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Life, Volume 4, Issue 3 (September 2014), Pages 281-534

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Research

Jump to: Review

Open AccessArticle Prebiotic RNA Synthesis by Montmorillonite Catalysis
Life 2014, 4(3), 318-330; doi:10.3390/life4030318
Received: 24 December 2013 / Revised: 29 June 2014 / Accepted: 4 July 2014 / Published: 5 August 2014
Cited by 2 | PDF Full-text (813 KB) | HTML Full-text | XML Full-text
Abstract
This review summarizes our recent findings on the role of mineral salts in prebiotic RNA synthesis, which is catalyzed by montmorillonite clay minerals. The clay minerals not only catalyze the synthesis of RNA but also facilitate homochiral selection. Preliminary data of these [...] Read more.
This review summarizes our recent findings on the role of mineral salts in prebiotic RNA synthesis, which is catalyzed by montmorillonite clay minerals. The clay minerals not only catalyze the synthesis of RNA but also facilitate homochiral selection. Preliminary data of these findings have been presented at the “Horizontal Gene Transfer and the Last Universal Common Ancestor (LUCA)” conference at the Open University, Milton Keynes, UK, 5–6 September 2013. The objective of this meeting was to recognize the significance of RNA in LUCA. We believe that the prebiotic RNA synthesis from its monomers must have been a simple process. As a first step, it may have required activation of the 5'-end of the mononucleotide with a leaving group, e.g., imidazole in our model reaction (Figure 1). Wide ranges of activating groups are produced from HCN under plausible prebiotic Earth conditions. The final step is clay mineral catalysis in the presence of mineral salts to facilitate selective production of functional RNA. Both the clay minerals and mineral salts would have been abundant on early Earth. We have demonstrated that while montmorillonite (pH 7) produced only dimers from its monomers in water, addition of sodium chloride (1 M) enhanced the chain length multifold, as detected by HPLC. The effect of monovalent cations on RNA synthesis was of the following order: Li+ > Na+ > K+. A similar effect was observed with the anions, enhancing catalysis in the following order: Cl > Br > I. The montmorillonite-catalyzed RNA synthesis was not affected by hydrophobic or hydrophilic interactions. We thus show that prebiotic synthesis of RNA from its monomers was a simple process requiring only clay minerals and a small amount of salt. Full article
(This article belongs to the Special Issue Horizontal Gene Transfer and the Last Universal Common Ancestor)
Open AccessCommunication Supercritical Carbon Dioxide and Its Potential as a Life-Sustaining Solvent in a Planetary Environment
Life 2014, 4(3), 331-340; doi:10.3390/life4030331
Received: 25 June 2014 / Revised: 30 July 2014 / Accepted: 31 July 2014 / Published: 8 August 2014
Cited by 11 | PDF Full-text (903 KB) | HTML Full-text | XML Full-text
Abstract
Supercritical fluids have different properties compared to regular fluids and could play a role as life-sustaining solvents on other worlds. Even on Earth, some bacterial species have been shown to be tolerant to supercritical fluids. The special properties of supercritical fluids, which [...] Read more.
Supercritical fluids have different properties compared to regular fluids and could play a role as life-sustaining solvents on other worlds. Even on Earth, some bacterial species have been shown to be tolerant to supercritical fluids. The special properties of supercritical fluids, which include various types of selectivities (e.g., stereo-, regio-, and chemo-selectivity) have recently been recognized in biotechnology and used to catalyze reactions that do not occur in water. One suitable example is enzymes when they are exposed to supercritical fluids such as supercritical carbon dioxide: enzymes become even more stable, because they are conformationally rigid in the dehydrated state. Furthermore, enzymes in anhydrous organic solvents exhibit a “molecular memory”, i.e., the capacity to “remember” a conformational or pH state from being exposed to a previous solvent. Planetary environments with supercritical fluids, particularly supercritical carbon dioxide, exist, even on Earth (below the ocean floor), on Venus, and likely on Super-Earth type exoplanets. These planetary environments may present a possible habitat for exotic life. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Figures

Open AccessArticle Three-Dimensional Algebraic Models of the tRNA Code and 12 Graphs for Representing the Amino Acids
Life 2014, 4(3), 341-373; doi:10.3390/life4030341
Received: 29 April 2014 / Revised: 23 July 2014 / Accepted: 25 July 2014 / Published: 11 August 2014
Cited by 3 | PDF Full-text (1572 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Three-dimensional algebraic models, also called Genetic Hotels, are developed to represent the Standard Genetic Code, the Standard tRNA Code (S-tRNA-C), and the Human tRNA code (H-tRNA-C). New algebraic concepts are introduced to be able to describe these models, to wit, the generalization [...] Read more.
Three-dimensional algebraic models, also called Genetic Hotels, are developed to represent the Standard Genetic Code, the Standard tRNA Code (S-tRNA-C), and the Human tRNA code (H-tRNA-C). New algebraic concepts are introduced to be able to describe these models, to wit, the generalization of the 2n-Klein Group and the concept of a subgroup coset with a tail. We found that the H-tRNA-C displayed broken symmetries in regard to the S-tRNA-C, which is highly symmetric. We also show that there are only 12 ways to represent each of the corresponding phenotypic graphs of amino acids. The averages of statistical centrality measures of the 12 graphs for each of the three codes are carried out and they are statistically compared. The phenotypic graphs of the S-tRNA-C display a common triangular prism of amino acids in 10 out of the 12 graphs, whilst the corresponding graphs for the H-tRNA-C display only two triangular prisms. The graphs exhibit disjoint clusters of amino acids when their polar requirement values are used. We contend that the S-tRNA-C is in a frozen-like state, whereas the H-tRNA-C may be in an evolving state. Full article
(This article belongs to the Special Issue The Origins and Early Evolution of RNA)
Figures

Open AccessCommunication Fluorine-Rich Planetary Environments as Possible Habitats for Life
Life 2014, 4(3), 374-385; doi:10.3390/life4030374
Received: 7 July 2014 / Revised: 4 August 2014 / Accepted: 5 August 2014 / Published: 18 August 2014
Cited by 2 | PDF Full-text (1655 KB) | HTML Full-text | XML Full-text
Abstract
In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we [...] Read more.
In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we know it. Biomolecules, when fluorinated such as peptides or proteins, exhibit a “fluorous effect”, i.e., they are fluorophilic (neither hydrophilic nor lipophilic). Such polymers, capable of creating self-sorting assemblies, resist denaturation by organic solvents by exclusion of fluorocarbon side chains from the organic phase. Fluorous cores consist of a compact interior, which is shielded from the surrounding solvent. Thus, we can anticipate that fluorine-containing “teflon”-like or “non-sticking” building blocks might be monomers of choice for the synthesis of organized polymeric structures in fluorine-rich planetary environments. Although no fluorine-rich planetary environment is known, theoretical considerations might help us to define chemistries that might support life in such environments. For example, one scenario is that all molecular oxygen may be used up by oxidation reactions on a planetary surface and fluorine gas could be released from F-rich magma later in the history of a planetary body to result in a fluorine-rich planetary environment. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
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Open AccessArticle Models of Formation and Activity of Spring Mounds in the Mechertate-Chrita-Sidi El Hani System, Eastern Tunisia: Implications for the Habitability of Mars
Life 2014, 4(3), 386-432; doi:10.3390/life4030386
Received: 31 May 2014 / Revised: 25 July 2014 / Accepted: 28 July 2014 / Published: 28 August 2014
Cited by 1 | PDF Full-text (14286 KB) | HTML Full-text | XML Full-text
Abstract
Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we [...] Read more.
Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we investigate models of formation and activity of well-exposed spring mounds in the Mechertate-Chrita-Sidi El Hani (MCSH) system, eastern Tunisia. We then use these models to explore possible spring mound formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. As they are oriented preferentially along faults, they can be considered as fault spring mounds, implying a tectonic influence in their formation process. However, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system also allows consideration of an origin as artesian spring mounds. In the case of the MCSH system, our geologic data presented here show that both models are valid, and we propose a combined hydro-tectonic model as the likely formation mechanism of artesian-fault spring mounds. During their evolution from the embryonic (early) to the islet (“island”) stages, spring mounds are also shaped by eolian accumulations and induration processes. Similarly, spring mounds have been suggested to be relatively common in certain provinces on the Martian surface, but their mode of formation is still a matter of debate. We propose that the tectonic, hydraulic, and combined hydro-tectonic models describing the spring mounds at MCSH could be relevant as Martian analogs because: (i) the Martian subsurface may be over pressured, potentially expelling mineral-enriched waters as spring mounds on the surface; (ii) the Martian subsurface may be fractured, causing alignment of the spring mounds in preferential orientations; and (iii) indurated eolian sedimentation and erosional remnants are common features on Mars. The spring mounds further bear diagnostic mineralogic and magnetic properties, in comparison with their immediate surroundings. Consequently, remote sensing techniques can be very useful to identify similar spring mounds on Mars. The mechanisms (tectonic and/or hydraulic) of formation and evolution of spring mounds at the MCSH system are suitable for the proliferation and protection of life respectively. Similarly, life or its resulting biomarkers on Mars may have been protected or preserved under the spring mounds. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessArticle A Model of Filamentous Cyanobacteria Leading to Reticulate Pattern Formation
Life 2014, 4(3), 433-456; doi:10.3390/life4030433
Received: 2 June 2014 / Revised: 9 August 2014 / Accepted: 14 August 2014 / Published: 3 September 2014
Cited by 4 | PDF Full-text (17549 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The filamentous cyanobacterium, Pseudanabaena, has been shown to produce reticulate patterns that are thought to be the result of its gliding motility. Similar fossilized structures found in the geological record constitute some of the earliest signs of life on Earth. It is [...] Read more.
The filamentous cyanobacterium, Pseudanabaena, has been shown to produce reticulate patterns that are thought to be the result of its gliding motility. Similar fossilized structures found in the geological record constitute some of the earliest signs of life on Earth. It is difficult to tie these fossils, which are billions of years old, directly to the specific microorganisms that built them. Identifying the physicochemical conditions and microorganism properties that lead microbial mats to form macroscopic structures can lead to a better understanding of the conditions on Earth at the dawn of life. In this article, a cell-based model is used to simulate the formation of reticulate patterns in cultures of Pseudanabaena. A minimal system of long and flexible trichomes capable of gliding motility is shown to be sufficient to produce stable patterns consisting of a network of streams. Varying model parameters indicate that systems with little to no cohesion, high trichome density and persistent movement are conducive to reticulate pattern formation, in conformance with experimental observations. Full article
(This article belongs to the Special Issue Cyanobacteria: Ecology, Physiology and Genetics)
Open AccessArticle Designing with Protocells: Applications of a Novel Technical Platform
Life 2014, 4(3), 457-490; doi:10.3390/life4030457
Received: 2 August 2014 / Accepted: 25 August 2014 / Published: 5 September 2014
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Abstract
The paper offers a design perspective on protocell applications and presents original research that characterizes the life-like qualities of the Bütschli dynamic droplet system, as a particular “species” of protocell. Specific focus is given to the possibility of protocell species becoming a [...] Read more.
The paper offers a design perspective on protocell applications and presents original research that characterizes the life-like qualities of the Bütschli dynamic droplet system, as a particular “species” of protocell. Specific focus is given to the possibility of protocell species becoming a technical platform for designing and engineering life-like solutions to address design challenges. An alternative framing of the protocell, based on process philosophy, sheds light on its capabilities as a technology that can deal with probability and whose ontology is consistent with complexity, nonlinear dynamics and the flow of energy and matter. However, the proposed technical systems do not yet formally exist as products or mature technologies. Their potential applications are therefore experimentally examined within a design context as architectural “projects”—an established way of considering proposals that have not yet been realized, like an extended hypothesis. Exemplary design-led projects are introduced, such as The Hylozoic Ground and Future Venice, which aim to “discover”, rather than “solve”, challenges to examine a set of possibilities that have not yet been resolved. The value of such exploration in design practice is in opening up a set of potential directions for further assessment before complex challenges are procedurally implemented. Full article
(This article belongs to the Special Issue Protocells - Designs for Life)

Review

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Open AccessReview Cognitive Neuroscience in Space
Life 2014, 4(3), 281-294; doi:10.3390/life4030281
Received: 19 March 2014 / Revised: 11 June 2014 / Accepted: 23 June 2014 / Published: 3 July 2014
Cited by 3 | PDF Full-text (917 KB) | HTML Full-text | XML Full-text
Abstract
Humans are the most adaptable species on this planet, able to live in vastly different environments on Earth. Space represents the ultimate frontier and a true challenge to human adaptive capabilities. As a group, astronauts and cosmonauts are selected for their ability [...] Read more.
Humans are the most adaptable species on this planet, able to live in vastly different environments on Earth. Space represents the ultimate frontier and a true challenge to human adaptive capabilities. As a group, astronauts and cosmonauts are selected for their ability to work in the highly perilous environment of space, giving their best. Terrestrial research has shown that human cognitive and perceptual motor performances deteriorate under stress. We would expect to observe these effects in space, which currently represents an exceptionally stressful environment for humans. Understanding the neurocognitive and neuropsychological parameters influencing space flight is of high relevance to neuroscientists, as well as psychologists. Many of the environmental characteristics specific to space missions, some of which are also present in space flight simulations, may affect neurocognitive performance. Previous work in space has shown that various psychomotor functions degrade during space flight, including central postural functions, the speed and accuracy of aimed movements, internal timekeeping, attentional processes, sensing of limb position and the central management of concurrent tasks. Other factors that might affect neurocognitive performance in space are illness, injury, toxic exposure, decompression accidents, medication side effects and excessive exposure to radiation. Different tools have been developed to assess and counteract these deficits and problems, including computerized tests and physical exercise devices. It is yet unknown how the brain will adapt to long-term space travel to the asteroids, Mars and beyond. This work represents a comprehensive review of the current knowledge and future challenges of cognitive neuroscience in space from simulations and analog missions to low Earth orbit and beyond. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessReview Protein and Essential Amino Acids to Protect Musculoskeletal Health during Spaceflight: Evidence of a Paradox?
Life 2014, 4(3), 295-317; doi:10.3390/life4030295
Received: 13 March 2014 / Revised: 19 June 2014 / Accepted: 23 June 2014 / Published: 11 July 2014
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Abstract
Long-duration spaceflight results in muscle atrophy and a loss of bone mineral density. In skeletal muscle tissue, acute exercise and protein (e.g., essential amino acids) stimulate anabolic pathways (e.g., muscle protein synthesis) both independently and synergistically to maintain neutral or positive net [...] Read more.
Long-duration spaceflight results in muscle atrophy and a loss of bone mineral density. In skeletal muscle tissue, acute exercise and protein (e.g., essential amino acids) stimulate anabolic pathways (e.g., muscle protein synthesis) both independently and synergistically to maintain neutral or positive net muscle protein balance. Protein intake in space is recommended to be 12%–15% of total energy intake (≤1.4 g∙kg1∙day1) and spaceflight is associated with reduced energy intake (~20%), which enhances muscle catabolism. Increasing protein intake to 1.5–2.0 g∙kg1∙day1 may be beneficial for skeletal muscle tissue and could be accomplished with essential amino acid supplementation. However, increased consumption of sulfur-containing amino acids is associated with increased bone resorption, which creates a dilemma for musculoskeletal countermeasures, whereby optimizing skeletal muscle parameters via essential amino acid supplementation may worsen bone outcomes. To protect both muscle and bone health, future unloading studies should evaluate increased protein intake via non-sulfur containing essential amino acids or leucine in combination with exercise countermeasures and the concomitant influence of reduced energy intake. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessReview Space Radiation: The Number One Risk to Astronaut Health beyond Low Earth Orbit
Life 2014, 4(3), 491-510; doi:10.3390/life4030491
Received: 10 June 2014 / Revised: 6 August 2014 / Accepted: 21 August 2014 / Published: 11 September 2014
Cited by 8 | PDF Full-text (4014 KB) | HTML Full-text | XML Full-text
Abstract
Projecting a vision for space radiobiological research necessitates understanding the nature of the space radiation environment and how radiation risks influence mission planning, timelines and operational decisions. Exposure to space radiation increases the risks of astronauts developing cancer, experiencing central nervous system [...] Read more.
Projecting a vision for space radiobiological research necessitates understanding the nature of the space radiation environment and how radiation risks influence mission planning, timelines and operational decisions. Exposure to space radiation increases the risks of astronauts developing cancer, experiencing central nervous system (CNS) decrements, exhibiting degenerative tissue effects or developing acute radiation syndrome. One or more of these deleterious health effects could develop during future multi-year space exploration missions beyond low Earth orbit (LEO). Shielding is an effective countermeasure against solar particle events (SPEs), but is ineffective in protecting crew members from the biological impacts of fast moving, highly-charged galactic cosmic radiation (GCR) nuclei. Astronauts traveling on a protracted voyage to Mars may be exposed to SPE radiation events, overlaid on a more predictable flux of GCR. Therefore, ground-based research studies employing model organisms seeking to accurately mimic the biological effects of the space radiation environment must concatenate exposures to both proton and heavy ion sources. New techniques in genomics, proteomics, metabolomics and other “omics” areas should also be intelligently employed and correlated with phenotypic observations. This approach will more precisely elucidate the effects of space radiation on human physiology and aid in developing personalized radiological countermeasures for astronauts. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
Open AccessReview Río Tinto: A Geochemical and Mineralogical Terrestrial Analogue of Mars
Life 2014, 4(3), 511-534; doi:10.3390/life4030511
Received: 8 July 2014 / Revised: 22 August 2014 / Accepted: 28 August 2014 / Published: 15 September 2014
Cited by 7 | PDF Full-text (2068 KB) | HTML Full-text | XML Full-text
Abstract
The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic [...] Read more.
The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic heavy metals), but also in maintaining the high level of microbial diversity detected in the basin. It has been proven that the extreme acidic conditions of Río Tinto basin are not the product of 5000 years of mining activity in the area, but the consequence of an active underground bioreactor that obtains its energy from the massive sulfidic minerals existing in the Iberian Pyrite Belt. Two drilling projects, MARTE (Mars Astrobiology Research and Technology Experiment) (2003–2006) and IPBSL (Iberian Pyrite Belt Subsurface Life Detection) (2011–2015), were developed and carried out to provide evidence of subsurface microbial activity and the potential resources that support these activities. The reduced substrates and the oxidants that drive the system appear to come from the rock matrix. These resources need only groundwater to launch diverse microbial metabolisms. The similarities between the vast sulfate and iron oxide deposits on Mars and the main sulfide bioleaching products found in the Tinto basin have given Río Tinto the status of a geochemical and mineralogical Mars terrestrial analogue. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)

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