90 research outputs found
Proton radii of Be, B, and C isotopes
We investigate the neutron number dependence of root mean square radii
of point proton distribution (proton radii) of Be, B, and C isotopes with the
theoretical method of variation after spin-parity projection in the framework
of antisymmetrized molecular dynamics (AMD). The proton radii in Be and B
isotopes changes rapidly as increases, reflecting the cluster structure
change along the isotope chains, whereas, those in C isotopes show a weak
dependence because of the stable proton structure in nuclei with . In
neutron-rich Be and B isotopes, the proton radii are remarkably increased by
the enhancement of the two-center cluster structure in the prolately deformed
neutron structure. We compare the dependence of the calculated proton radii
with the experimental ones reduced from the charge radii determined by isotope
shift and those deduced from the charge changing interaction cross section. It
is found that the dependence of proton radii can be a probe to clarify
enhancement and weakening of cluster structures.Comment: 13 pages, 8 figure
Microbial iron reduction on Earth and Mars
The search for life beyond Earth is the driving force behind several future missions
to Mars. An essential task in the lead-up to these missions is a critical assessment of the
habitability for, and feasibility of, life. However, little research has been conducted on this
issue, and our understanding of the plausibility for life on Mars remains unconstrained.
Owing to the anoxic and iron-rich nature of Mars, microbial iron reduction (MIR) represents
a compelling candidate metabolism to operate in the Martian subsurface, past and present.
The objectives of this thesis are to address the feasibility of MIR on Mars by i) better
defining the habitability of MIR on Earth, and ii) assessing the range and availability of
organic electron donors in the subsurface of Earth and Mars.
Samples collected from Mars-relevant environments on Earth were used to initiate
MIR enrichment cultures at 4°C, 15°C and 30°C. Results indicate MIR is widespread in
riverbed and subglacial sediments but not sediments from desert or recent volcanic plains.
The iron-reducing microorganisms in subglacial enrichments are at least psychrotolerant and
in some cases psychrophilc. Culture-independent methods highlighted the changes in
diversity between temperature conditions for subglacial sediments, and indicated that
members of the prolific MIR Geobacteraceae family are common. The genera Geobacter
and Desulfosporosinus are responsible for MIR in the majority of enrichments. Long-term
anoxia and the availability of redox constituents are the major factors controlling MIR in
these environments.
A MIR enrichment culture was unable to use shales and kerogens as the sole source
of electron donors for MIR, despite the presence of known electron donors. Furthermore,
MIR was inhibited by the presence of certain kerogens. The causes of inhibition are
unknown, and are likely to be a combination of chemical and physical factors.
Experiments were conducted to assess the ability of three pure strains and a MIR
enrichment to use non-proteinogenic amino acids common to carbonaceous meteorites as
electron donors for MIR. Results demonstrate that γ-aminobutyric acid served as an electron
donor for the enrichment culture, but no other amino acids supported MIR by this or other
iron-reducing cultures. The D-form of chiral amino acids was found to exert a strong
inhibitory effect, which decreased in line with concentration. Theoretical calculations using
published meteoritic accretion rates onto the surface of Mars indicate that the build up
inhibitory amino acids may place important constrains on habitability over geologic time
scales.
Contamination of a pure strain of Geobacter metallireducens with a strain of
Clostridium revealed a syntrophic relationship between these microorganisms. Anaerobic
heterotrophs are likely to play an important role in maintaining an available supply of
electron donors for MIR and similar chemoorganic metabolisms operating in the subsurface.
This research indicates that MIR remains a feasible metabolism to operate on Mars providing
a readily available redox couple is present. However, given the observed inhibition in the
presence of bulk carbonaceous material and certain amino acids found in meteorites, the use
of extraterrestrial carbonaceous material in the Martian subsurface for microbial iron
reduction is questionable, and should be the focus of future researc
Light and Life: Exotic Photosynthesis in Binary Star Systems
The potential for hosting photosynthetic life on Earth-like planets within
binary/multiple stellar systems was evaluated by modelling the levels of
photosynthetically active radiation (PAR) such planets receive. Combinations of
M and G stars in: (i) close-binary systems; (ii) wide-binary systems and (iii)
three-star systems were investigated and a range of stable radiation
environments found to be possible. These environmental conditions allow for the
possibility of familiar, but also more exotic forms of photosynthetic life,
such as infrared photosynthesisers and organisms specialised for specific
spectral niches.Comment: Accepted for publication in: Astrobiolog
Detection of single cell microbial life artificially inoculated in mudstone analogue material using a miniature LIMS system
Stars and planetary system
Detectability of biosignatures in a low-biomass simulation of martian sediments
Discovery of a remnant habitable environment by the Mars Science Laboratory in the sedimentary record of Gale Crater has reinvigorated the search for evidence of martian life. In this study, we used a simulated martian mudstone material, based on data from Gale Crater, that was inoculated and cultured over several months and then dried and pressed. The simulated mudstone was analysed with a range of techniques to investigate the detectability of biosignatures. Cell counting and DNA extraction showed a diverse but low biomass microbial community that was highly dispersed. Pellets were analysed with bulk Elemental Analysis - Isotope Ratio Mass Spectrometry (EA-IRMS), high-resolution Laser-ablation Ionisation Mass Spectrometry (LIMS), Raman spectroscopy and Fourier Transform InfraRed (FTIR) spectroscopy, which are all techniques of relevance to current and future space missions. Bulk analytical techniques were unable to differentiate between inoculated samples and abiotic controls, despite total levels of organic carbon comparable with that of the martian surface. Raman spectroscopy, FTIR spectroscopy and LIMS, which are high sensitivity techniques that provide chemical information at high spatial resolution, retrieved presumptive biosignatures but these remained ambiguous and the sedimentary matrix presented challenges for all techniques. This suggests challenges for detecting definitive evidence for life, both in the simulated lacustrine environment via standard microbiological techniques and in the simulated mudstone via analytical techniques with relevance to robotic missions. Our study suggests that multiple co-incident high-sensitivity techniques that can scan the same micrometre-scale spots are required to unambiguously detect biosignatures, but the spatial coverage of these techniques needs to be high enough not to miss individual cellular-scale structures in the matrix
The UK Centre for Astrobiology:A Virtual Astrobiology Centre. Accomplishments and Lessons Learned, 2011-2016
Authors thank all those individuals, UK research councils, funding agencies, nonprofit organisations, companies and corporations and UK and non-UK government agencies, who have so generously supported our aspirations and hopes over the last 5 years and supported UKCA projects. They include the STFC, the Engineering and Physical Sciences Research Council (EPSRC), the Natural Environmental Research Council (NERC), the EU, the UK Space Agency, NASA, the European Space Agency (ESA), The Crown Estate, Cleveland Potash and others. The Astrobiology Academy has been supported by the UK Space Agency (UKSA), National Space Centre, the Science and Technology Facilities Council (STFC), Dynamic Earth, The Royal Astronomical Society, The Rotary Club (Shetlands) and the NASA Astrobiology Institute.The UK Centre for Astrobiology (UKCA) was set up in 2011 as a virtual center to contribute to astrobiology research, education, and outreach. After 5 years, we describe this center and its work in each of these areas. Its research has focused on studying life in extreme environments, the limits of life on Earth, and implications for habitability elsewhere. Among its research infrastructure projects, UKCA has assembled an underground astrobiology laboratory that has hosted a deep subsurface planetary analog program, and it has developed new flow-through systems to study extraterrestrial aqueous environments. UKCA has used this research backdrop to develop education programs in astrobiology, including a massive open online course in astrobiology that has attracted over 120,000 students, a teacher training program, and an initiative to take astrobiology into prisons. In this paper, we review these activities and others with a particular focus on providing lessons to others who may consider setting up an astrobiology center, institute, or science facility. We discuss experience in integrating astrobiology research into teaching and education activities.Publisher PDFPeer reviewe
Habitable Zones and UV Habitable Zones around Host Stars
Ultraviolet radiation is a double-edged sword to life. If it is too strong,
the terrestrial biological systems will be damaged. And if it is too weak, the
synthesis of many biochemical compounds can not go along. We try to obtain the
continuous ultraviolet habitable zones, and compare the ultraviolet habitable
zones with the habitable zones of host stars. Using the boundary ultraviolet
radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable
zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with
effective temperatures lower than 4,600 K, the ultraviolet habitable zones are
closer than the habitable zones. For the host stars with effective temperatures
higher than 7,137 K, the ultraviolet habitable zones are farther than the
habitable zones. For hot subdwarf as a host star, the distance of the
ultraviolet habitable zone is about ten times more than that of the habitable
zone, which is not suitable for life existence.Comment: 5 pages, 3 figure
Microbial life in the nascent Chicxulub crater
The Chicxulub crater was formed by an asteroid impact at ca. 66 Ma. The impact is considered to have contributed to the end-Cretaceous mass extinction and reduced productivity in the world's oceans due to a transient cessation of photosynthesis. Here, biomarker profiles extracted from crater core material reveal exceptional insights into the post-impact upheaval and rapid recovery of microbial life. In the immediate hours to days after the impact, ocean resurge flooded the crater and a subsequent tsunami delivered debris from the surrounding carbonate ramp. Deposited material, including biomarkers diagnostic for land plants, cyanobacteria, and photosynthetic sulfur bacteria, appears to have been mobilized by wave energy from coastal microbial mats. As that energy subsided, days to months later, blooms of unicellular cyanobacteria were fueled by terrigenous nutrients. Approximately 200 k.y. later, the nutrient supply waned and the basin returned to oligotrophic conditions, as evident from N2-fixing cyanobacteria biomarkers. At 1 m.y. after impact, the abundance of photosynthetic sulfur bacteria supported the development of water-column photic zone euxinia within the crater
Microbial Metabolism of Amino Acids—Biologically Induced Removal of Glycine and the Resulting Fingerprint as a Potential Biosignature
The identification of reliable biomarkers, such as amino acids, is key for the search of extraterrestrial life. A large number of microorganisms metabolize, synthesize, take up and excrete amino acids as part of the amino acid metabolism during aerobic and/or anaerobic respiration or in fermentation. In this work, we investigated whether the anaerobic microbial metabolism of amino acids could leave a secondary biosignature indicating biological activity in the environment around the cells. The observed fingerprints would reflect the physiological capabilities of the specific microbial community under investigation. The
metabolic processing of an amino acid mixture by two distinct anaerobic microbial communities collected from Islinger Mühlbach (ISM) and Sippenauer Moor (SM), Germany was examined. The amino acid mixture contained L-alanine, β-alanine, L-aspartic acid, DL-proline, L-leucine, L-valine, glycine, L-phenylalanine and L-isoleucine. In parallel, an amino acid spiked medium without microorganisms was used as a control to determine abiotic changes over time. Liquid chromatography mass spectrometry (LC-MS) was used to track amino acid changes over time. When comparing to the control samples that did not show significant changes of amino acids concentrations over time, we found that glycine was almost completely depleted from both microbial samples to less than 3% after the first two weeks- This results indicates a preferential use of this simple amino acid by these microbial communities. Although glycine
degradation can be caused by abiotic processes, these results show that its preferential depletion in an environment would be consistent with the presence of life. We found changes in most other amino acids that varied between amino acids and communities, suggesting complex dynamics with no clear universal pattern that might be used as a signature of life. However, marked increases in amino acids, caused by cellular synthesis and release into the extracellular environment (e.g., alanine), were observed and could be considered a signature of metabolic activity. We conclude, that substantial anomalous enhancements of some amino acids against the expected abiotic background concentration may be an agnostic signature of the presence of biological processes
MICROORGANISMS FROM MARS ANALOGUE ENVIRONMENTS IN EARTH - COULD THEY SURVIVE ON MARS?
Assessing the habitability of Mars and detecting life, if it was ever there, depends on knowledge
of whether the combined environmental stresses experienced on Mars are compatible with life
and whether a record of that life could ever be detected. Many combinations of Mars relevant
stress factors, such as high radiation dose rates and high UV
uences combined with high salt
concentrations, and low water activity, have not been investigated. In particular, the response
of anaerobic organisms to Mars-like stress factors and combinations thereof are not known. In
the EC project MASE (Mars Analogues for Space Exploration) we address these limitations by
characterising different Mars analogue environments on Earth, isolating microorganisms from
these sites and exposing them to Mars relevant stress factors alone and in combination. We
want to find out, if these bacteria respond in an additive or synergistic way and if they would
be able to survive on Mars. So far, eight only distantly related microorganisms are under
detailed investigation, e.g Yersinia sp., Halanaerobium sp., Acidiphilum sp. Desulfovibrio sp..
Unexpectedly, a Yersinia strain turned out to be quite resistant, especially against desicca-
tion and oxidising compounds, whereas a Desulfovibrio sp. strain exhibit a relatively high
radiation resistance. The future experiments aim at the identification of the underlying cellu-
lar and molecular mechanisms and the comparison to other new isolates from Mars analogue
environments on Earth in the MASE project
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