2014 Annual Science Report

Astrobiology Roadmap Objective 5.2 Reports Reporting  |  SEP 2013 – DEC 2014

Project Reports

  • Life Underground

    Our multi-disciplinary team from USC, Caltech, JPL, DRI, RPI, and now also Northwestern 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 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2
  • Biosphere-Geosphere Stability and the Evolution of Complex Life

    Both the rise of complex life and the Phanerozoic mass extinctions are accompanied by significant perturbations of the carbon cycle. Attention is usually focused on causality, and environmental change is almost always considered the driver. Yet the co-evolution of life and the environment suggests that the fundamental issue is not causality but rather stability. This project seeks to develop a theory of biosphere-geosphere stability and to test it using the geochemical and fossil records.

    ROADMAP OBJECTIVES: 4.2 4.3 5.2 6.1
  • Astrobiology of Icy Worlds

    Our goal in the Astrobiology of the Icy Worlds Investigation is to advance our understanding of the role of ice in the broad context of astrobiology through a combined laboratory, numerical, analytical, and field investigations. Icy Worlds team pursues this goal through four major investigations namely, the habitability, survivability, and detectability of life of icy worlds coupled with “Path to Flight” Technology demonstrations. A search for life linked to the search for water should naturally “follow the ice”. Can life emerge and thrive in a cold, lightless world beneath hundreds of kilometers of ice? And if so, do the icy shells hold clues to life in the subsurface? These questions are the primary motivation of our science investigations

    ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.1 3.2 4.1 5.1 5.2 5.3 6.2 7.1
  • Biogenic Gases From Anoxygenic Photosynthesis in Microbial Mats

    This lab and field project aims to measure biogenic gas fluxes in engineered and natural microbial mats composed of anoxygenic phototrophs and anaerobic chemotrophs, such as may have existed on the early Earth prior to the advent of oxygenic photosynthesis. The goal is to characterize the biogeochemical cycling of S, H, and C in an effort to constrain the sources and sinks of gaseous biosignatures that may be relevant to the detection of life in anoxic biospheres on habitable exoplanets.

    ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1 6.2 7.2
  • Biosignatures in Ancient Rocks – Kump Group

    We are analyzing FAR-DEEP cores that span the putative “oxygen overshoot” associated with the termination of the Great Oxidation Event, 2.0 billion years ago. The volcanic rocks in question are highly oxidized. Our hypothesis is that oxygen-enriched groundwaters altered these rocks during a time interval when atmospheric oxygen concentrations approached modern levels, falling subsequently to lower values characteristic of the ensuing billion years. Kump has also proposed a new explanation for the “second rise of atmospheric oxygen” in the Neoproterozoic (ca. 850 Ma).

    ROADMAP OBJECTIVES: 1.1 4.1 4.2 4.3 5.2 6.1
  • Project 3: The Origin of Homochirality

    A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. We are calculating the way in which this can take place using statistical mechanics, and also trying to see how a uniform homochirality could be stable to spatial fluctuations.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 5.2 7.1 7.2
  • Early Animals: Modeling the Biotic-Abiotic Interface in the Early Evolution of Multicellular Form

    The size of early multicellular organisms was sufficint to modify their local environment. Our initial work modeling of Neoproterozoic frond-like forms in the earliest-known communities of multicellular organisms demonstrates they were of sufficient scale and density to generate a distinctive canopy flow-regime. This modified environment yielded a selective advantage towards large eukaryotic forms that evolved at this time. This result is a function of limits imposed by diffusion at the surface of organisms, and how height and attendant velocity exposure escape these limits. Building on these results, we are now developing additional models of abiotic/biotic interactions at organismal surfaces, which are implicit in the morphology, development and orientation of other Neoproterozoic fossils. Ultimately, this work will help illuminate how forms initialy dependent on passive diffusion became more trophically complex, yielding a transition to the animal radiation.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Coupled Energy Balance Ecosystem-Atmosphere Modeling of Thermodynamically-Constrained Biogenic Gas Fluxes Project

    The thermodynamically-constrained fluxes of gases to and from a biosphere has profound, planet-wide consequences. These fluxes can directly control the redox state of the surface environment, the atmospheric composition, and the concentration of nutrients and metals in the oceans. Through these direct effects, they also create strong forcings on the climate, the redox state of the interior of the planet, and the detectability of the biosphere by remote observations. This is a theoretical modeling study to constrain biomass, productivity, and biogenic gas fluxes given a range of geologic parameters.

    ROADMAP OBJECTIVES: 1.1 1.2 5.2 5.3 6.1 7.2
  • Project 4: Rapid Evolution in Stressed Populations: Theory

    Evolution is typically thought of as occurring over millions of years. But recently it has become clear that we have grossly over-estimated this time scale. Perhaps the most famous example of this is the rapid evolution of resistance of bacteria, worldwide, to modern antibiotics. Similarly, early life has an evolution time scale problem: given the age of the Earth and the known age of the Last Universal Common Ancestor, life must have arisen and evolved the majority of the complexity of the modern cell in less than a billion years. This project is a theoretical attempt to understand how a fluctuating environment can accelerate evolution rate, and lead to evolution on ecosystem time scales. Eventually, this work will join up with the experimental work being done by our team, using the GeoBioCell, in Project 8.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 5.2 5.3 6.1
  • Project 5: The Origins of Life’s Diversity

    The huge diversity of life poses a major challenge to ecological theory and a major source of optimism for astrobiology. Ecological theory argues that a single environmental niche should be colonized by a single species of organism, or perhaps a small community, and so the diversity of life should be essentially a measure of the number of niches present. The huge diversity of life does suggest, however, that the ability of life to explore, colonize and especially create environmental niches has been drastically underestimated. Accordingly, the likelihood of extraterrestrial life arising is also underestimated, or at least inadequately estimated, by our present understanding of biological evolution. This project attempts to solve this problem by developing a new theory for niche diversity.

    ROADMAP OBJECTIVES: 3.4 4.1 4.2 5.1 5.2 5.3 6.1 6.2
  • Biosignatures of Life in Ancient Stratified Ocean Analogs

    Instigated by Macalady and Kump in 2010, this project investigates biosignatures of life in modern analogs for stratified ancient and/or extraterrestrial oceans. The primary field site is a sinkhole in Florida. Other field site include stratified ocean analogs in the Bahamas, New York State, and the Dominican Republic. A website monitoring the activities of an informal working group on Early Earth Photosynthesis is maintained by Macalady (http://www.geosc.psu.edu/~jlm80/EEP.html).

    ROADMAP OBJECTIVES: 2.1 3.3 3.4 4.1 5.2 5.3 6.1 7.1 7.2
  • Project 6. Mining Archaeal Genomes for Signatures of Early Life: Comparison of Metabolic Genes in Methanogens

    Methanogenic archaea derive energy from simple starting materials, producing methane and carbon dioxide in the process. The chemical simplicity of the growth substrates and versatility of the organisms in extreme environments provide for a possibility that they could exist on other planets. By characterizing the evolution of methanogens from the most simple to most complex organism as well as their growth characteristics under controlled environments, we hope to address the question as to whether they could exist on planets such as Mars, where bursts of methane have been seen, yet no source has yet been identified.

    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 7.2
  • Jon Toner NAI NPP Postdoc Report

    Aqueous salt solutions are critical for understanding the potential for liquid water to form on icy worlds and the presence of liquid water in the past. Salty solutions can form potentially habitable environments by depressing the freezing point of water down to temperatures typical of Mars’ surface or the interiors of Europa or Enceladus. We are investigating such low-temperature aqueous environments by experimentally measuring the low temperature properties of salt solutions and developing thermodynamic models to predict salt precipitation sequences during either freezing or evaporation. These models, and the experimental data we are generating, are being applied to understand the conditions under which water can form, the properties of that water, and what crystalline salts indicate about environmental conditions such as pH, temperature, pressure, and salinity.

    ROADMAP OBJECTIVES: 2.1 5.2 5.3
  • Planetary Surface and Interior Models and SuperEarths

    We use computer models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to determine the initial characteristics that are most likely to contribute to making a planet habitable in the long run. Observations in our own Solar System show us that water and other essential materials are continuously consumed via weathering (and other processes: e.g., subduction, sediment burial) and must be replenished from the planet’s interior via volcanic activity to maintain a biosphere. The surface models we are developing will be used to predict how gases and other materials will be trapped through weathering and biological processes over time. Our interior models are designed to predict tidal effects, heat flow, and how much and what sort of materials will come to a planet’s surface through resurfacing and volcanic activity throughout its history.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • Project 9: Evolution Through the Lens of Codon Usage

    The sequences of protein encoding genes are subject to multiple levels of selection. First, amino acid changes that adversely alter protein function are unlikely to survive. In addition, the genetic code of organisms is degenerate; it includes alternative (synonymous) codons for most of the amino acids. Codon usages in a genome are generally viewed as a balance between drift and selection for rapid and accurate translation of mRNAs into proteins. This balance defines the native codon usage of the organism. Later, it was recognized that many horizontally transferred genes have distinctive codon usages. It was assumed that these reflected the codon usages of the organisms that contributed the genes. We viewed this as an opportunity to identify those sources.

    These studies of this have led us to discover that: (i) most of the recently acquired genes come from such closely related organisms that their distinctive codon usages cannot be attributed to a phylogenetically distant source; (ii) the transfers commonly exceed recognized boundaries of microbial species; (iii) after their acquisition, some of the genes do not drift to match the native codon usage of the recipient; (iv) many of the genes that are most up-regulated under starvation conditions have this same codon usage; and (v) a distinctive stress/starvation-associated codon usage is a recurring theme that is observed in diverse Bacteria and Archaea.

    These studies entailed the development of a variety of new codon usage analysis tools. We are making these tools available, and are integrating them into the RAST genome annotation and analysis server at Argonne National Laboratory.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3
  • Stoichiometry of Life – Task 1 – Laboratory Studies in Biological Stoichiometry

    This project component involves a set of studies of microorganisms with which we are trying to better understand how living things use chemical elements (nitrogen, phosphorus, iron, etc.) and how they cope, in a physiological sense, with shortages of such elements. For example, how does the “elemental recipe of life” change when an organism is starved for phosphorus or nitrogen or iron? Is this change similar for different species of microorganisms? Are the changes the same if the organism is limited by a different key nutrient? Furthermore, how does an organism shift its patterns of gene expression when it is starved by various nutrients? This will help in interpreting studies of gene expression in natural environments.

    ROADMAP OBJECTIVES: 5.2 5.3 6.1 6.2
  • Molecular Biosignatures of Redox-Sensitive Bacteria and Hyperthermophiles

    The Summons lab has been researching a range of molecular and isotopic phenomena aimed at shedding light on what controls Neoproterozoic ocean redox, evolutionary trends in the abundances of molecular fossils (biomarkers) and the enigmatic natural variability carbon isotopic compositions of organic and inorganic carbon at this time. Our studies of carotenoid pigment biomarkers for green and purple sulfur bacteria have revealed that they are ubiquitous in rock extracts of Proterozoic to Paleozoic age—implying that the shallow oceans became sulfidic more frequently than previously thought. Other projects focused on the biosynthesis of another important biomaker, the hopanoids, vesicles released from marine bacteria for interaction between cells and their environment, and the molecular signatures of microbial communities in hot springs in Yellowstone National Park.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 5.2 7.1
  • Project 2E: Carbonate-Associated Sulfate (CAS) as a Tracer of Ancient Microbial Ecosystems

    The chemical compound sulfate is present in ocean water and ratios of its stable isotopes of sulfur and oxygen have varied over geological time and are indicators of global geochemical processes. Other researchers have extracted trace amounts of sulfate from carbonate minerals of various ages as a glimpse into the Earth’s geological past. We are, however, applying this approach to carbonate minerals formed by microbial processes during burial of sedimentary rocks, which we hoped would give information on the microbial ecosystems. We needed to modify and develop existing methods for extracting the trace amounts of sulfate because our samples would be mineralogically much more complex. Initially, just to test the method we tried it on material from the local Monterey Formation rocks, which are of Miocene age (approx. 13 My old) and were delighted to find that the results enabled us to see the workings of a very complex microbial ecosystem with at least three different sorts of metabolism operating.

    ROADMAP OBJECTIVES: 5.2 6.1 7.1
  • Stoichiometry of Life, Task 2a: Field Studies – Yellowstone National Park

    Yellowstone National Park harbors an array of hydrothermal ecosystems with widely varying geochemical characteristics and microbial communities. Our research aimed to understand how the geochemistry of these hot springs shapes their constituent microbial communities including their composition and function. To accomplish this aim, we measured (1) physical and geochemical properties of hot spring fluids and sediments, (2) the rates of biogeochemical processes (i.e., methane oxidation, nitrogen fixation, microbial Fe cycling, photosynthesis, de-nitrification, etc.), and (3) markers for microbial community diversity (i.e., SSU rRNA, metabolic genes, lipids, proteins).

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.2
  • Stoichiometry of Life – Task 2b – Field Studies in Cuatro Cienegas

    We performed two studies to evaluate ecological impacts of nitrogen and/or phosphorus fertilization in a P-deficient and hyperdiverse shallow pond in the valley of Cuatro Cienegas, Mexico.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2
  • Understanding Past Earth Environments

    This year, this interdisciplinary effort continued on two major fronts. First, we furthered the development and use of new techniques that help us characterize environmental conditions on ancient Earth. This included progress on our development of a technique for estimating the atmospheric pressure on Archean Earth, and the development and use other techniques for analyzing the chemistry of Archean lakes. We also used our existing models of ancient Earth to simulate other conditions consistent with the conclusions reached from these laboratory analyses.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
  • Stoichiometry of Life – Task 2c – Field Studies – Other

    We performed biogeochemical and microbiological studies of novel aquatic habitats, floating pumice in lakes of northern Patagonia that were derived from the 2011 eruption of the Puyehue / Cordon Caulle volcano in Chile.

    ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1
  • Task 3b: Ancient Records – Genomic

    Task 3b team members are involved in deciphering genomic records of modern organisms as a way to understand how life on Earth evolved. At its core, this couples the integrated measurement and modeling of evolutionary mechanisms that drove the differences between extant genomes (and metagenomes), with experimental data on how environmental dynamics might have shaped these differences across geological timescales. This goal draws from team members’ expertise encompassing theoretical and computational biology, microbial evolution, and studying life in both extreme and dynamic environments across the planet.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3
  • Task 4: Biogeochemical Impacts on Planetary Atmospheres

    Oxygenation of Earth’s early atmosphere must have involved an efficient mode of carbon burial. In the modern ocean, carbon export of primary production is dominated by fecal pellets and aggregates produced by the animal grazer community. But during most of Earth’s history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. In this task we experiment with the marine cyanobacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. We have found that these minute cyanobacteria form aggregates in conditions that mimic the open ocean and can sink gravitationally in the water column. Experiments with added clay minerals (bentonite and kaolinite) that might have been present in the Proterozoic ocean, show that these can accelerate aggregate sinking. In addition we find that Synechococcus could potentially export carbon 2–3 times of that contained in their cells via aggregation, likely due to the scavenging of transparent exopolymer particles and dissolved organic matter. Thus, aggregation and sinking by these small cyanobacteria could have constituted an important mode of carbon export in the Proterozoic ocean.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2
  • Project 3D: A Microbial Iron Shuttle in Early Earth Marine Basins

    Iron-based metabolisms are deeply rooted in the tree of life, and yet comparatively little attention has been paid to searching for Fe-based biosignatures as compared, for example, photosynthetically-based metabolisms. Dissimilatory Iron Reduction (DIR) is found in both Archaea and Bacteria domains of life, its electron acceptors and donors are widespread in the solar system. This project focuses on determining the basin-scale footprint of DIR in well preserved samples of Mesoarchean age (~3 Ga) in the Witwatersrand Supergroup of South Africa. Preliminary results show a trend of iron enrichment that correlates with δ56Fe depletion from the proximal shelf to the deep distal basin, which is interpreted to indicate a DIR-driven “iron pump” or “shuttle”, where microbially-produced aqueous Fe(II) on continental shelves was pumped to the deep basin and trapped as Fe-bearing sulfides or oxides. These results not only confirm that Fe-based metabolisms were important on the early Earth ~3 b.y. ago, but that it had a substantial “footprint” in the biosphere on a basin-wide scale.

    ROADMAP OBJECTIVES: 4.1 5.2 6.1 7.1 7.2