Formation and Stability of Prebiotically Relevant Vesicular Systems in Terrestrial Geothermal Environments

Abstract

Terrestrial geothermal fields and oceanic hydrothermal vents are considered as candidate environments for the emergence of life on Earth. Nevertheless, the ionic strength and salinity of oceans present serious limitations for the self-assembly of amphiphiles, a process that is fundamental for the formation of first protocells. Consequently, we systematically characterized the efficiency of amphiphile assembly, and vesicular stability, in terrestrial geothermal environments, both, under simulated laboratory conditions and in hot spring water samples (collected from Ladakh, India, an Astrobiologically relevant site). Combinations of prebiotically pertinent fatty acids and their derivatives were evaluated for the formation of vesicles in aforesaid scenarios. Additionally, the stability of these vesicles was characterized over multiple dehydration-rehydration cycles, at elevated temperatures. Among the combinations that were tested, mixtures of fatty acid and its glycerol derivatives were found to be the most robust, also resulting in vesicles in all of the hot spring waters that were tested. Importantly, these vesicles were stable at high temperatures, and this fatty acid system retained its vesicle forming propensity, even after multiple cycles of dehydration-rehydration. The remaining systems, however, formed vesicles only in bicine buffer. Our results suggest that certain prebiotic compartments would have had a selective advantage in terrestrial geothermal niches. Significantly, our study highlights the importance of validating results that are obtained under ‘buffered’ laboratory conditions, by verifying their plausibility in prebiotically analogous environments.

Amphiphilic Compounds Assemble into Membranous Vesicles in Hydrothermal Hot Spring Water but Not in Seawater

“…The main conclusions from the results reported here is that, although pure decanoic and dodecanoic acid are able to form membranous vesicles in hydrothermal water samples from hydrothermal pools, they are relatively sensitive to temperature and pH. Similar results have been reported for self-assembly of amphiphilic fatty acid in an Indian geothermal environment [ 13 ]. In contrast, a mixture of a fatty acid and its monoglyceride (LA–GML) assembles into stable membranous vesicles in hot spring water at alkaline and acidic pH ranges and is less sensitive to pH.…”

“…Lipid vesicles prepared in these conditions are usually composed of phospholipids, such as phosphatidylcholine, but it is implausible that phospholipids would be available in the prebiotic conditions because their synthesis today depends on metabolism. Amphiphiles, such as fatty acids and their monoglycerides, are more plausible choices, but the pH and ionic composition of an aqueous phase strongly affects the ability of amphiphilic compounds to assemble into membranes [ 9 , 10 , 11 , 12 , 13 ].…”

Geochemical influences on nonenzymatic oligomerization of prebiotically relevant cyclic nucleotides

“…Nonetheless, high amounts of salt is known to be detrimental for RNA (Blasko and Bruice 1999). Panamic hot spring water from Joshi et al study was chosen, to study the afore-mentioned oligomerization reactions (Joshi et al 2017) in detail. This site was studied as part of Spaceward Bound expedition to Ladakh, an astrobiologically relevant site in the northern part of India (Pandey et al 2019).…”

“…tried to constrain the range of possible environments/conditions for the origins of life by analyzing prebiotically pertinent prebiotic processes under realistic conditions (Deamer et al 2006). Previous study in our lab have Dagar, S. 6 demonstrated the self-assembly of simple amphiphiles, like fatty acids and their derivatives, in alkaline hot spring water samples of varying ionic content that were collected from three locations in Ladakh, an early Earth analogue site (Joshi et al 2017). However, to our knowledge, similar analogue environment studies have not been undertaken in the context of nonenzymatic oligomerization of nucleotides to form RNA.…”

“…However, to our knowledge, similar analogue environment studies have not been undertaken in the context of nonenzymatic oligomerization of nucleotides to form RNA. Therefore, we also set out to investigate how cyclic nucleotide oligomerization reactions would advent if the reactions were to be carried out in a complex 'realistic' context, instead of a controlled laboratory set-up by using the same hot spring sample that were used in the previous study (Joshi et al 2017).…”