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Life
Volume 4
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Life, Volume 4, Issue 1 (March 2014) – 7 articles , Pages 1-116

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565 KiB  
Article
Neuronal Activity in the Subthalamic Cerebrovasodilator Area under Partial-Gravity Conditions in Rats
by Zeredo L Zeredo, Kazuo Toda and Yasuhiro Kumei
Life 2014, 4(1), 107-116; https://doi.org/10.3390/life4010107 - 4 Mar 2014
Cited by 3 | Viewed by 6721
Abstract
The reduced-gravity environment in space is known to cause an upward shift in body fluids and thus require cardiovascular adaptations in astronauts. In this study, we recorded in rats the neuronal activity in the subthalamic cerebrovasodilator area (SVA), a key area that controls [...] Read more.
The reduced-gravity environment in space is known to cause an upward shift in body fluids and thus require cardiovascular adaptations in astronauts. In this study, we recorded in rats the neuronal activity in the subthalamic cerebrovasodilator area (SVA), a key area that controls cerebral blood flow (CBF), in response to partial gravity. “Partial gravity” is the term that defines the reduced-gravity levels between 1 g (the unit gravity acceleration on Earth) and 0 g (complete weightlessness in space). Neuronal activity was recorded telemetrically through chronically implanted microelectrodes in freely moving rats. Graded levels of partial gravity from 0.4 g to 0.01 g were generated by customized parabolic-flight maneuvers. Electrophysiological signals in each partial-gravity phase were compared to those of the preceding 1 g level-flight. As a result, SVA neuronal activity was significantly inhibited by the partial-gravity levels of 0.15 g and lower, but not by 0.2 g and higher. Gravity levels between 0.2–0.15 g could represent a critical threshold for the inhibition of neurons in the rat SVA. The lunar gravity (0.16 g) might thus trigger neurogenic mechanisms of CBF control. This is the first study to examine brain electrophysiology with partial gravity as an experimental parameter. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
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Figure 1

Figure 1
<p>Scheme of parabolic maneuver. The pull-up phase of the parabola was set to generate a mild hypergravity of 1.3 g in order to minimize the any possible physiological response to hypergravity exposure in the animals.</p> Full article ">Figure 2
<p>Schematic drawing of the electrodes position. Histological sections each of the brains were superimposed with the corresponding drawing from the Paxinos Atlas, confirming the electrode position within the subthalamic cerebrovasodilator area (SVA). Arrow indicates blue dots representing the center of electrolytic lesions by an anodal current (0.3 mA, 20 s) passed through the recording electrode. PR: prerubral field, F: fields of Forel, ZI: zona incerta, 3V: thirdventricle, LV: lateral ventricle.</p> Full article ">Figure 3
<p>Neuronal activity in the rat SVA during parabolic flight. Sample waveforms are shown in light-gray with template-matched unit spikes shown in black. From the top, samples from the same animal at partial-gravity levels 0.40, 0.20, 0.15, and 0.05 g are shown. Top inset tracing shows 10 superimposed consecutive spikes from the targeted template. The parabolic flight was composed of stable 1 g straight-and-level flight (baseline data), 1.3g pull-up phase, partial-gravity phase (variable), and 1.3g recovery phase.</p> Full article ">
291 KiB  
Editorial
Acknowledgement to Reviewers of Life in 2013
by Life Editorial Office
Life 2014, 4(1), 105-106; https://doi.org/10.3390/life4010105 - 27 Feb 2014
Viewed by 3942
Abstract
The editors of Life would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article
1850 KiB  
Review
Anaerobic Thermophiles
by Francesco Canganella and Juergen Wiegel
Life 2014, 4(1), 77-104; https://doi.org/10.3390/life4010077 - 26 Feb 2014
Cited by 62 | Viewed by 18295
Abstract
The term “extremophile” was introduced to describe any organism capable of living and growing under extreme conditions. With the further development of studies on microbial ecology and taxonomy, a variety of “extreme” environments have been found and an increasing number of extremophiles are [...] Read more.
The term “extremophile” was introduced to describe any organism capable of living and growing under extreme conditions. With the further development of studies on microbial ecology and taxonomy, a variety of “extreme” environments have been found and an increasing number of extremophiles are being described. Extremophiles have also been investigated as far as regarding the search for life on other planets and even evaluating the hypothesis that life on Earth originally came from space. The first extreme environments to be largely investigated were those characterized by elevated temperatures. The naturally “hot environments” on Earth range from solar heated surface soils and water with temperatures up to 65 °C, subterranean sites such as oil reserves and terrestrial geothermal with temperatures ranging from slightly above ambient to above 100 °C, to submarine hydrothermal systems with temperatures exceeding 300 °C. There are also human-made environments with elevated temperatures such as compost piles, slag heaps, industrial processes and water heaters. Thermophilic anaerobic microorganisms have been known for a long time, but scientists have often resisted the belief that some organisms do not only survive at high temperatures, but actually thrive under those hot conditions. They are perhaps one of the most interesting varieties of extremophilic organisms. These microorganisms can thrive at temperatures over 50 °C and, based on their optimal temperature, anaerobic thermophiles can be subdivided into three main groups: thermophiles with an optimal temperature between 50 °C and 64 °C and a maximum at 70 °C, extreme thermophiles with an optimal temperature between 65 °C and 80 °C, and finally hyperthermophiles with an optimal temperature above 80 °C and a maximum above 90 °C. The finding of novel extremely thermophilic and hyperthermophilic anaerobic bacteria in recent years, and the fact that a large fraction of them belong to the Archaea has definitely made this area of investigation more exciting. Particularly fascinating are their structural and physiological features allowing them to withstand extremely selective environmental conditions. These properties are often due to specific biomolecules (DNA, lipids, enzymes, osmolites, etc.) that have been studied for years as novel sources for biotechnological applications. In some cases (DNA-polymerase, thermostable enzymes), the search and applications successful exceeded preliminary expectations, but certainly further exploitations are still needed. Full article
(This article belongs to the Special Issue Extremophiles and Extreme Environments)
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Figure 1

Figure 1
<p>Phylogenetic tree highlighting possible evolutionary relatedness of anaerobic thermophilic Archaea (modified from Eric Gaba, NASA Astrobiology Institute 2006).</p> Full article ">Figure 2
<p>Some environments where anaerobic thermophiles can be isolated: (<b>a</b>) A power plant in Iceland; (<b>b</b>) Terrestrial hot springs at Viterbo (Italy); (<b>c</b>) The hot pool of Bagno Vignoni (Italy).</p> Full article ">Figure 3
<p>Deep-sea hot ecosystems: (<b>a</b>) Hot sediment at the Guaymas Basin; (<b>b</b>,<b>c</b>) Drawings of black smokers located at a deep-sea hydrothermal vent area (courtesy of Focus Magazine and Jack Jones, respectively).</p> Full article ">
112 KiB  
Review
On the Response of Halophilic Archaea to Space Conditions
by Stefan Leuko, Petra Rettberg, Ashleigh L. Pontifex and Brendan P. Burns
Life 2014, 4(1), 66-76; https://doi.org/10.3390/life4010066 - 21 Feb 2014
Cited by 20 | Viewed by 9464
Abstract
Microorganisms are ubiquitous and can be found in almost every habitat and ecological niche on Earth. They thrive and survive in a broad spectrum of environments and adapt to rapidly changing external conditions. It is of great interest to investigate how microbes adapt [...] Read more.
Microorganisms are ubiquitous and can be found in almost every habitat and ecological niche on Earth. They thrive and survive in a broad spectrum of environments and adapt to rapidly changing external conditions. It is of great interest to investigate how microbes adapt to different extreme environments and with modern human space travel, we added a new extreme environment: outer space. Within the last 50 years, technology has provided tools for transporting microbial life beyond Earth’s protective shield in order to study in situ responses to selected conditions of space. This review will focus on halophilic archaea, as, due to their ability to survive in extremes, they are often considered a model group of organisms to study responses to the harsh conditions associated with space. We discuss ground-based simulations, as well as space experiments, utilizing archaea, examining responses and/or resistance to the effects of microgravity and UV in particular. Several halophilic archaea (e.g., Halorubrum chaoviator) have been exposed to simulated and actual space conditions and their survival has been determined as well as the protective effects of halite shown. Finally, the intriguing potential of archaea to survive on other planets or embedded in a meteorite is postulated. Full article
(This article belongs to the Special Issue Response of Terrestrial Life to Space Conditions)
383 KiB  
Review
Setting the Stage for Habitable Planets
by Guillermo Gonzalez
Life 2014, 4(1), 35-65; https://doi.org/10.3390/life4010035 - 21 Feb 2014
Cited by 2 | Viewed by 9106
Abstract
Our understanding of the processes that are relevant to the formation and maintenance of habitable planetary systems is advancing at a rapid pace, both from observation and theory. The present review focuses on recent research that bears on this topic and includes discussions [...] Read more.
Our understanding of the processes that are relevant to the formation and maintenance of habitable planetary systems is advancing at a rapid pace, both from observation and theory. The present review focuses on recent research that bears on this topic and includes discussions of processes occurring in astrophysical, geophysical and climatic contexts, as well as the temporal evolution of planetary habitability. Special attention is given to recent observations of exoplanets and their host stars and the theories proposed to explain the observed trends. Recent theories about the early evolution of the Solar System and how they relate to its habitability are also summarized. Unresolved issues requiring additional research are pointed out, and a framework is provided for estimating the number of habitable planets in the Universe. Full article
(This article belongs to the Special Issue Planet Formation and the Rise of Life)
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Figure 1

Figure 1
<p>Figure 4 from [<a href="#B86-life-04-00035" class="html-bibr">86</a>] based on Kepler observations of small planets. The green box contains the planets most similar in size and received stellar insolation to Earth.</p> Full article ">Figure 2
<p>Figure 3 from [<a href="#B88-life-04-00035" class="html-bibr">88</a>] showing the radii and masses of well-characterized exoplanets as red open circles. Modeled mass-radius curves for various pure compositions are shown as blue curves. Solar System planets are shown as green triangles. Figure courtesy of Andrew W. Howard.</p> Full article ">Figure 3
<p>Eccentricity distribution of 394 exoplanets with orbital periods greater than 20 days from the vetted data in the Exoplanet Orbit Database. The median value of the distribution is 0.18.</p> Full article ">
11412 KiB  
Article
The Formation of Jupiter, the Jovian Early Bombardment and the Delivery of Water to the Asteroid Belt: The Case of (4) Vesta
by Diego Turrini and Vladimir Svetsov
Life 2014, 4(1), 4-34; https://doi.org/10.3390/life4010004 - 28 Jan 2014
Cited by 20 | Viewed by 7789
Abstract
The asteroid (4) Vesta, parent body of the Howardite-Eucrite-Diogenite meteorites, is one of the first bodies that formed, mostly from volatile-depleted material, in the Solar System. The Dawn mission recently provided evidence that hydrated material was delivered to Vesta, possibly in a continuous [...] Read more.
The asteroid (4) Vesta, parent body of the Howardite-Eucrite-Diogenite meteorites, is one of the first bodies that formed, mostly from volatile-depleted material, in the Solar System. The Dawn mission recently provided evidence that hydrated material was delivered to Vesta, possibly in a continuous way, over the last 4 Ga, while the study of the eucritic meteorites revealed a few samples that crystallized in presence of water and volatile elements. The formation of Jupiter and probably its migration occurred in the period when eucrites crystallized, and triggered a phase of bombardment that caused icy planetesimals to cross the asteroid belt. In this work, we study the flux of icy planetesimals on Vesta during the Jovian Early Bombardment and, using hydrodynamic simulations, the outcome of their collisions with the asteroid. We explore how the migration of the giant planet would affect the delivery of water and volatile materials to the asteroid and we discuss our results in the context of the geophysical and collisional evolution of Vesta. In particular, we argue that the observational data are best reproduced if the bulk of the impactors was represented by 1–2 km wide planetesimals and if Jupiter underwent a limited (a fraction of au) displacement. Full article
(This article belongs to the Special Issue Planet Formation and the Rise of Life)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Formation of the crater and evolution of the projectile’s material after the impact on Vesta of a OSS planetesimal with a velocity 4 km/s and diameter of 1 km. Isolines of density are shown in the plane XY passing through the vector of impact velocity and the center of Vesta. The crustal material of Vesta with density above 0.5 g/cm<sup>3</sup> is shown by the grey color. The material of the impactor is indicated in blue. The red arrow in the first panel shows the direction of the impact (45° respect to the local vertical). Note the different scales on the axes in the four panels.</p> Full article ">Figure 2
<p>Distributions of the material of the impactors over the vestan surface after the impacts of OSS planetesimals with diameter of 1 km at 4 km/s (<b>left</b> plots) and at 8 km/s (<b>right</b> plots). The upper panels show the hemisphere where the impacts occurred, with the center of the craters in the middle of the hemisphere. The lower panels show instead the opposite hemisphere. The impacting bodies strike Vesta along the positive direction of the X axis at 45° respect to the local vertical.</p> Full article ">Figure 3
<p>Erosion (<b>left</b> plot) and accretion (<b>right</b> plot) efficiencies of cometary impactors on Vesta, expressed in units of the mass of the impactors. The plotted values are from <a href="#t1-life-04-00004" class="html-table">Table 1</a>.</p> Full article ">Figure 4
<p>The orbital structure of the protoplanetary disk 2 × 10<sup>5</sup> years after Jupiter started to accrete the nebular gas (<span class="html-italic">i.e.</span>, 1.2 × 10<sup>6</sup> years from the beginning of the simulations). The black symbols at 2.36 au and at 5.2 au indicate respectively Vesta and Jupiter. The open circles in the cases of 0.25 au, 0.50 au and 1.00 au migration indicate the initial position of Jupiter. ISS impactors are indicated in red, OSS impactors in blue.</p> Full article ">Figure 5
<p>Normalized distribution of the impact velocities of OSS impactors reported in Paper I in the four migration scenarios. The distribution of the impact velocities is common to all SFDs of the impactors.</p> Full article ">Figure 6
<p>Size-frequency distributions of the OSS impactors on Vesta in the four migration scenarios for the different SFDs of the primordial asteroids considered in this work. Numbers of impacts lower than 1 indicate stochastic events (even when considered cumulatively): these cases are not considered in the following analysis.</p> Full article ">Figure 7
<p>Mass loss of Vesta in the different migration scenarios and for the different SFDs considered. The mass loss is expressed in units of the present Vestan mass ([<a href="#b32-life-04-00004" class="html-bibr">32</a>,<a href="#b52-life-04-00004" class="html-bibr">52</a>]).</p> Full article ">Figure 8
<p>Surface erosion of Vesta in the different migration scenarios and for the different SFDs considered. Surface erosion is expressed as the thickness of a shell, with density equal to the present crustal one of Vesta and mass equal to the eroded mass, extending from the present radius of Vesta outwards. The plot on the left shows the case of a uniform erosion, the plot on the right shows instead the case of erosion proportional to the cross-sectional area of Vesta. The dotted line indicates the thickness of the eucritic layer according to [<a href="#b12-life-04-00004" class="html-bibr">12</a>].</p> Full article ">Figure 9
<p>R-plots of the crater populations produced by the different SFDs of the OSS planetesimals in the four migration scenarios. The 5% and 13% saturation levels and the crater population caused by the last 4 Ga of collisional evolution of Vesta are also shown for reference. The light blue vertical dashed line indicates the present diameter of Vesta.</p> Full article ">Figure 10
<p>Amounts of volatile materials (expressed in units of the present vestan mass, [<a href="#b32-life-04-00004" class="html-bibr">32</a>]) delivered by the OSS impactors to Vesta in the four migration scenarios and for the four SFDs we considered. Also indicated, as the horizontal dotted line, is the fraction of the Earth’s mass represented by water (5 × 10<sup>−4</sup>, [<a href="#b64-life-04-00004" class="html-bibr">64</a>]).</p> Full article ">Figure 11
<p>R-plot of the excavation depth of craters on Vesta across the JEB for the different SFDs and migration scenarios considered in this work. The 5% and 13% saturation levels are shown for reference. The vertical light blue dashed line indicates the thickness of the crust of Vesta (<span class="html-italic">i.e.</span>, the eucritic and diogenitic layers) as estimated by [<a href="#b12-life-04-00004" class="html-bibr">12</a>].</p> Full article ">
23 KiB  
Editorial
Letter from the New Editor-in-Chief
by Pabulo Henrique Rampelotto
Life 2014, 4(1), 1-3; https://doi.org/10.3390/life4010001 - 8 Jan 2014
Cited by 5 | Viewed by 6019
Abstract
It is my great pleasure to serve as the new Editor-in-Chief of Life, a journal concerned with fundamental questions on the origins and nature of life, evolution of biosystems and astrobiology. With my experience as Executive Editor, Senior Editor and Guest Editor of [...] Read more.
It is my great pleasure to serve as the new Editor-in-Chief of Life, a journal concerned with fundamental questions on the origins and nature of life, evolution of biosystems and astrobiology. With my experience as Executive Editor, Senior Editor and Guest Editor of so many successful special issues (some of them in MDPI journals [1–6]), I am committed to making the journal a success, with the launch of exciting special issues, publication of high quality papers, as well as inclusion of the journal in major indexing and abstracting services. In this editorial, I present my view and plans for the journal. [...] Full article
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