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Life
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Microbial Life in the Solar System
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Microbial Life in the Solar System

A special issue of Life (ISSN 2075-1729). This special issue belongs to the section "Astrobiology".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 22446

Special Issue Editor

Dr. Jay Nadeau

E-Mail Website
Guest Editor
Physics Department, Portland State University, Portland, OR 97207, USA
Interests: digital holographic microscopy; nanomaterials; astrobiology; scintillating materials

Special Issue Information

Dear Colleagues,

I would like to invite you to submit a paper to a Special Issue of the journal Life, on the subject of “Microbial Life in the Solar System.” The goal of this Special Issue is to bring together discussions of the possible distribution and prevalence of microbial life elsewhere in Earth’s Solar System, biosignatures of extant and/or extinct life, techniques for detection of such biosignatures, and mission considerations. Energetic considerations for the existence of life on specific extraterrestrial bodies and the possibility of non-water-based biochemistries are of particular interest. Papers discussing analog sites on Earth are also welcomed.

Dr. Jay Nadeau
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Life is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • astrobiology
  • Europa
  • Enceladus
  • Venus
  • Mars
  • Titan
  • extraterrestrial life
  • biosignature
  • ocean worlds

Published Papers (7 papers)

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Research

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14 pages, 1450 KiB  
Article
Enceladus as a Potential Niche for Methanogens and Estimation of Its Biomass
by Laura I. Tenelanda-Osorio, Juan L. Parra, Pablo Cuartas-Restrepo and Jorge I. Zuluaga
Life 2021, 11(11), 1182; https://0-doi-org.brum.beds.ac.uk/10.3390/life11111182 - 05 Nov 2021
Cited by 5 | Viewed by 2619
Abstract
Enceladus is a potential target for future astrobiological missions. NASA’s Cassini spacecraft demonstrated that the Saturnian moon harbors a salty ocean beneath its icy crust and the existence and analysis of the plume suggest water–rock reactions, consistent with the possible presence of hydrothermal [...] Read more.
Enceladus is a potential target for future astrobiological missions. NASA’s Cassini spacecraft demonstrated that the Saturnian moon harbors a salty ocean beneath its icy crust and the existence and analysis of the plume suggest water–rock reactions, consistent with the possible presence of hydrothermal vents. Particularly, the plume analysis revealed the presence of molecular hydrogen, which may be used as an energy source by microorganisms ( e.g., methanogens). This could support the possibility that populations of methanogens could establish in such environments if they exist on Enceladus. We took a macroscale approximation using ecological niche modeling to evaluate whether conditions suitable for methanogenic archaea on Earth are expected in Enceladus. In addition, we employed a new approach for computing the biomass using the Monod growth model. The response curves for the environmental variables performed well statistically, indicating that simple correlative models may be used to approximate large-scale distributions of these genera on Earth. We found that the potential hydrothermal conditions on Enceladus fit within the macroscale conditions identified as suitable for methanogens on Earth, and estimated a concentration of 1010–1011 cells/cm3. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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14 pages, 2413 KiB  
Article
Microscopic Object Classification through Passive Motion Observations with Holographic Microscopy
by Devan Rouzie, Christian Lindensmith and Jay Nadeau
Life 2021, 11(8), 793; https://0-doi-org.brum.beds.ac.uk/10.3390/life11080793 - 05 Aug 2021
Cited by 3 | Viewed by 2171
Abstract
Digital holographic microscopy provides the ability to observe throughout a volume that is large compared to its resolution without the need to actively refocus to capture the entire volume. This enables simultaneous observations of large numbers of small objects within such a volume. [...] Read more.
Digital holographic microscopy provides the ability to observe throughout a volume that is large compared to its resolution without the need to actively refocus to capture the entire volume. This enables simultaneous observations of large numbers of small objects within such a volume. We have constructed a microscope that can observe a volume of 0.4 µm × 0.4 µm × 1.0 µm with submicrometer resolution (in xy) and 2 µm resolution (in z) for observation of microorganisms and minerals in liquid environments on Earth and on potential planetary missions. Because environmental samples are likely to contain mixtures of inorganics and microorganisms of comparable sizes near the resolution limit of the instrument, discrimination between living and non-living objects may be difficult. The active motion of motile organisms can be used to readily distinguish them from non-motile objects (live or inorganic), but additional methods are required to distinguish non-motile organisms and inorganic objects that are of comparable size but different composition and structure. We demonstrate the use of passive motion to make this discrimination by evaluating diffusion and buoyancy characteristics of cells, styrene beads, alumina particles, and gas-filled vesicles of micron scale in the field of view. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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18 pages, 2782 KiB  
Article
Use of NanoSIMS to Identify the Lower Limits of Metabolic Activity and Growth by Serratia liquefaciens Exposed to Sub-Zero Temperatures
by Petra Schwendner, Ann N. Nguyen and Andrew C. Schuerger
Life 2021, 11(5), 459; https://0-doi-org.brum.beds.ac.uk/10.3390/life11050459 - 20 May 2021
Viewed by 2689
Abstract
Serratia liquefaciens is a cold-adapted facultative anaerobic astrobiology model organism with the ability to grow at a Martian atmospheric pressure of 7 hPa. Currently there is a lack of data on its limits of growth and metabolic activity at sub-zero temperatures found in [...] Read more.
Serratia liquefaciens is a cold-adapted facultative anaerobic astrobiology model organism with the ability to grow at a Martian atmospheric pressure of 7 hPa. Currently there is a lack of data on its limits of growth and metabolic activity at sub-zero temperatures found in potential habitable regions on Mars. Growth curves and nano-scale secondary ion mass spectrometry (NanoSIMS) were used to characterize the growth and metabolic threshold for S. liquefaciens ATCC 27,592 grown at and below 0 °C. Cells were incubated in Spizizen medium containing three stable isotopes substituting their unlabeled counterparts; i.e., 13C-glucose, (15NH4)2SO4, and H218O; at 0, −1.5, −3, −5, −10, or −15 °C. The isotopic ratios of 13C/12C, 15N/14N, and 18O/16O and their corresponding fractions were determined for 240 cells. NanoSIMS results revealed that with decreasing temperature the cellular amounts of labeled ions decreased indicating slower metabolic rates for isotope uptake and incorporation. Metabolism was significantly reduced at −1.5 and −3 °C, almost halted at −5 °C, and shut-down completely at or below −10 °C. While growth was observed at 0 °C after 5 days, samples incubated at −1.5 and −3 °C exhibited significantly slower growth rates until growth was detected at 70 days. In contrast, cell densities decreased by at least half an order of magnitude over 70 days in cultures incubated at ≤ −5 °C. Results suggest that S. liquefaciens, if transported to Mars, might be able to metabolize and grow in shallow sub-surface niches at temperatures above −5 °C and might survive—but not grow—at temperatures below −5 °C. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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11 pages, 719 KiB  
Communication
The Case (or Not) for Life in the Venusian Clouds
by Dirk Schulze-Makuch
Life 2021, 11(3), 255; https://0-doi-org.brum.beds.ac.uk/10.3390/life11030255 - 20 Mar 2021
Cited by 8 | Viewed by 5198
Abstract
The possible detection of the biomarker of phosphine as reported by Greaves et al. in the Venusian atmosphere stirred much excitement in the astrobiology community. While many in the community are adamant that the environmental conditions in the Venusian atmosphere are too extreme [...] Read more.
The possible detection of the biomarker of phosphine as reported by Greaves et al. in the Venusian atmosphere stirred much excitement in the astrobiology community. While many in the community are adamant that the environmental conditions in the Venusian atmosphere are too extreme for life to exist, others point to the claimed detection of a convincing biomarker, the conjecture that early Venus was doubtlessly habitable, and any Venusian life might have adapted by natural selection to the harsh conditions in the Venusian clouds after the surface became uninhabitable. Here, I first briefly characterize the environmental conditions in the lower Venusian atmosphere and outline what challenges a biosphere would face to thrive there, and how some of these obstacles for life could possibly have been overcome. Then, I discuss the significance of the possible detection of phosphine and what it means (and does not mean) and provide an assessment on whether life may exist in the temperate cloud layer of the Venusian atmosphere or not. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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Review

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15 pages, 12065 KiB  
Review
Extant Earthly Microbial Mats and Microbialites as Models for Exploration of Life in Extraterrestrial Mat Worlds
by Bopaiah Biddanda, Anthony Weinke, Ian Stone, Scott Kendall, Phil Hartmeyer, Wayne Lusardi, Stephanie Gandulla, John Bright and Steven Ruberg
Life 2021, 11(9), 883; https://0-doi-org.brum.beds.ac.uk/10.3390/life11090883 - 27 Aug 2021
Cited by 2 | Viewed by 3857
Abstract
As we expand the search for life beyond Earth, a water-dominated planet, we turn our eyes to other aquatic worlds. Microbial life found in Earth’s many extreme habitats are considered useful analogs to life forms we are likely to find in extraterrestrial bodies [...] Read more.
As we expand the search for life beyond Earth, a water-dominated planet, we turn our eyes to other aquatic worlds. Microbial life found in Earth’s many extreme habitats are considered useful analogs to life forms we are likely to find in extraterrestrial bodies of water. Modern-day benthic microbial mats inhabiting the low-oxygen, high-sulfur submerged sinkholes of temperate Lake Huron (Michigan, USA) and microbialites inhabiting the shallow, high-carbonate waters of subtropical Laguna Bacalar (Yucatan Peninsula, Mexico) serve as potential working models for exploration of extraterrestrial life. In Lake Huron, delicate mats comprising motile filaments of purple-pigmented cyanobacteria capable of oxygenic and anoxygenic photosynthesis and pigment-free chemosynthetic sulfur-oxidizing bacteria lie atop soft, organic-rich sediments. In Laguna Bacalar, lithification by cyanobacteria forms massive carbonate reef structures along the shoreline. Herein, we document studies of these two distinct earthly microbial mat ecosystems and ponder how similar or modified methods of study (e.g., robotics) would be applicable to prospective mat worlds in other planets and their moons (e.g., subsurface Mars and under-ice oceans of Europa). Further studies of modern-day microbial mat and microbialite ecosystems can add to the knowledge of Earth’s biodiversity and guide the search for life in extraterrestrial hydrospheres. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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Other

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14 pages, 33219 KiB  
Hypothesis
Water–Sulfuric Acid Foam as a Possible Habitat for Hypothetical Microbial Community in the Cloud Layer of Venus
by Dmitry A. Skladnev, Sergei P. Karlov, Yuliya Y. Khrunyk and Oleg R. Kotsyurbenko
Life 2021, 11(10), 1034; https://0-doi-org.brum.beds.ac.uk/10.3390/life11101034 - 30 Sep 2021
Cited by 4 | Viewed by 2085
Abstract
The data available at the moment suggest that ancient Venus was covered by extensive bodies of water which could harbor life. Later, however, the drastic overheating of the planet made the surface of Venus uninhabitable for Earth-type life forms. Nevertheless, hypothetical Venusian organisms [...] Read more.
The data available at the moment suggest that ancient Venus was covered by extensive bodies of water which could harbor life. Later, however, the drastic overheating of the planet made the surface of Venus uninhabitable for Earth-type life forms. Nevertheless, hypothetical Venusian organisms could have gradually adapted to conditions within the cloud layer of Venus—the only niche containing liquid water where the Earth-type extremophiles could survive. Here we hypothesize that the unified internal volume of a microbial community habitat is represented by the heterophase liquid-gas foam structure of Venusian clouds. Such unity of internal space within foam water volume facilitates microbial cells movements and trophic interactions between microorganisms that creates favorable conditions for the effective development of a true microbial community. The stabilization of a foam heterophase structure can be provided by various surfactants including those synthesized by living cells and products released during cell lysis. Such a foam system could harbor a microbial community of different species of (poly)extremophilic microorganisms that are capable of photo- and chemosynthesis and may be closely integrated into aero-geochemical processes including the processes of high-temperature polymer synthesis on the planet’s surface. Different complex nanostructures transferred to the cloud layers by convection flows could further contribute to the stabilization of heterophase liquid-gas foam structure and participate in chemical and photochemical reactions, thus supporting ecosystem stability. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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10 pages, 1370 KiB  
Brief Report
Complex Brines and Their Implications for Habitability
by Nilton O. Renno, Erik Fischer, Germán Martínez and Jennifer Hanley
Life 2021, 11(8), 847; https://0-doi-org.brum.beds.ac.uk/10.3390/life11080847 - 19 Aug 2021
Cited by 2 | Viewed by 2182
Abstract
There is evidence that life on Earth originated in cold saline waters around scorching hydrothermal vents, and that similar conditions might exist or have existed on Mars, Europa, Ganymede, Enceladus, and other worlds. Could potentially habitable complex brines with extremely low freezing temperatures [...] Read more.
There is evidence that life on Earth originated in cold saline waters around scorching hydrothermal vents, and that similar conditions might exist or have existed on Mars, Europa, Ganymede, Enceladus, and other worlds. Could potentially habitable complex brines with extremely low freezing temperatures exist in the shallow subsurface of these frigid worlds? Earth, Mars, and carbonaceous chondrites have similar bulk elemental abundances, but while the Earth is depleted in the most volatile elements, the Icy Worlds of the outer solar system are expected to be rich in them. The cooling of ionic solutions containing substances that likely exist in the Icy Worlds could form complex brines with the lowest eutectic temperature possible for the compounds available in them. Indeed, here, we show observational and theoretical evidence that even elements present in trace amounts in nature are concentrated by freeze–thaw cycles, and therefore contribute significantly to the formation of brine reservoirs that remain liquid throughout the year in some of the coldest places on Earth. This is interesting because the eutectic temperature of water–ammonia solutions can be as low as ~160 K, and significant fractions of the mass of the Icy Worlds are estimated to be water substance and ammonia. Thus, briny solutions with eutectic temperature of at least ~160 K could have formed where, historically, temperature have oscillated above and below ~160 K. We conclude that complex brines must exist in the shallow subsurface of Mars and the Icy Worlds, and that liquid saline water should be present where ice has existed, the temperature is above ~160 K, and evaporation and sublimation have been inhibited. Full article
(This article belongs to the Special Issue Microbial Life in the Solar System)
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