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  • 1
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    5S ribosomal ribonucleic acid sequences in Bacteroides and Fusobacterium: evolutionary relationships within these genera and among eubacteria in general (1989)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The 5S ribosomal ribonucleic acid (rRNA) sequences were determined for Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides capillosus, Bacteroides veroralis, Porphyromonas gingivalis, Anaerorhabdus furcosus, Fusobacterium nucleatum, Fusobacterium mortiferum, and Fusobacterium varium. A dendrogram constructed by a clustering algorithm from these sequences, which were aligned with all other hitherto known eubacterial 5S rRNA sequences, showed differences as well as similarities with respect to results derived from 16S rRNA analyses. In the 5S rRNA dendrogram, Bacteroides clustered together with Cytophaga and Fusobacterium, as in 16S rRNA analyses. Intraphylum relationships deduced from 5S rRNAs suggested that Bacteroides is specifically related to Cytophaga rather than to Fusobacterium, as was suggested by 16S rRNA analyses. Previous taxonomic considerations concerning the genus Bacteroides, based on biochemical and physiological data, were confirmed by the 5S rRNA sequence analysis.
    Keywords: Exobiology
    Type: International journal of systematic bacteriology (ISSN 0020-7713); Volume 39; 1; 78-84
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  • 2
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    The Astrobiology Primer v2.0 (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Astrobiology is the science that seeks to understand the story of life in our universe. Astrobiology includes investigation of the conditions that are necessary for life to emerge and flourish, the origin of life, the ways that life has evolved and adapted to the wide range of environmental conditions here on Earth, the search for life beyond Earth, the habitability of extraterrestrial environments, and consideration of the future of life here on Earth and elsewhere. It therefore requires knowledge of physics, chemistry, biology, and many more specialized scientific areas including astronomy, geology, planetary science, microbiology, atmospheric science, and oceanography. However, astrobiology is more than just a collection of different disciplines. In seeking to understand the full story of life in the Universe in a holistic way, astrobiology asks questions that transcend all these individual scientific subjects. Astrobiological research potentially has much broader consequences than simply scientific discovery, as it includes questions that have been of great interest to human beings for millennia (e.g., are we alone?) and raises issues that could affect the way the human race views and conducts itself as a species (e.g., what are our ethical responsibilities to any life discovered beyond Earth?).
    Keywords: Exobiology
    Type: GSFC-E-DAA-TN40743 , Astrobiology (ISSN 1531-1074) (e-ISSN 1557-8070); 16; 8; 561-653
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  • 3
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    Evidence for only minor contributions from bacteria to sedimentary organic carbon (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Because their molecular signatures are often prominent in extracts of sediments, bacteria are thought to be important contributors to petroleum source beds. It has been shown recently, however, that abundances of biomarkers do not always reflect relative contributions to sedimentary organic carbon (Corg). The contribution of photosynthetic green sulphur bacteria to sediments can be assessed effectively because the diagenetic products of distinctive carotenoids from these organisms occur widely and their biomass is isotopically labelled, being enriched in 13C. We show here that, although sediments and oils from the Western Canada and Williston basins contain prominent biomarkers of photosynthetic bacteria, the absence of 13C enrichment in the total Corg requires that the bacterial contribution is in fact minimal. Although the importance of bacterial reworking of sedimentary debris cannot be doubted, we argue that our findings, when considered in conjunction with those from other settings, suggest that bacterial biomass may commonly represent only a minor component of total Corg in carbonaceous rocks.
    Keywords: Exobiology
    Type: Nature (ISSN 0028-0836); Volume 369; 224-7
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  • 4
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    Cleavage of an amide bond by a ribozyme (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A variant form of a group I ribozyme, optimized by in vitro evolution for its ability to catalyze magnesium-dependent phosphoester transfer reactions involving DNA substrates, also catalyzes the cleavage of an unactivated alkyl amide when that linkage is presented in the context of an oligodeoxynucleotide analog. Substrates containing an amide bond that joins either two DNA oligos, or a DNA oligo and a short peptide, are cleaved in a magnesium-dependent fashion to generate the expected products. The first-order rate constant, kcat, is 0.1 x 10(-5) min-1 to 1 x 10(-5) min-1 for the DNA-flanked substrates, which corresponds to a rate acceleration of more than 10(3) as compared with the uncatalyzed reaction.
    Keywords: Exobiology
    Type: Science (ISSN 0036-8075); Volume 267; 5195; 237-40
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  • 5
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    Molecular palaeontological evidence for food-web relationships (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors present evidence of organic compounds derived from insect waxes from sediments of the lagoonal and sabkha sedimentary systems of the coast of Abu Dhabi.
    Keywords: Exobiology
    Type: Die Naturwissenschaften (ISSN 0028-1042); Volume 81; 128-30
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  • 6
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    Ancient Aqueous Environments at Endeavour Crater, Mars (2014)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.
    Keywords: Exobiology
    Type: GSFC-E-DAA-TN21296 , Science (ISSN 0036-8075); 343; 6169; 1248097
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  • 7
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    XANES Analysis of Organic Residues Produced from the UV Irradiation of Astrophysical Ice Analogs (2011)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Organic residues formed in the laboratory from the ultraviolet (UV) photo-irradiation or ion bombardment of astrophysical ice analogs have been extensively studied for the last 15 years with a broad suite of techniques, including infrared (IR) and UV spectroscopies, as well as mass spectrometry. Analyses of these materials show that they consist of complex mixtures of organic compounds stable at room temperature, mostly soluble, that have not been fully characterized. However, the hydrolysis products of these residues have been partly identified using chromatography techniques, which indicate that they contain molecular precursors of prebiotic interest such as amino acids, nitrile-bearing compounds, and amphiphilic compounds. In this study, we present the first X-ray absorption near-edge structure (XANES) spectroscopy measurements of three organic residues made from the UV irradiation of ices having different starting compositions. XANES spectra confirm the presence of different chemical functions in these residues, and indicate that they are rich in nitrogenand oxygen-bearing species. These data can be compared with XANES measurements of extraterrestrial materials. Finally, this study also shows how soft X rays can alter the chemical composition of samples.
    Keywords: Exobiology
    Type: AD-A545869 , Advances in Space Research; 48; 6; 1126-1135
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  • 8
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    Wheat Crop in the Advanced Plant Habitat of the International Space Station (2018)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Plants are grown in the Science Carrier(SC)of the APH,(0.2m2instrumented)root module.
    Keywords: Exobiology
    Type: KSC-E-DAA-TN64236 , 2018 American Society of Agronomy Meeting; Nov 04, 2018 - Nov 07, 2018; Baltimore, MD; United States
    Format: application/pdf
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  • 9
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    Two-dimensional life? (1991)
    In:  Other Sources
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    Publication Date: 2019-08-17
    Description: A model [Wachtershauser, G. (1988) Microbiol. Rev. 52, 452-484], according to which life started in the form of a monomolecular layer of interacting anionic metabolites electrostatically bound to a positively charged surface, is examined critically. The model raises a number of thermodynamic and kinetic difficulties.
    Keywords: Exobiology
    Type: Proceedings of the National Academy of Sciences of the United States of America (ISSN 0027-8424); 88; 10014-7
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  • 10
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    Efficient transfer of information from hexitol nucleic acids to RNA during nonenzymatic oligomerization (1999)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Hexitol nucleic acids (HNAs) are DNA analogues that contain the standard nucleoside bases attached to a phosphorylated 1,5-anhydrohexitol backbone. We find that HNAs support efficient information transfer in nonensymatic template-directed reactions. HNA heterosequences appeared to be superior to the corresponding DNA heterosequences in facilitating synthesis of complementary oligonucleotides from nucleoside-5'-phosphoro-2-methyl imidazolides.
    Keywords: Exobiology
    Type: Journal of the American Chemical Society (ISSN 0002-7863); 121; 25; 5856-9
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