AbstractsAstrobiology Graduate Conference (AbGradCon) 2011HOSTED BYMontana State UniversityBozeman, Montana • June 5–8, 2011

Abstract

AstrobiologyVol. 11, No. 4 Free AccessAbstractsAstrobiology Graduate Conference (AbGradCon) 2011HOSTED BYMontana State UniversityBozeman, Montana • June 5–8, 2011Published Online:20 May 2011https://doi.org/10.1089/ast.2011.1400AboutSectionsPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail AbGradCon 2011 Oral PresentationsJosé C. Aponte Brown University, Providence, RI, USAAGC11-t01 Evidence for the Homogeneity of Abiotically Synthesized Organic Matter in the Solar SystemBecause carbonaceous chondrites (CCs) represent some of the oldest and most primitive materials in the Solar System, their organic matter content can be used to decipher the history of prebiotic organic chemistry and how it may have resulted in the development of life on Earth. Many families of organics have been identified in CCs, among them; monocarboxylic acids (MCAs) are of particular astrobiological importance due to their high abundance, and their potential role on the evolution of the lipid bilayer of the cell membrane. MCAs can be found in their free form or derived from insoluble organic matter (IOM) in CCs using RuO4 oxidation. The content and distribution of free MCAs can be greatly affected by secondary thermal and aqueous alterations on the parent bodies. IOM-derived MCAs, in contrast, may be far more resistant to these secondary alterations. To better understand the impact of secondary alterations on the composition of MCAs and IOM, we determined the distributions and isotopic ratios of free and IOM-derived MCAs in six carbonaceous chondrites with very different secondary alteration processes. We found that free MCAs show dramatically different distributions in different samples, however; IOM-derived MCAs are very similar regardless of the degree of thermal and aqueous alterations. Our data suggest that aliphatic structures are well preserved in IOM despite of the major secondary alterations. The high degree of similarity in IOM-derived MCAs suggest a common origin of abiotic organic matter throughout the Solar System.Dimitra Atri University of Kansas, Lawrence, KS, USAAGC11-t02 Extragalactic Cosmic Rays and Terrestrial Biodiversity CyclesA ∼ 62 My periodicity in terrestrial biodiversity has been observed in independent studies of paleobiology databases going back to 500 My. The period and phase of this biodiversity cycle correlates with the motion of our solar system in the galactic disk that oscillates perpendicular to the galactic plane with an amplitude of about 70 parsecs and a period of 63.6 My. Our Galaxy is falling toward the Virgo cluster due to its gravitational pull, forming a galactic shock at the north end of our galaxy due to this motion, capable of accelerating particles and exposing our galaxy's northern side to a higher flux of cosmic rays. These high-energy particles strike the Earth's atmosphere initiating an extensive air shower, ionizing the atmosphere by producing charged secondary particles. Increased ionization leads to changes in atmospheric chemistry, resulting in ozone depletion, which increases the flux of solar UVB radiation at the surface and is potentially harmful to living organisms. Secondary particles such as muons produced as a result of nuclear interactions are able to reach the ground, enhancing the biological radiation dose, causing DNA damage and increasing mutation rates, which can have serious biological implications for terrestrial and subterrestrial life. Using a Monte Carlo simulation package CORSIKA, we quantify these effects resulting from enhanced cosmic ray exposure and discuss their impact on the Earth's atmosphere and terrestrial biodiversity.Armando Azúa-Bustos Pontificia Universidad Católica de Chile, Santiago, ChileAGC11-t03 Chroococcidiopsis atacamensis, a New Hypolithic Cyanobacteria Isolated from the Hyperarid Atacama DesertThe Atacama Desert is the driest place on Earth, with an arid core highly adverse to the development of life. Here, we report that along the coast in these arid regions, complex associations of cyanobacteria, archaea, and heterotrophic bacteria inhabit the undersides of translucent quartz stones. Colonization rates in these areas, which receive virtually no rain but mainly fog, are significantly higher than those reported inland in the hyperarid zone at the same latitude. This finding strongly suggests that hypolithic microbial communities thriving in the seaward face of the Coastal Range can survive with fog as the main regular source of moisture. A model is advanced where the development of the hypolithic communities under quartz stones relies on a positive feedback between fog availability and the higher thermal conductivity of the quartz rocks, which results in lower daytime temperatures at the quartz–soil interface microenvironment. From this site, we were able to culture several species of cyanobacteria, one of which we identified as a new species of the Chroococcidiopis genus, highly tolerant to low water availability. This tolerance seems to be explained, in part, due to the production of high amounts of sucrose that work as an intracellular compatible solute that helps to maintain cell ultrastructure under these stressful conditions.Anja Bauermeister Institute of Aerospace Medicine, Cologne, GermanyAGC11-t04 Acidophilic Iron-Sulfur Bacteria and Their Relevance for MarsDuring the last few decades, orbiter and lander missions to Mars have revealed extensive regions of layered deposits, composed of ferric oxides and sulfate minerals. These sediments indicate the possible existence of an aqueous, acidic environment in parts of early Mars. Bacteria similar to chemolithoautotrophs on Earth, known to strive in acidic, iron- and sulfur-rich environments, could have been an integral part of a potential extinct martian ecosystem, and might possibly even exist today in protected subsurface niches. Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans were chosen as model organisms to study the ability of iron-sulfur bacteria to survive or grow under simulated martian subsurface conditions. Different viability markers are used to give a more comprehensive view on bacterial activity and death. Both microbes can utilize a variety of electron donors and acceptors for energy-generating redox reactions, and are facultative anaerobes. They are also able to grow on mixtures of Mars analog regolith, composed of Mars-relevant iron-sulfur-minerals, without additional nutrients. Their resistance to single stress factors such as desiccation, high salt concentrations, low pressure, UV and ionizing radiation, and low temperatures is investigated. Both organisms are sensitive to short-term desiccation, and the presence of minerals does not exhibit any protective effect. However, when grown as a biofilm, the bacteria are able to survive longer periods of drying. Ongoing experiments aim to adapt the bacteria to Mars-like conditions and expose them to combined stressors in a Mars simulation chamber, creating a subsurface environment.Trevor Beard Montana State University, Bozeman MT, USAAGC11-t05 An Evaluation of the Inefficiency Objection in Origin of Life Theories: A Lesson from Simpson's ParadoxThe “inefficiency objection” states that the reactions proposed by competing origins of life theories are both too inefficient and not specific enough to explain the generation of early life. We use the Simpson's paradox (SP) as a tool for challenging this objection. We argue that on primitive earth, reactions could be inefficient locally, yet they could be simultaneously efficient as a whole, leading to life's emergence.SP involves the reversal of the direction of a comparison when data from several individual groups are combined to form a global whole. In molecular dynamic cases of SP, we observe, over a period of time, the reversal of which molecular product evolves to become the major product globally when sub-reactions are pooled together. Take each sub-reaction of the reverse TCA, the functional molecules, citric acid, grow at a slower rate than the non-functional molecules, succinic and glyoxylic acids, an inefficient reaction. With the help of SP, we, however, show that although functional molecules grow less rapidly than the non-functional ones in many sub-reactions, the functional molecules can emerge as the major products globally. This indicates that the production of reduced carbon and functional RNA from prebiotic precursors can be far more chemically plausible globally than indicated by RNA world, or metabolism first theories' detractors. If a reaction can be efficient globally as shown by SP, then the inefficiency objection to the origin of life theories is untenable, thus the emergence of life on early Earth seems more probable than ever before.Paul Black University of Rochester, Rochester, NY, USAAGC11-t06 Conjecture on the Possibility that the Highly Selective Response of DNA to Ionizing Radiation Was an Evolutionary Force in the Origin of Life?Life originating around 4 Ga was exposed to high fluxes of ionizing radiation. Ionizing radiation creates damage by two distinct mechanisms: (i) the indirect effect is by energy absorption in the water, creating reactive water radicals that attack biomolecules, and (ii) the direct effect is by energy absorption in the biomolecule itself. In mammalian cells, the direct and indirect effects are approximately of equal importance. This talk will focus on damage produced in nucleic acids by the direct effect. Damage to DNA by the direct effect is surprisingly selective. Ionization creates an electron-loss site (called a radical cation or hole) and an electron-gain site (called a radical anion or reduced site). From pulse radiolysis, EPR spectroscopy, and product analysis, quite a bit is known with regard to the initial distribution of holes and reduced sites and the final products stemming from these initial radicals. One-electron reduction is exclusively at Cyt and Thy, with initial electron capture by Cyt being ∼10 × greater than Thy. Holes are preferentially trapped by Gua, Ade, and deoxyribose, with approximate ratios of 10:1:5, respectively. Therefore, damage is highly selective for CG and exceeds damage to deoxyribose by ∼4 fold. In regards to backbone damage, the ribose of RNA is significantly more susceptible to hydroxyl attack than is the deoxyribose of DNA. Conjecture is given on how the differences between the radiation responses of RNA vs. DNA would drive the evolution of an RNA world into a DNA world.Mark Booth Herzberg Institute of Astrophysics, Victoria, BC, CanadaAGC11-t07 Constraining the Number of Habitable Planets Using Debris DiscsA decade before the discovery of the first extrasolar planet came the discovery of debris discs. Debris discs are discs of dust and planetesimals similar to the asteroid and Kuiper belts in our own Solar Systems. The properties of these discs can be used to provide us with information about the planetary systems they inhabit. Locations of the dust and structure in the disc can tell us about interactions between the disc and planets both past and present. Information on the disc can also tell us about the level of cometary bombardment any habitable planets may be receiving. It is thought that the inner Solar System went through a period known as the Late Heavy Bombardment (LHB) about 800 Myr after its formation caused by the migration of the giant planets. I present models of the observable properties of the Solar System throughout its history, showing the effect of the LHB on the debris disc, and compare these with the statistics of observed debris discs. I find that events like the LHB are rare, occurring around less than 12% of Sun-like stars. I then show results of simulations of dynamical instabilities, showing the connection between cold debris discs and the presence of habitable planets. I show that our modeling predicts that approximately 60% of Sun-like stars should have terrestrial planets. I conclude by discussing the implications for the number of habitable planets and the fraction of these systems likely to have life.Nicholas Boswell Montana State University, Bozeman, MT, USAAGC11-t08 The Positive Cooperation of a GTPase and an Fe-S Protein: The Interaction of Two Functions Likely Present During AbiogenesisHydrogen metabolism, as evidenced by its presence in a wide array of organisms from diverse evolutionary backgrounds, was likely an important process present at the origin of life and a key component to early life. One of the enzymes that reversibly reduces protons to dihydrogen, [FeFe]-hydrogenase, has a complex metallocofactor that consists of an Fe-S cluster with biologically unusual ligands carbon monoxide and cyanide, as well as a dithiolate linker. This complex metal cluster, termed the H-cluster, is biologically synthesized by two Fe-S containing radical S-adenosylmethionine (SAM) enzymes and one Fe-S containing GTPase. The P-loop motif responsible for coordination of nucleotide triphosphates like GTP is believed to be one of the most ancient markers of early biological catalysts. Additionally, non-biological and protobiological Fe-S clusters were likely important in catalyzing small molecule interconversion reactions (such as hydrogen oxidation and reduction reactions) during the transition period from abiotic to biotic processes. We have recently shown a positive interaction exists between the radical SAM enzyme HydE and the Fe-S containing GTPase HydF during H-cluster maturation. HydE and HydG both increase the GTPase activity of HydF by 50%, indicating a role for GTP hydrolysis in forming the H-cluster precursor and providing a link between Fe-S systems and P-loop nucleotide triphosphate systems. Despite the fact that the modern enzymes have undergone extensive evolutionary refinement, the H-cluster biosynthetic pathway provides an excellent experimental model to probe the potential coupling of Fe-S catalysis and GTP binding and hydrolysis for the processes associated with a burgeoning biotic world.Aditya Chopra The Australian National University, Acton, AustraliaAGC11-t09 Do the Elements Support a Hydrothermal Origin of Life?A number of genomic and proteomic features of life on Earth, like the 16S ribosomal RNA gene, have been recognised as being conserved over billions of years. Genetic and proteomic conservation translates to conservation of metabolic pathways to varying degrees across taxa. It follows that the stoichiometry of elements that make up the cellular components will be conserved to varying degrees across taxa.Based on the similarities in the elemental composition of Eukarya (as represented by humans) and Bacteria, we suggest that the stoichiometry of life, i.e. its bulk elemental composition, is a conserved feature of life on Earth. This allows us to infer the elemental composition of the Last Universal Common Ancestor (LUCA). Since, the elemental composition of an organism will also reflect to some extent the elemental abundances in its environment; we suggest that the inferred stoichiometry of LUCA could be used as a proxy for the stoichiometry of its environment.I will present elemental abundances in the fluids around different types of hydrothermal vents and compare it to the inferred abundances in LUCA. The results could enable us to exclude certain hypothesised sites for the origin of life such as surface ocean waters but also help us identify modern analogues of geological sites such as hydrothermal vents where LUCA may have existed and where life first evolved from its prebiotic origins.Callie Cole University of Colorado, Boulder, CO, USAAGC11-t10 Reactions of H Atoms with Anionic Carbon-Nitrogen Species in the Gas PhaseA fundamental goal of astrobiology is to discover the origin of life in the universe. An intimate knowledge of the chemical reactions taking place in the interstellar medium (ISM) may contribute more pieces to this complex puzzle. Reactions involving organic molecules are especially important to astrobiology. Several carbon- and nitrogen-containing anions have been spectroscopically detected in the ISM, and this study focuses on their gas phase reactivity with the most abundant interstellar species, hydrogen atom. The tandem flowing afterglow-selected ion flow tube (FA-SIFT) was used to experimentally determine the rate constants, products, and branching ratios of these reactions. CnN− (n = 1-6), (n = 1, 3, 4, 5), and (n = 2, 4) were formed by cold-cathode discharge from a graphite rod in the presence of N2, and were thermalized in helium buffer gas. Reagent ions were then mass-selected using a quadrupole mass filter before entering the reaction flow tube. Hydrogen atoms were formed by the thermal dissociation of H2, and subsequently introduced into the flow tube. A second quadrupole mass filter coupled to an electron multiplier was used to detect the reaction products. Theoretical calculations at the B3LYP/aug-cc-pVTZ level were conducted to further understand the mechanisms of these reactions. In future studies, larger biologically relevant molecules including amino acids will also be studied in the context of their reactivity with hydrogen atom. Overall, an exploration of interstellar reactions is integral to answering one of the principal questions raised by astrobiology: the origin of life in the universe.Kathleen L. Craft Virginia Tech, Blacksburg, VA, USAAGC11-t11 Models of Martian Hydrothermal Circulation, Ice Melt and Basalt AlterationWith physical processes similar to terrestrial seafloor hydrothermal systems, martian hydrothermal systems may provide a mechanism for transporting water, chemicals, and energy to the surface. These systems could shape surface morphology and may provide favorable environments for biological processes. Here we model a sill intrusion beneath a layer of basaltic rock and ice and investigate the melting process, induced fluid circulation and resulting rock alteration minerals. These models improve upon previous investigations by considering heat transfer through both conduction and convection. Results indicate fluid flow rates at ∼0.1 km3/yr for a 1 km2 sill surface area. This flow rate is much lower than those estimated for forming surface features; however, the melt water could be stored until the ice layer melts through and releases a large volume of fluid over a short time.Hydrothermal rock alterations within the melt layer are also investigated. The model suggests that higher temperature alteration minerals such as chlorite, actinolite, and epidote would tend to form first at depth, whereas low temperature zeolites and clay minerals would form near the top of the ice melt zone. With increasing time, convection within the melt layer will cause the temperature to decrease and the low temperature alteration products will overprint or replace the high-temperature alteration minerals. Observation of these altered mineral layers would be evidence of hydrothermal activity and may also indicate ideal locations to search for evidence of life on Mars.Julia DeMarines International Space University, Strasbourg, Alsace, FranceAGC11-t12 Social Implications of AstrobiologySince the first detection of an extrasolar planet in 1992, Astronomers have discovered over 529 extrasolar planets, and this number will most certainly be outdated by the time you read this sentence. Before knowledge of extrasolar planets became a common place in society the average person was not subjected to facts of other solar systems, or even other earths. Thanks to the advancement of extrasolar planet detection technologies the discovery of Earth-like planets will surely be a common place in the media in the upcoming decades. In turn, the idea of life on other planets will become more realistic and less science fiction, even more so as advancements are made in the spectral analysis of exoplanetary atmospheres and surfaces. In the event that extraterrestrial life is detected, a wide range of human social groups will be affected including the views and cultures, generations and religions. I will examine the sociology of Astrobiology, focusing on the search for extraterrestrial life (both primitive and intelligent) and its social implications (from the microscopic to the macroscopic level of agency) as well as the ethics of messaging to extra-terrestrials. I will also include a small case study examining the views of an international group (representing 25 nationalities) of roughly 60 Millennial generation (generation X and Y) students of how their belief system will be affected in the case of life detection.Geoffrey Diemer Portland State University, Portland, OR, USAAGC11-t13 Astrobiology: Virus Evolution and BiogeographyViruses are simple, yet highly evolved and efficient biological organisms. Molecular virology provides a means of understanding the persistence and evolution of rudimentary replicative systems and may thus provide insights into the characteristics of proto-life. Although viruses are known to be the most abundant organisms on Earth, their collective evolutionary history, biodiversity, and functional capacity are not well understood. Therefore, we are investigating virus diversity in Boiling Springs Lake (BSL): a large, acidic hotspring (pH 2.5, 55–95°C) located in Lassen Volcanic National Park, USA, which supports a relatively simple microbial ecosystem comprised of Archaea, Bacteria and several species of unicellular Eukarya. To identify viruses in BSL we extracted and sequenced DNA from virus-sized particles (<0.2 μm) isolated from 20 liters of BSL sediment. The vast majority of the ca. 380,000 sequences obtained do not match any characterized sequence in the public databases, and only 0.6% are identifiable as viral. Three Microvirus genomes have been fully reconstructed from a small subset of the viral sequences. Microviruses are among the simplest viruses known and are all remarkably similar despite their broad diversity and global distribution. Consequently, we have been able to investigate specific viral adaptations in response to local extremes of the BSL environment, and demonstrate phylogenetic relationships amongst BSL and other Microviruses. To discover completely novel viruses and address global virus biodiversity, we are attempting to determine whether the unidentifiable sequences denote common, yet uncharacterized environmental viruses, or whether they are derived from viruses unique to BSL.Shawn D. Domagal-Goldman and Katherine E. Wright NASA Headquarters; University of Colorado at BoulderAGC11-t14 The Astrobiology Primer v2.0: An Early-Career Astrobiology ProjectThe Astrobiology Primer is an introductory text, designed to give newcomers to the field a brief, but comprehensive, introduction to astrobiology that is longer than a review paper but shorter than a textbook. The primer grew out of the AbGradCon community, and like AbGradCon, it is a project conceived and run by and for early-career astrobiologists (graduate students and post-doctoral scientists). The original primer was published in 2006 in Astrobiology and was widely welcomed. The two of us are the Co-Lead Editors of the second edition. We are updating the primer to take account of new developments, and we are also completely re-writing the text using a more holistic approach. Our main goal is to produce something that is useful to other early-career astrobiologists, but we hope it will also be used more widely in education and outreach. It will be freely available to all online. We hope the primer will not only be useful, but will also be fun to read, and that it will convey our excitement and enthusiasm for astrobiology. An added benefit is that the process of writing the primer is, in itself, a way to strengthen the international early-career astrobiologist network as our team of volunteers covers 11 different countries in Europe, North America, South America, and Australia. At AbGradCon, we will discuss the community's progress on the primer, and preview its content and plans for publication.Benjamin Duffus Montana State University, Bozeman, MT, USAAGC11-t15 Astrobiological Implications of the Radical AdoMet Enzyme HydG in Promoting Organic Proto- Biomolecule Diversity in the Prebiotic to Biotic Transition on the Early EarthIron-sulfur (Fe-S) clusters in enzymes can be viewed as highly tuned mineral catalysts that may provide insight into catalysis central to the prebiotic to biotic transition on the early Earth. By understanding the chemical reactions of Fe-S cluster catalysts in biological systems, structural determinants in the transition between these stages can be postulated. As a model system, [FeFe]-hydrogenases perform the catalytic reduction of protons to dihydrogen at the catalytic “H-cluster,” a highly tuned organometallic cluster containing iron and sulfide as well as carbon monoxide, cyanide, and a nonprotein dithiolate ligand. Biosynthesis of this cofactor requires a scaffolding protein (with a GTP-binding domain) as well as two radical S-adenosylmethionine (AdoMet) enzymes. Recently, we have shown that the radical AdoMet enzyme HydG catalyzes cyanide and carbon monoxide ligand formation from the decomposition of an amino acid at an Fe-S cluster. Together, these results provide a basis for understanding the diverse reactivity of iron-sulfur clusters and radicals, reactivity that may have been important in the prebiotic conditions on the early Earth. More specifically, this work provides insights into the potential for prebiotic Fe-S/radical chemistry to catalyze the modification of Fe-S minerals to produce new catalytic activities that may have been involved in the initial conversion of atmospheric gases required for the emergence of life.Ian S. Foster University of California, Los Angeles, CA, USAAGC11-t16 Microbial Permineralization in Phanerozoic Gypsum Deposits: High Potential Target Rocks for Astrobiology ObjectivesThe search for an extant and/or ancient martian biosphere relies heavily on the selection of environments and mission sites that are likely to preserve indications of life. The focus of site selection for future missions has recently shifted towards phyllosilicates and away from sulfates as target rocks, despite the presence of large sulfate deposits at the martian surface. It is widely assumed that sulfates, much like carbonates, do not preserve microorganisms within crystals during growth and are therefore not desirable target minerals for future study. However, our current work, which focuses specifically on gypsum deposits, has demonstrated that gypsum crystals both trap and preserve microorganisms during growth, and commonly do so in a manner that results in the preservation of large microbial populations. Samples from various geologic ages and locations have been examined including: Permian (∼300 Ma) samples from the Delaware Basin, Texas; Miocene samples (∼7 Ma) from the Vena del Guesso Formation, Italy; and modern gypsum crystals from hypersaline environments in Australia, Baja, and Peru. All ancient samples contain demonstrably permineralized microorganisms, whereas modern samples illuminate a common mechanism of preservation and provide a potentially useful tool for determining both the rate of crystal growth and the paleo ‘up’ direction of such deposits. The markedly high frequency of preservation observed in terrestrial examples, combined with the potential ease of obtaining gypsum samples on Mars, since they are surficial deposits, strongly suggests that gypsum should be reconsidered as a high priority target rock for future martian astrobiology studies.Greg Fournier Massachusetts Institute of Technology, Somerville, MA, USAAGC11-t17 Ancestral Reconstruction of Synthetase Paralogs: Inferring Ancient Events in Genetic Code EvolutionAminoacyl-tRNA synthetase (aaRS) protein families specific for each amino acid diverged early in life's history, before the time of the Last Universal Common Ancestor (LUCA), around 4 billion years ago. The co-evolutionary model of the genetic code suggests that these divergences either added new amino acids (neofunctionalization) or increased specificity between very similar amino acids (subfunctionalization). Each of these hypotheses can be tested using ancestral sequence reconstructions from existing genomic data, as neofunctionalization predicts that one cognate amino acid will be absent within the sequence of reconstructed pre-LUCA paralog ancestors, while subfunctionalization predicts the ancestor will contain an overabundance of sites with ambiguous likelihood for either cognate amino acid. Homogeneous and nonhomogeneous ancestral reconstructions were performed on alignments of tyrosyl-tRNA (TyrRS) and tryptophanyl-tRNA (TrpRS) synthetase protein sequences from 112 species, as well as 100 sets of simulated sequences. Amino acid usage rates, joint probabilities, and the degree of ambiguity between cognate amino acid pairs were all subsequently calculated from the probabilistic reconstructions. The reconstructed paralog ancestor of TyrRS and TrpRS contains no Trp, with a low joint probability (14.8%), a significant result supported by simulation studies. In contrast, analysis of aliphatic amino acids (Ile, Val, Leu) shows that sites reconstructing to either Ile or Val grow increasingly ambiguous approaching the pre-LUCA paralog ancestor (65% ambiguous, vs. 23% in domain ancestors). These results provide novel, compelling empirical evidence in support of the co-evolutionary model of genetic code, which is shown to include both neofunctionalization and subfunctionalization events.Aaron Goldman Princeton University, Princeton, NJ, USAAGC11-t18 The TIM Barrel Fold, Early Life Forms, and the Nature of Biological ComplexityThe triosephosphate isomerase (TIM) barrel protein fold is thought to be present in a whopping 10% of all modern enzymes. T