42], (2) salt flocculation (agglomeration at high salt concentrations) [43,44], and (3) high critical vesiculation concentration (critical concentration of fatty acids required for spontaneous vesicle formation), higher than, for example, the equivalent for phospholipid vesicle formation [1,45]. ...
Theories on life’s origin generally acknowledge the advantage of a semi-permeable vesicle (protocell) for enhancing the chemical reaction–diffusion processes involved in abiogenesis. However, more and more evidence indicates that the origin of life is concerned with the photo-chemical dissipative structuring of the fundamental molecules under soft UV-C light (245–275 nm). In this paper, we analyze the Mie UV scattering properties of such a vesicle created with long-chain fatty acids. We find that the vesicle could have provided early life with a shield from the faint but destructive hard UV-C ionizing light (180–210 nm) that probably bathed Earth’s surface from before the origin of life and at least until 1200 million years after, until the formation of a protective ozone layer as a result of the evolution of oxygenic photosynthesis.
