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Project Reports

• Project 1: The Origin of Homochirality

  Small biological molecules are frequently chiral, meaning that they can exist in both right-handed and left-handed forms. The two forms are identical except for the mirror symmetry that they break, and so would be expected to participate in chemical reactions in a way that does not depend on their chirality. When assembled into polymers, the resulting chains would therefore be expected to consist of a mixture of right and left-handed forms of the small molecules, a so-called racemic state. The surprise is that this is not true for the molecules of life. All chiral amino acids used by biology are left-handed and all chiral sugars are right-handed. That is, they are homochiral. This project is concerned with trying to find an explanation for this ubiquitous phenomenon, a universal aspect of all life on Earth. The specific question that is addressed is whether homochirality is a generic phenomenon of living systems, one that would be anticipated to arise if life were found elsewhere in the universe. Or is it instead some frozen accident related to the specific way that life arose on Earth? This question has been hotly debated in one form or other for over a hundred years, certainly since the time that Lord Kelvin coined the term “homochirality”. It is important for the Illinois NASA Astrobiology Institute for Universal Biology, because it is one of the two most evident universal phenomena of all life on Earth, the other being the universal genetic code. The phenomenon is important for another reason. The magnitude of the homochirality is 100%. It is not a slight imbalance in the abundance of right-handed vs. left-handed molecules. Thus, it is an unambiguous signal to measure, either from biological samples or remotely due to the effects of homochirality on the scattering of light waves. Specifically, homochiral solutions or suspensions will affect the polarization plane of electromagnetic waves, and so can readily be detected through optical means. The most exciting possibility in this regard is that if homochirality can be firmly established as a biological phenomenon, then its presence can be used as a biosignature of non-terrestrial life.

  ROADMAP OBJECTIVES: 1.2 3.2 3.4 4.1 4.2 7.1 7.2

• Inv 1 – Geochemical Reactor: Energy Production at Water-Rock Interfaces

  INV 1 examines water-rock interactions in the lab and in the field, to characterize the geochemical gradients that could be present at water-rock interfaces on Earth and other worlds, taking into account different ocean and crustal chemistries. We have fully investigated serpentinization as the most likely of all possible environments for life’s emergence on Earth as well as other water-rich worlds – a key goal for astrobiology as stated in the NASA Astrobiology Roadmap 2008. (Russell, 2015). Serpentinization is now recognized as fundamental to delivering the appropriate chemical disequilibria at the emergence of life. And the fact that this process is likely inevitable on any icy, wet and rocky planet makes its study fundamental to emergence of life, habitability and habitancy. Nevertheless, notwithstanding the thermodynamic drives to CO₂ reduction during the process, great uncertainty exists over just what kind of organic molecules (if any) are delivered to the submarine springs and consequential precipitate mounds. In attempts to clarify what these might be we have undertaken thermodynamic modelling and experimental investigations of the serpentinization process.

  ROADMAP OBJECTIVES: 2.2 3.1 3.2 3.3 3.4 4.1

• Modeling and Observation of Disks Project

  The broader goal of this NAI team is to understand and follow the evolution of complex, prebiotic organic molecules from the interstellar medium to their incorporation into planets. This Project’s work focuses on chemical evolution in the protoplanetary disk stage of planetary system formation. Disk matter provides the raw material for planet formation and its composition is thus expected to have a direct bearing on the composition of planets and eventually, the origin of life on them. We study disk chemical evolution via a two-pronged approach: (i) theoretical modeling of disk physical structure and its chemistry in time and the transport of matter in the disk as it evolves, and (ii) constructing synthetic line and continuum spectra and images of gas and dust in disks to compare with observational data from ground and space-based telescopes. New chemical networks that incorporate results from the Laboratory and Quantum Calculation Projects are developed and disk modeling results compared with observations to infer conditions under which the solar system and exoplanets formed.

  ROADMAP OBJECTIVES: 1.1 3.1 3.2

• Life Underground

  Our multi-disciplinary team from the University of Southern California, California Institute of Technology, Jet Propulsion Lab, Desert Research Institute, Rensselaer Polytechnic Institute, and Northwestern University is developing and employing field, laboratory, and modeling approaches aimed at detecting and characterizing microbial life in the subsurface—the intraterrestrials. We posit that if life exists, or ever existed, on Mars or other planetary body in our solar system, evidence thereof would most likely be found in the subsurface. This study takes advantage of unique opportunities to explore the subsurface ecosystems on Earth through boreholes, mine shafts, sediment coring, marine vents and seeps, and deeply-sourced springs. Access to the subsurface—both continental and marine—and broad characterization of the rocks, fluids, and microbial inhabitants is central to this study. Our focused research themes require subsurface samples for laboratory and in situ experiments. Specifically, we are carrying out in situ life detection, culturing and isolation of heretofore unknown intraterrestrial archaea and bacteria using numerous novel and traditional techniques, and incorporating new and existing data into regional and global metabolic energy models.

  ROADMAP OBJECTIVES: 2.1 2.2 3.1 3.2 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2

• Inv 2 – From Geochemistry to Biochemistry

  INV 2 focuses on experimentally simulating the geological disequilibrium in hydrothermal systems, and determining the role of minerals in harnessing these gradients toward the emergence of metabolism. Biology utilizes metals (to speed up reactions) and “engines” (such as electron bifurcators, to couple endergonic and exergonic reactions); these components in modern metabolism strongly resemble specific minerals found in hydrothermal environments. We focus on simulating these primordial geological components and processes that might have led to the beginning of metabolism in a seafloor system on a wet rocky planet.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 4.1 7.1

• Project 2: Cells as Engines and the Serpentinization Hypothesis for the Origin of Life

  All life is, and must be, “powered” since all of its most essential and distinguishing processes have to be driven “up-hill” against their natural thermodynamic direction. By the 2nd law of thermodynamics, however, a process can only be made to proceed up-hill by being mechanistically linked, via a molecular device functioning as an engine, to another, more powerful, process that is moving in its natural, down-hill direction. On fundamental principles, we argue, such engine-mediated conversion activities must also have been operating at, and indeed have been the cause of, life’s emergence. But what then were life’s birthing engines, what sources of power drove them, what did they need to produce, and how did they arise in an entirely lifeless world? Promising potential answers to these and other questions related to the emergence of life are provided by the Alkaline Hydrothermal Vent/serpentinization (“AHV”) hypothesis, whose original propounder and lead proponent, Dr. Michael Russell of JPL, is a co-investigator on this project. The goal of the project is specifically to clarify the essential mechanistic modus operandi of all molecular engines that power life, and to see how the most fundamental and prerequisite of these could have arisen, and operated, in the structures and flows produced by the serpentinization process. Importantly, candidate answers to these questions can be put to definitive laboratory tests.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 3.2 3.3 3.4

• Project 3: Theory for the Darwinian Transition

  One of the key puzzles of astrobiology concerns the precision, uniqueness and rapidity of early evolution. In order for life to have evolved the main components of the modern cell as early 3.8 billion years ago, with a unique genetic code that is virtually optimal in terms of minimizing translational errors, the mode of evolution would have had to be different from the current vertical transmission of genes. We had shown in 2006 that the collective mechanism of horizontal gene transfer (HGT) is the only one capable of solving the puzzle of early evolution. The HGT means that the evolutionary process before LUCA can be thought of as a network of interactions rather than a tree, as would be the case in vertical gene transfer. The multiple connectivity of the network accelerates the evolution and allows rapid convergence to a unique, near-optimal genetic code. With all these advantages of HGT, why would it ever stop? Our project uses computer simulation of digital organisms in order to address these generic questions about the exit of life from the collective, progenote phase to the current era of vertically dominated evolution.

  This project is potentially important for understanding biosignatures of life. Even on Earth, we are familiar with the tree-like structure of individual organismal lineages. If life were a network, as we believe that it once was, the usual phylogenetic pattern of individuality and species would not apply. If we encounter life on other planets, we cannot be sure if it will be in the collective (progenote) phase or the vertical-dominated phase. Thus it is interesting to understand better the inexorability and timing of the Darwinian Transition.

  ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 6.2

• Ancient Gene Families and HGT

  We have identified a subset of genes that appear to have been horizontally transferred from very ancient lineages that diverged earlier than the ancestor of the 3 known Domains of life.

  ROADMAP OBJECTIVES: 3.2 3.4

• Early Animals: Lipid Biosignatures

  We established the structures of two unusual steroid-related molecules that appear to be characteristic of Neoproterozoic ecosystems.

  We responded to an 2013 critique of the sponge biomarker hypothesis with a detailed rebutal. Currently, the most parsimonious interpretation of the presence of the unusual steroid, 24-isopropylcholestane, in Neoproterozoic sediments is that represents a molecular fossil of demosponges.

  We devolped a new approach to evaluating the diets of early hominins based on analyese of fecal sterols. We studied the fecal sterols of great apes and determined that they were distinct from the fecal sterols of Neandethals and modern humans (Sistiaga et al., 2015).

  ROADMAP OBJECTIVES: 3.2 4.2

• Project 4: Experiment on Darwinian Transition

  Carl Woese proposed that life started as semi-autonomous subcellular forms named progenotes. The progenotes lacked cell membranes and readily exchanged information, suggesting that aspects of information processing had already been developed. Woese further hypothesized that certain early life processes crossed a Darwinian threshold, where incorporation of new components of a processes was not tolerated. We aim at determining whether translation, transcription, and replication have crossed the Darwinian threshold. To determine whether DNA replication has crossed the Darwinian Threshold, interchangeability of the DNA replication processivity factor known as the sliding clamp is being examined. It is only in the presence of the sliding clamp that DNA polymerases in extant organisms can gain the speed required to replicate their genomes. In Bacteria, the sliding clamp is the -subunit of Pol-III and in Archaea and Eukarya the functional homolog is proliferating cell nuclear antigen (PCNA). We have, therefore, expressed and purified a sliding clamp from each of the three domains of life (E. coli -subunit, M. acetivorans PCNA, and human PCNA). Sliding clamps are loaded in a clamp loader dependent manner; therefore, we have cloned, expressed and purified an archaeal clamp loader from M. acetivorans. Our next step is to determine whether an archaeal clamp loader can interact with each of the sliding clamps from the three domains of life and whether any of the interactions leads to loading of the sliding clamps onto DNA to orchestrate processive DNA synthesis.

  ROADMAP OBJECTIVES: 3.2 3.4 4.2

• Project 1D: Comparative Genomic Analysis of Chemolithotrophic Fe(II)-Oxidizing Bacteria

  A comparative genomic analysis was performed to identify candidate genes involved in extracellular electron transfer (EET) by Fe(II)-oxidizing bacteria (FeOB). The analysis included a variety of publically-available FeOB genomes, together with genomes from FeOB isolated from subsurface sediments, previously-isolated marine basalt-associated FeOB, and metagenomes from chemolithoautotrophic aerobic pyrite-oxidizing and nitrate-reducing Fe(II)-oxidizing enrichment cultures. We identified outer membrane multi-copper oxidase (MCO) genes homologous to proteins known to be involved in EET in several of the FeOB genomes, as well as homologs to the outer membrane c-type cytochrome (ctyc) Cyc2 known to be involved in bacterial Fe(II) oxidation by Acidithiobacillus ferrooxidans under acidic conditions. Further, we found gene clusters that may potentially encode novel “porin-cytochrome-c protein complex” (PCC) in the well-known neutral-pH FeOB S. lithotrophicus ES-1, and homologous operons were found in other recognized FeOB (Leptothrix cholodnii SP-6 and Leptothrix ochracea L12. Another gene cluster consisting of a porin and three periplasmic multiheme cytc was identified in Hyphomicrobium sp. genome retrieved from a pyrite-oxidizing enrichment culture, and its homologous gene clusters are also present in five marine Zetaproteobacterial FeOB genomes. Overall, this analysis, which is based on our current understanding of bacterial EET in Fe redox reactions, provides a list of candidate genes for further experimental and genomic studies.

  ROADMAP OBJECTIVES: 2.1 3.2 4.1 5.1 5.3

• Exploring the Evolution of the Water and Organic Reservoirs in the Solar System

  This project investigates the evolution and stability of water and organic reservoirs in our Solar System, with particular emphasis on the characterization of the current and ancient habitability of planet Mars. We employ extremely powerful observatories (e.g., ALMA, Keck, VLT, future JWST) to acquire high spatial and spectral resolution maps of the isotopic and organic signatures on several bodies in the Solar System. These maps allow us to investigate the stability and evolution of their atmospheres, while localized plumes can be used to identify regions of active release. In this reporting period, we emphasized three areas:

  1. We advanced our pioneering work on characterizing the evolution of water on Mars, by developing a new observational plan that combines the power of ALMA, of Keck and of MAVEN to obtain maps of the water D/H signatures on Mars.

  2. We identified previously unknown chemical processes affecting singlet-O₂ and odd-oxygen on Mars, which may be indicative of a much more active photochemical cycle (with the possible intervention of heterogeneous processes).

  3. We provided science leadership in the investigation of Mars with the James Webb Space Telescope (JWST), and established a variety of observing modes and scientific opportunities.

  ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 4.1 7.1

• High Temperature W/R Hosted Microbial Ecosystems in Yellowstone

  Geochemical data indicate that life on early Earth was dependent on chemical forms of energy. This attribute, when coupled with phylogenetic data indicating that early evolving forms of life were thermophilic, lead many astrobiologists to believe that life evolved in a high temperature environment and was dependent on chemical forms of energy to sustain its metabolism.

  Hydrothermal environments with temperatures >70ᵒC exclude life dependent on light energy, leaving only those life forms that can sustain themselves using chemical energy. The >14,000 hot springs in Yellowstone National Park therefore provide a unique field-based early Earth analog environment to examine the processes that sustain life dependent on chemical energy and to investigate the metabolic processes that sustain this life. Moreover, the chemical and physical variation present in these environments affords the opportunity to examine how this variation drove the diversification of life in these early Earth analog environments. RPL investigations in hot spring environments in Yellowstone in 2015 centered on answering questions related to the array of energy and carbon sources available to chemosynthetic life, the preferred carbon sources supporting this life, and the role of hydrogen transformation in the metabolisms of these organisms. By answering these interrelated questions, we will provide a framework by which we can use to begin to understand the processes that most likely sustained microbial life on the early Earth. Since it is possible, if not likely, that such processes would also sustain early life on other planetary bodies, this research has the potential to guide the search for life in non-Earth environments.

  ROADMAP OBJECTIVES: 3.2 3.3 4.1 5.2 5.3 6.1

• Interstellar and Nebular Chemistry: Theory and Observations

  We continue to undertake theoretical and observational studies pertaining to the origin and evolution of organics in Planetary Systems, including the Solar System. In this performance period, we have focused on studies aimed at understanding the origin and processing of organics in the earliest evolutionary phases of stars like the Sun. These include formation pathways and related isotopic fractionation effects.

  We have continued observational programs designed to explore the chemical composition of comets and establishing their potential for delivering prebiotic organic materials and water to the young Earth and other planets. State-of-the-art international facilities are being employed to conduct multi-wavelength simultaneous studies of comets in order to gain more accurate abundances, distributions, temperatures, and other physical parameters of various cometary species. We are also leading an international collaboration to study the organic composition of Titan with the Atacama Large Millimeter Array (ALMA).

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 7.1 7.2

• Project 7: Mining Archaeal Genomes for Signatures of Early Life: Comparison of Metabolic Genes in Methanogens

  Methanogens represent the largest diversity among the archaea and have the unique ability to generate methane from simple compounds such as carbon dioxide, acetate and methylamines which were common in the anaerobic environments of early Earth and perhaps Mars. Methane biosynthesis also requires the presence/uptake of important ions such as sulfates, sulfides, carbonates, phosphates, and various light metal ions. In this project, we are attempting to analyze the evolution of the methanogens’ central cellular functions of translation, transcription, replication, and metabolism. To accomplish this, we are constructing the metabolic and regulatory networks of Methanosarcina acetivorans, the most complex methanogen known, and using these models to establish a framework for studying the evolution of methanogens. Results will be tested through microfluidic studies using varying carbon and ion sources.

  ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3 6.1 6.2 7.1

• Project 8: The Evolution of the Eukaryote-Archaea Common Ancestor

  The goals of our lab with respect to the NAI project are to describe early evolutionary via genomic and cellular comparisons of diverse eukaryotes to diverse archaea. We are interested in comparing genomes from diverse free-living eukaryotes to investigate the origins and evolution of eukaryotic complexity. Evolutionary reconstructions of early eukaryotes are challenged by a lack of sufficient taxonomic sampling. Few genomes of free-living microbial eukaryotes are sequenced, despite their critical importance in ecology, evolution, and basic cellular biology. The real challenge to protistan genomics is actually quite mundane; it concerns the lack of available and cultivatable free-living protists (mainly heterotrophs) in the laboratory. Yet, a better understanding of the genomic content diverse eukaryotes facilitates the evolutionary analysis of archaeal genomes. To address these issues of poor taxonomic sampling of eukaryotic genomes, my lab has developed a molecular method to separate eukaryotic DNA from bacterial DNA. We have demonstrated conclusively that we can separate eukaryotic chromatin from a mixture of eukaryotic and bacterial genomic DNA. This method will be widely applicable to the study of protistan genomics. Currently, our lab is in the process of assembling and annotating ten eukaryotic genomes from my lab’s culture collection of over 100 amoeboid protists from diverse phylogenetic groups. Many of these amoeba represent novel phyla-level lineages of eukaryotes.

  One amoebal genome is form is Nuclearia sp., which is an amoeboid protist closely and a member of a primary “supergroup” of eukaryotes – the Optisthokonts. This supergroup includes all animals, fungi, and several types of unicellular or colonial protists including choanoflagllates. Thus, genomic analyses of Nuclearia will inform the evolution of complexity and multicelllularity in both Fungi and Animals.

  ROADMAP OBJECTIVES: 3.2 3.4 4.2 6.2

• Advances in Gene Sequencing From Low-Biomass Water-Rock Hosted Ecosystems

  One of the approaches our team is taking to explore rock-powered life is to study microorganisms hosted within rocks that are undergoing potentially life-supporting reactions with water. The chemistry of the rock microenvironments shapes the abundance, diversity and distribution of microbial life. In turn, that microbial life locally affects the in-situ geochemistry. This project is currently focusing on the successful extraction and sequencing of the exceedingly small amounts of DNA that accumulates within rocks, in order to successfully detect and characterize the rock-hosted life. Ultimately our improved approaches will support the application of next-generation DNA sequencing technology in the study of natural microbial ecosystems that are key for understanding the mechanisms of rock-powered life.

  ROADMAP OBJECTIVES: 3.2 4.1 5.1 5.2 5.3 6.1 7.2

• Project 9: Metapopulation Structure

  Although often modeled as a single well mixed populations, microbes in terrestrial systems likely exist as metapopulations, isolated but connected by infrequent migration. This can change the evolution of complexity, increasing the effect of genetic drift and decreasing the effect of selection. It can increase diversity and the rate at which complexity evolves. We have argued that metapopulation structure may have existed in early life and been responsible for the rapid evolution of LUCA and diversification across the tree of life. We investigate microbial genome evolution in metapopulations in Yellowstone National Park. We find that indeed they represent evidence for both natural selection and genetic drift shaping these populations.

  ROADMAP OBJECTIVES: 3.2 3.4 4.2 6.2

• NAI ARC Communications

  The ARC NAI Team interacts with a number of institutions that fall outside the NAI proper. These include universities and other domestic and international organizations, chief of which are Langston University, the Chickasaw and Choctaw Nations, and the Dutch Astrochemistry Network, which is part of the Netherlands Organization for Scientific Research (NWO).

  ROADMAP OBJECTIVES: 3.1 3.2 3.4

• Rock Powered Life: Education and Communications

  The central theme of the Rock Powered Life research effort is to define how, where and when water/rock interactions release energy and how this energy is harvested to support microbial communities. These studies are of fundamental importance for improving understanding of how microbial life was supported on early Earth. Moreover, since similar reactions can be expected on any rocky planet with liquid water, these studies provide new constraints for predicting the distribution of life on other planetary bodies.

  The focus of our team – rock-hosted microbial ecosystems that are dependent on chemical rather than light energy – provides novel avenues to engage the next generation of astrobiologists and to disseminate knowledge to the broader public. Here we describe current and ongoing efforts by members of Rock Powered Life that are aimed at improving engagement and training in astrobiology. Of particular relevance are efforts to provide opportunities to provide underrepresented high school and undergraduate students hands on training opportnities in astrobiology-focused studies. We also describe advancements in Rock Powered Life’s digital-based information sharing technologies. Through these integrated team efforts we aim to attract and train future generations of astrobiologists and to provide greater access to the current knowledge base with which to understand the potential for life elsewhere on other planetary bodies.

  ROADMAP OBJECTIVES: 3.2 4.1 4.2 5.1 5.2 5.3 6.1 6.2

• The Long Wavelength Limit of Oxygenic Photosynthesis

  Oxygenic photosynthesis (OP) produces the strongest known biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. The pigment chlorophyll a was long considered the unique controller of both of these biosignatures, in its capability to enable water splitting to obtain electrons and thus produce oxygen as a biogenic gas, through spectral absorbance of light from the blue to 680 nm in the red. Then the discovery in 1996 of the cyanobacterium Acaryochloris marina shattered this conventional wisdom. A. marina was found to have replaced 93-97% of Chl a with Chl d, which enables it to perform oxygenic photosynthesis with much lower energy photons in the far-red/near-infrared. Since that first discovery in 1996, more far-red oxygenic phototrophs have been discovered, revealing a previously unsuspected diversity in the photosystems of oxygenic phototrophs. We seek to determine the long wavelength limit at which OP might remain viable and what factors affect the selection of that wavelength limit. This would clarify whether and how to look for OP adapted to the light from stars with a difference radiance spectrum from our Sun.

  Under this project in previous years and with other co-investigators, we spectrally quantified the thermodynamic efficiency of photon energy use in Acaryochloris marina str. MBIC11017, determined that its water-splitting wavelength is in the range 710-723 nm, and that it is more efficient than a Chl a cyanobacterium. The current focus of the project is to understand the adaptations of far-red/near-infrared (NIR) oxygenic photosynthetic organisms in general: in which environments they are competitive against chlorophyll a organisms, and what energetic shifts have been made in their photosynthetic reactions centers to enable their use of far-red/NIR photons. We are conducting field sampling and measurements to isolate new strains of far-red-utilizing oxygenic photosynthetic organisms, to quantify the spectral and temporal light regime in which they (and previously discovered strains) live in nature, and to use these light measurements to drive kinetic models of photon energy use to determine efficiency thresholds of survival.

  ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2

• Serial Measurements of the Volatile Composition of Comet D/2012 S1 (ISON) between 1.2 and 0.34 AU from the Sun

  The composition of ices and rocky material in cometary nuclei is central to understanding their origins, and to assessing their possible roles in delivering water and prebiotic organic compounds to the young Earth. For most comets, measurements of primary volatiles (ices contained in the cometary nucleus) exist for only a single date or for very few dates, questioning whether such ‘momentary’ measurements represent the bulk content of the nucleus. The early discovery of the dynamically new, sun-grazing comet C/2012 S1 (ISON) was extremely rare in that it permitted measurements of the abundances of sublimed ices over a large range of heliocentric distance (R_h). As part of a world-wide observing campaign, world-class astronomical observatories provided large amounts of observing time dedicated to studying Comet ISON. Using high-resolution infrared spectroscopy at Keck-2 and the NASA-IRTF, the GCA Team measured production rates for H₂O and eight trace gases (CO, C₂H₆, CH₄, CH₃OH, NH₃, H₂CO, HCN, C₂H₂) on ten pre-perihelion dates that spanned heliocentric distances ranging from 1.21 to 0.34 AU. This project addressed the evolution in molecular production and composition as the comet approached the Sun. GCA members also investigated the spatial distribution of H₂O in the near-nucleus coma to identify modes of water release and of heat injection by release from icy grains, and they conducted a sensitive search for HDO to test the potential delivery of Earth’s oceans by such comets.

  ROADMAP OBJECTIVES: 3.1 3.2

• Laboratory Studies

  The Laboratory Studies project uses a variety of cryo-vacuum systems to study the physical and chemical properties of astrophysically relevant materials to better understand the extent to which these materials can be converted in more complex organic materials of astrophysical and astrobiological importance. We concentrate on mimicking conditions found in astrophysically relevant environments involving low temperatures, low pressures, and high radiation fields. The main processes we explore are the photolytic processing of mixed molecular ices and organics and chemistry that occurs at gas-solid interfaces.

  ROADMAP OBJECTIVES: 3.1 3.2 3.4

• Computational Quantum Chemistry

  We investigated the formation and functionalization of nitrogen substituted cyclic aromatic molecules such as the precursors of biomolecules, polycyclic aromatic hydrocarbons, and the feasibility of their detection via spectroscopic techniques.

  ROADMAP OBJECTIVES: 3.2

• Physiology of Microbial Populations From W/R Hosted Ecosystems

  Microbial communities supported by chemical energy (chemotrophic communties) released through water / rock interactions are widespread in contemporary Earth environments, including the subsurface where light is excluded and in surface environments where physical or chemical conditions preclude photosynthetic metabolisms. Chemotrophic microorganisms are key targets of astrobiological investigation due to the strong likelihood that they predate photosynthetic metabolisms and because they can be physiologically tested to define the habitable limits for life on Earth, including those associated with extremes of temperature, pH, salinity, and energy availability. Research by RPL scientists is focused on identifying and characterizing the physiological strategies or mechanisms that allow life to persist under extreme conditions at the habitable limits. By combining this information with phylogenetic approaches, we aim to determine how and when these mechanisms evolved and what role they played in the diversification of early life. As such, this research effort is highly interdisciplinary and employs both traditional (e.g., activity assays, cultivation) and contemporary (genomics, transcriptomics, metabolomics) microbiological approaches in combination with geochemical approaches. In addition, RPL investigators are studying the evolution of these communities to hone in on the nature of key physiological processes (e.g., central carbon metabolism, nitrogen metabolism, and iron-sulfur metabolism) in chemotrophs prior to the onset of photosynthetic metabolisms. Field-based RPL investigations of microbial physiology in water/rock ecosystems to date have focused on populations inhabiting subglacial environments (cold-adaptation), hot springs (adaptation to acidity, high temperature), and subsurface peridotite environments (adapation to energy stress, nutrient stress, alkalinity).

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 4.1 5.1 5.2 5.3

• Progress in the Elucidation of Microbial Biosignatures

  A number of discrete individual investigations have contributed to improved knowledge about the occurrence and interpretation of microbial molecular biosignatures across all geological timescales.

  A new analytical approach enabled a revised geologic distributions of fossilized biomarkers for anoxygenic sulfur bacteria. The prevalence of okenane and chlorobactane suggests that marine photic zone euxinia (PZE) was more intense and frequent in the geologic past. However, the presence of these compounds in some sediments and oils may also be a signature for basin restriction rather than one indicating more widespread marine anoxia.

  In a related work, pervasive photic zone euxinia and disruption of biogeochemical cycles was demonstrated for a sequence of rocks deposited on the northeastern Panthalassic Ocean during the end-Triassic extinction.

  A study of lipids and their isotopic compositions, combined with stable isotope probing experiments, demonstrated that streamer biofilm communities, which are a present in the high temperature zones of hydrothermal features of the Lower Geyser Basin of Yelowstone National Park, can alternate their metabolism between autotrophy and heterotrophy depending on substrate availability.

  Other collaborations with numerous colleagues resulted in documentation of lipid and isotopic biosignatures in cultured bacteria.

  ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.2 5.3 6.1