Special Issue "Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms"

A special issue of Life (ISSN 2075-1729).

Deadline for manuscript submissions: closed (15 September 2017)

Special Issue Editors

Guest Editor
Prof. Kunio Kawamura

Hiroshima Shudo University, Department of Human Environmental Studies Ozuka higashi 1-1-1, Asaminami-ku, Hiroshima, ZIP 731-3195, Japan
Website | E-Mail
Interests: analytical chemistry; nucleic acid chemistry; origin of life; environmental science; theory of origin and evolution of biospheres
Co-Guest Editor
Dr. Norio Kitadai

Earth-Life science institute, Toyko institute of technology,Toyko, 152-8550, Japan
Website | E-Mail
Interests: astrobiology; Carbon fixation; chemical evolution; deep-sea hydrothermal systems; electrochemistry; Hadean; origin of life

Special Issue Information

Dear Colleagues,

Hydrothermal reaction systems, such as submarine hydrothermal vent systems, are considered as key environments, where different type of chemical evolution processes could have carried out to form primitive life-like systems. Here, we would like to refocus how such hydrothermal environments could have contributed the formation of life in order to deduce the feature of ancient life forms.

The accumulation of biomolecules was an essential step for chemical evolution under the extreme Earth environments. Several types of simulation experiments of hydrothermal environments on the primitive Earth, and kinetics and thermodynamic analyses on the behavior of biomolecules have been carried out in relation to the prebiotic formation and stability of biomolecules, such as RNA and peptides. Naturally, instrumentation for simulation of the hydrothermal environments is a key approach for the successful studies on the chemical evolution of biomolecules. Diversity of hydrothermal environments, such as oscillating systems, is now becoming important even from the astrobiological viewpoint. Hydrothermal systems could be widely present in different planets other than the Earth and moons in the Solar system.

Although biomolecules and organisms were considered in a long time to resist unlikely the hydrothermal environments, the discoveries of thermophilic organisms and phylogenetic analyses have implied the hypothesis that life-like systems could have emerged under the relatively high temperature conditions. Simulation experiments of biomolecules under hydrothermal conditions support that this is a narrow view. At the same time, the hydrothermal environments are carefully verified since it does not seem to be plausible for the accumulation and chemical evolution of biomolecules, such as RNA and peptides.

According to these reasons, the hydrothermal systems are considered as key environments for the mergence of life-like systems. In this Special Issue, the roles and importance of hydrothermal systems will be refocused from various viewpoints.

Prof. Kunio Kawamura
Guest Editor

Manuscript Submission Information

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Keywords

  • Hydrothermal environments
  • RNA world
  • Biomolecules
  • Instrumentation
  • Prebiotic
  • Astrobiology
  • Hadean

Published Papers (7 papers)

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Research

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Open AccessArticle Amphiphilic Compounds Assemble into Membranous Vesicles in Hydrothermal Hot Spring Water but Not in Seawater
Received: 12 March 2018 / Revised: 28 April 2018 / Accepted: 2 May 2018 / Published: 10 May 2018
Cited by 2 | PDF Full-text (5358 KB) | HTML Full-text | XML Full-text
Abstract
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 [...] Read more.
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 simple amphiphilic compounds are in terms of their ability to assemble into stable vesicles, we chose to study 10- and 12-carbon monocarboxylic acids and a mixture of the latter with its monoglyceride. These were dispersed in hydrothermal water samples drawn directly from hot springs in Yellowstone National Park at two pH ranges, and the results were compared with sea water under the same conditions. We found that the pure acids could form membranous vesicles in hydrothermal pool water, but that a mixture of dodecanoic acid and glycerol monododecanoate was less temperature-sensitive and assembled into relatively stable membranes at both acidic and alkaline pH ranges. Furthermore, the vesicles were able to encapsulate nucleic acids and pyranine, a fluorescent anionic dye. None of the amphiphiles that were tested formed stable vesicles in sea water because the high ionic concentrations disrupted membrane stability. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Open AccessArticle Formation and Stability of Prebiotically Relevant Vesicular Systems in Terrestrial Geothermal Environments
Received: 21 October 2017 / Revised: 23 November 2017 / Accepted: 28 November 2017 / Published: 30 November 2017
Cited by 3 | PDF Full-text (2519 KB) | HTML Full-text | XML Full-text | Supplementary Files
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Review

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Open AccessReview The Impact of Salts on Single Chain Amphiphile Membranes and Implications for the Location of the Origin of Life
Received: 19 September 2017 / Revised: 6 November 2017 / Accepted: 7 November 2017 / Published: 14 November 2017
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Abstract
One of the key steps in the origins of life was the formation of a membrane to separate protocells from their environment. These membranes are proposed to have been formed out of single chain amphiphiles, which are less stable than the dialkyl lipids [...] Read more.
One of the key steps in the origins of life was the formation of a membrane to separate protocells from their environment. These membranes are proposed to have been formed out of single chain amphiphiles, which are less stable than the dialkyl lipids used to form modern membranes. This lack of stability, specifically for decanoate, is often used to refute ocean locations for the origins of life. This review addresses the formation of membranes in hydrothermal-vent like conditions, as well as other environmental constraints. Specifically, single chain amphiphiles can form membranes at high sea salt concentrations (150 g/L), high temperatures (65 °C), and a wide pH range (2 to 10). It additionally discusses the major challenges and advantages of membrane formation in both ocean and fresh water locations. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Open AccessReview Hydrothermal Microflow Technology as a Research Tool for Origin-of-Life Studies in Extreme Earth Environments
Received: 31 August 2017 / Revised: 25 September 2017 / Accepted: 30 September 2017 / Published: 2 October 2017
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Abstract
Although studies about the origin of life are a frontier in science and a number of effective approaches have been developed, drawbacks still exist. Examples include: (1) simulation of chemical evolution experiments (which were demonstrated for the first time by Stanley Miller); (2) [...] Read more.
Although studies about the origin of life are a frontier in science and a number of effective approaches have been developed, drawbacks still exist. Examples include: (1) simulation of chemical evolution experiments (which were demonstrated for the first time by Stanley Miller); (2) approaches tracing back the most primitive life-like systems (on the basis of investigations of present organisms); and (3) constructive approaches for making life-like systems (on the basis of molecular biology), such as in vitro construction of the RNA world. Naturally, simulation experiments of chemical evolution under plausible ancient Earth environments have been recognized as a potentially fruitful approach. Nevertheless, simulation experiments seem not to be sufficient for identifying the scenario from molecules to life. This is because primitive Earth environments are still not clearly defined and a number of possibilities should be taken into account. In addition, such environments frequently comprise extreme conditions when compared to the environments of present organisms. Therefore, we need to realize the importance of accurate and convenient experimental approaches that use practical research tools, which are resistant to high temperature and pressure, to facilitate chemical evolution studies. This review summarizes improvements made in such experimental approaches over the last two decades, focusing primarily on our hydrothermal microflow reactor technology. Microflow reactor systems are a powerful tool for performing simulation experiments in diverse simulated hydrothermal Earth conditions in order to measure the kinetics of formation and degradation and the interactions of biopolymers. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Open AccessReview Ancient Living Organisms Escaping from, or Imprisoned in, the Vents?
Received: 25 August 2017 / Revised: 11 September 2017 / Accepted: 11 September 2017 / Published: 15 September 2017
Cited by 1 | PDF Full-text (1042 KB) | HTML Full-text | XML Full-text
Abstract
We have recently criticised the natural pH gradient hypothesis which purports to explain how the difference in pH between fluid issuing from ancient alkali vents and the more acidic Hadean ocean could have driven molecular machines that catalyse reactions that are useful in [...] Read more.
We have recently criticised the natural pH gradient hypothesis which purports to explain how the difference in pH between fluid issuing from ancient alkali vents and the more acidic Hadean ocean could have driven molecular machines that catalyse reactions that are useful in prebiotic and autotrophic chemistry. In this article, we temporarily suspend our earlier criticism while we consider difficulties for primitive organisms to have managed their energy supply and to have left the vents and become free-living. We point out that it may have been impossible for organisms to have acquired membrane-located proton (or sodium ion) pumps to replace the natural pH gradient, and independently to have driven essential molecular machines such as the ATP synthase. The volumes of the ocean and of the vent fluids were too large for a membrane-located pump to have generated a significant ion concentration gradient. Our arguments apply to three of the four concurrent models employed by the proponents of the natural pH gradient hypothesis. A fourth model is exempt from these arguments but has other intrinsic difficulties that we briefly consider. We conclude that ancient organisms utilising a natural pH gradient would have been imprisoned in the vents, unable to escape and become free-living. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Open AccessReview Characterization of Reconstructed Ancestral Proteins Suggests a Change in Temperature of the Ancient Biosphere
Received: 19 July 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 6 August 2017
Cited by 4 | PDF Full-text (1428 KB) | HTML Full-text | XML Full-text
Abstract
Understanding the evolution of ancestral life, and especially the ability of some organisms to flourish in the variable environments experienced in Earth’s early biosphere, requires knowledge of the characteristics and the environment of these ancestral organisms. Information about early life and environmental conditions [...] Read more.
Understanding the evolution of ancestral life, and especially the ability of some organisms to flourish in the variable environments experienced in Earth’s early biosphere, requires knowledge of the characteristics and the environment of these ancestral organisms. Information about early life and environmental conditions has been obtained from fossil records and geological surveys. Recent advances in phylogenetic analysis, and an increasing number of protein sequences available in public databases, have made it possible to infer ancestral protein sequences possessed by ancient organisms. However, the in silico studies that assess the ancestral base content of ribosomal RNAs, the frequency of each amino acid in ancestral proteins, and estimate the environmental temperatures of ancient organisms, show conflicting results. The characterization of ancestral proteins reconstructed in vitro suggests that ancient organisms had very thermally stable proteins, and therefore were thermophilic or hyperthermophilic. Experimental data supports the idea that only thermophilic ancestors survived the catastrophic increase in temperature of the biosphere that was likely associated with meteorite impacts during the early history of Earth. In addition, by expanding the timescale and including more ancestral proteins for reconstruction, it appears as though the Earth’s surface temperature gradually decreased over time, from Archean to present. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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Other

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Open AccessPerspective Origin of the Reductive Tricarboxylic Acid (rTCA) Cycle-Type CO2 Fixation: A Perspective
Received: 15 September 2017 / Revised: 10 October 2017 / Accepted: 17 October 2017 / Published: 23 October 2017
Cited by 2 | PDF Full-text (1307 KB) | HTML Full-text | XML Full-text
Abstract
The reductive tricarboxylic acid (rTCA) cycle is among the most plausible candidates for the first autotrophic metabolism in the earliest life. Extant enzymes fixing CO2 in this cycle contain cofactors at the catalytic centers, but it is unlikely that the protein/cofactor system [...] Read more.
The reductive tricarboxylic acid (rTCA) cycle is among the most plausible candidates for the first autotrophic metabolism in the earliest life. Extant enzymes fixing CO2 in this cycle contain cofactors at the catalytic centers, but it is unlikely that the protein/cofactor system emerged at once in a prebiotic process. Here, we discuss the feasibility of non-enzymatic cofactor-assisted drive of the rTCA reactions in the primitive Earth environments, particularly focusing on the acetyl-CoA conversion to pyruvate. Based on the energetic and mechanistic aspects of this reaction, we propose that the deep-sea hydrothermal vent environments with active electricity generation in the presence of various sulfide catalysts are a promising setting for it to progress. Our view supports the theory of an autotrophic origin of life from primordial carbon assimilation within a sulfide-rich hydrothermal vent. Full article
(This article belongs to the Special Issue Hydrothermal Vents or Hydrothermal Fields: Challenging Paradigms)
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