2015 Annual Science Report
Astrobiology Roadmap Objective 5.1 Reports Reporting | JAN 2015 – DEC 2015
Roadmap Objective 5.1—Environment-dependent, molecular evolution in microorganisms
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
Project 1: From Generalist to Specialists (Or Not): A Case Study in Enzyme Evolution
Metabolic enzymes, although prodigious catalysts, are not perfectly specific for their physiological substrates. They typically possess secondary activities as a consequence of the assemblage of highly reactive functional groups, metal ions and cofactors in their active sites. Secondary activities that are physiologically irrelevant, either because they are too inefficient to contribute to fitness or because the enzyme never encounters the substrate, are termed promiscuous activities.
Promiscuous activities are important from an evolutionary standpoint because they provide a reservoir of catalytic potential within a proteome that can be drawn upon when the environment changes. A promiscuous activity may become important for fitness when a new source of carbon, nitrogen or phosphorous appears in the environment, or when a previously available compound, such as an amino acid or cofactor, becomes unavailable. A promiscuous activity may also become critical when the organism is exposed to a novel toxin, such as an antibiotic or pesticide.
A newly recruited promiscuous activity is unlikely to be the optimal solution to an environmental challenge or opportunity. In this project, we are using a model system in E. coli to characterize the genetic changes by which a gene encoding an enzyme whose promiscuous activity has become essential for growth duplicates and diverges to encode a pair of genes encoding efficient specialist enzymes. This work will provide a better understanding of the process by which large superfamilies of enzymes have diverged from generalist enzymes in the last universal common ancestor.ROADMAP OBJECTIVES: 5.1 5.3 6.2
Understanding Past Environments on Earth and Mars
In this task we performed research to understand the evolution of habitable environments on Earth and Mars, both of which serve as potential analogs for habitable environments on extrasolar planets. We are expanding this line of work from past reports to span the entire histories of both planets. On Earth, we have sought to understand environments and time periods spanning the origins of life to the effects of human-generated greenhouse gas emissions on modern-day climate cycles. On Mars, we focus on the ancient conditions that could have allowed liquid water to be stable at the surface; on modern Mars, we focus on the debate on the presence, amount, and variability of methane in the Martian atmosphere.ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
Field Activities at the Coast Range Ophiolite Microbial Observatory (CROMO)
CROMO provides ongoing excellent exposure to samples of ophiolite-hosted serpentinites and associated rocks, access to monitoring wells important for observing serpentinization-related groundwater flow regimes, and serves as a community-building platform that fosters new scientific collaboration. CROMO has served as a test-bed for refining new experimental approaches, and progressing from basic observations to more complex, multi-disciplinary science.
Within the past year, studies at CROMO have focused on the subsurface hydrogeochemical dynamics, by monitoring groundwater hydrology, measuring the concentrations and composition dissolved iron, sulfur, dissolved inorganic carbon, major inorganic anions and cations, dissolved hydrogen, carbon monoxide and methane gases, and organic compounds, in addition to time-series analyses.
CROMO datasets are being incorporated into an exploratory database project aimed at addressing NASA’s public data requirements. Once developed, this database will help to address data sharing plans for collaborators and serve as a valuable tool for CROMO data management across collaborating labs.
In 2015, project members Dawn Cardace, Masako Tominaga, Michael Kubo, Lauren Seyler, Mary Sabuda, Abigail Johnson, Ken Wilkinson, & Cameron Hearne participated in a field trip to CROMO from August 21-27, to continue seasonal bio/geo/chemical monitoring of the wells, as well as assessing the site for future geophysical measurements.ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.1 7.2
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
Project 1C: Analysis of Dissimilatory Iron-Reducing Microbial Communities in Chocolate Pots Hot Spring, Yellowstone National Park
This study represents the first targeted exploration of the active microbial community at source vent of Chocolate Pots hot springs (CP), a warm, circumneutral pH hot spring in Yellowstone National Park. This work was motivated by previous in vitro dissimilatory iron reducing (DIR) incubations of the native microbial community present in the Fe(III) oxide deposits (hereafter referred to as “CP oxides”) near the vent. DIR has the potential to generate distinct signatures of microbial Fe redox metabolism, and identification of the microbial assemblages involved in this metabolism is important for making a concrete linkage between biological metabolism and the generation of geochemical and isotopic biosignatures in relation to redox gradients on Earth and other rocky planets. The central goal of this study was to obtain a phylogenetic and metagenomic characterization of the active acetate-oxidizing DIR community at CP using 13C stable isotope probing (SIP) techniques. CP oxide sediments and spring water were collected from the CP vent source and used to initiate in vitro SIP incubations using labeled (13C) and unlabeled acetate. Incubations targeted the active microbial community which is capable of coupling the oxidation of acetate to DIR. The SIP results allowed us to clearly separate the active acetate-metabolizing microbial community from the rest of the community and identify which organisms native to CP make up this population. The role of some members of this community can be inferred with reasonable confidence from the phylogeny of the OTUs from the amplicon libraries (e.g. Geobacter, Ignavibacteria), and the design of the incubations. The metabolic role of other dominant taxa is less well understood at this point and we are preparing to submit samples for shotgun metagenomic sequencing to address these questions.ROADMAP OBJECTIVES: 2.1 4.1 5.1 5.3
Project 3: Consequences of recA Duplication for Recombination, Genome Stability and Fitness
Homologous recombination (HR) – the exchange of genetic information between similar DNA molecules – is an ancient process that is central to the emergence of biological complexity, diversity and stability. Yet, it must be tightly regulated, as it is likewise an important source of destabilizing genomic rearrangements. Despite the importance of HR, we still have a poor understanding of the balance of these creative, stabilizing and destabilizing contributions to organismal fitness, complexity and genome evolution. We are using the extraordinary genome evolutionary dynamics and duplicated copies of the HR gene recA in the cyanobacterium Acaryochloris as a model to gain novel insights on the fitness consequences that emerge from the interplay between HR-mediated maintenance of genome stability, selectively favored gene duplications and non-adaptive genomic rearrangements.ROADMAP OBJECTIVES: 4.2 5.1 5.3 6.1 6.2
Project 4: Co-Evolution of Escherichia Coli and Its Parasite Bdellovibrio Bacteriovorus: An Experimental Model for Eukaryogenesis
This project seeks to address a long-standing question in the early evolution of life on Earth: how and why did simpler cell types (prokaryotes) transition into more complex (eukaryotic) cells (i.e. eukaryogeneis)? Because this conversion happened millions of years ago and left scant fossil evidence, we have been attempting to “re-create” a similar transformation in the lab that can be easily manipulated and studied in detail. A greater understanding of the events that ocurred both before and after eukaryogenesis will not only help NASA scientists predict what extraterrestrial life might look like, it will also help us understand how modern eukaryotic cells function and evolve.ROADMAP OBJECTIVES: 3.3 3.4 5.1 6.2
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
Project 5: Adaptation, Mutation Supply, and Evolution of Synergy in Biofilm Communities
We will quantify the dynamics of adaptation and identify the mutational causes in evolving biofilms with high precision, and therefore illustrate how microbes colonizing a new surface can transform their environment and set the stage for primitive multicellularity. Biofilms resemble tissues in their subdivided labor, varied physical structure and shared metabolism. We predict that the stability of this ecological cooperation rests on population-genetic controls on selfish lineages associated with mutators, much as tissues are liable to selfish invasion by cancers.ROADMAP OBJECTIVES: 4.2 5.1 5.2 6.1 6.2
RPL and Expedition 357: Serpentinization and Life at the Atlantis Massif
Circulating hydrothermal fluids associated with mid-ocean ridges represent some of the most prominent examples of the intersection between chemical energy and the biosphere. The Lost City Hydrothermal Field, which sits atop the Atlantis Massif near the Mid Atlantic Ridge hosts a microbial ecosystem which feeds off the products of serpentinization. IODP Expedition 357, which sailed in Fall 2015, obtained rock cores and fluids from the Atlantis Massif, which are being used for the coordinated investigation of serpentinization processes and life. Lost City is known to sustain abiogenic organosynthesis reactions and as such has been suggested to be an analogue to prebiotic early Earth environments and potential extraterrestrial habitats.ROADMAP OBJECTIVES: 3.1 3.4 5.1 5.2 5.3 7.2
Mars Analogs: Habitability and Biosignatures in the Atacama Deser
This project focuses on the study of habitability in the Atacama Desert of northern Chile, one of the driest regions on Earth. We want to understand how life adapts and survives in an environment where liquid water is exceedingly rare, and how biosignatures are preserved in that environment after microorganisms die. These studies can become a very useful guide for future robotic missions to Mars. This year we focused on microbial communities that inhabit the interior of salt nodules in evaporitic lake deposits. These are the only known active microbial comunities in the driest parts of the Atacama. We wanted to understand how these microbial communities survive in an environment that excludes every other form of life. We suspected that the salt communities use atmospheric water vapor as a source of water to run their metabolic processes. We showed that this is indeed the case with a combination of field and laboratory tools. Our results suggest that the salt substrate could be one of the last possible habitats for life in extremely dry environments.ROADMAP OBJECTIVES: 2.1 5.1 5.3 6.1 6.2 7.1 7.2
Project 5: Control of Evolvability and Chromosomal Rearrangement by Stress
Using a bacterial system, we are investigating the regulation of genomic change by stress, both small changes in DNA sequence and larger chromosomal rearrangements. That mutation rates should be regulated by stress has wide significance for understanding mechanisms of evolution. Our major goal in this project is to discover how the general stress-response regulator switches from accurate modes of DNA repair to error-prone modes. We have established that mutation under stress only occurs if there are replicating blocking lesions in DNA, usually formed by reactive oxygen. We have shown apparent positive and negative regulation of the levels of oxygen radicals. We are now working to discover the origin of the radicals so that we can ask whether radicals form as an unavoidable byproduct of respiration, or whether this represents a dedicated mechanism to instigate mutation, and hence evolution.ROADMAP OBJECTIVES: 5.1
Project 6: The Evolution of Complexity via Multicellularity and Cellular Differentiation
The evolution of multicellular organisms from single-celled ancestors set the stage for unprecedented increases in complexity, especially in land plants and animals. We have used the unicellular green alga Chlamydomonas reinhardtii to generate de novo origins of simple (undifferentiated) multicellularity in two separate experiments. Using these experimentally evolved algae, we will ascertain the genetic bases underlying the evolution of multicellularity, evaluate the role of genetic assimilation in the evolution of multicellularity, and observe the evolutionary origin of multicellular development in real time.ROADMAP OBJECTIVES: 4.2 5.1 6.2
Subglacial Environments as Water‐Rock Hosted Microbial Ecosystems
Glaciers, ice sheets and ice caps cover ~11% of the earth’s surface, and likely covered up to 100% during Neoproterozoic glaciations. The beds of these ice masses can have significant sectors at the pressure melting point. The resulting water lubricates ice sliding and accelerates erosion, provides habitat for subglacial microbial ecosystems, and may have acted as refugia during past global glaciations on Earth. Such environments may also act as habitats for life on other planetary bodies.
Grinding of bedrock by glaciers exposes fresh mineral surfaces capable of sustaining microbial metabolism. The foci of RPL investigations on subglacial environments are categorized into two key areas of relevance to habitability studies: i) determine the extent to which minerals support chemotrophic metabolism and the production of biosignatures (e.g., weathering products), and ii) quantifying the influence of water-rock interactions in supplying substrates to support energy metabolism. Through these interdisciplinary and collaborative studies, we aim to characterize the active microbial processes in subglacial environments and to define the sources of energy that sustains this microbial life.ROADMAP OBJECTIVES: 2.1 5.1 5.2 5.3 6.1 6.2 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
Biosphere-Geosphere Stability and the Evolution of Complex Life
Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with a significant perturbation of Earth’s carbon cycle. But there are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? We hypothesize that mass extinctions are associated with an instability in the carbon cycle. This project attempts to specify, both theoretically and empirically,the conditions that result in such an instability.ROADMAP OBJECTIVES: 4.3 5.1 5.2 6.1
Project 8: Limits to Optimality in Adaptive Evolution
The goal of this project is to determine how the genetic makeup of an organism influences its future evolution. We have developed a tracking system that allows us to track the emergence of mutations that make an organism more fit in a certain environment – we will be deploying this system to track such emergences in yeast strains with slightly different genetic makeup. This will allow us to see how the genetic makeup influences the evolutionary process.ROADMAP OBJECTIVES: 5.1 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
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
Mars Analog Studies: Ice Covered Lakes on Earth and Mars
Ice-covered lakes in Antarctica provide models for sedimentary processes on ancient Mars and microbial ecosystems for early Earth. Ice affects sedimentation because sand grains can be blown onto the ice, where they can eventually go through the ice into the lake below. Understanding the details of these processes and resulting sediments will allow us to better reconstruct details of lake environments and their implications for climate on early Mars. Early Earth ecosystems, and those on early Mars if life ever existed there, consist exclusively of microorganisms, which is also true for many Antarctic lakes. Thus, these lakes provide the opportunities to investigate ecological principles for early ecosystems. Data from the microbial mats in these lakes are providing insights into the growth of stromatolite, the geochemical impacts of oxygen-producing photosynthesis, and environments that may have promoted the early diversification of animals.ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1
Project 10: 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 is degenerate; it includes alternative (synonymous) codons for most of the amino acids. The codon usages of genes reflect a balance between drift and selection for rapid and accurate translation of mRNAs into proteins, and in the case of horizontally transferred genes, the codon usages of their sources. Our studies of genes and their codon usages 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) some genes do not drift to match the native codon usage of their current genome, but resemble the most recently acquired genes; (iv) many of the genes that are most up-regulated under starvation conditions also have this codon usage; and (v) a distinctive stress/starvation-associated codon usage is a recurring theme that is observed in diverse Bacteria and Archaea.
These results have changed our understanding of the dynamics with which genetic novelties are shared in the biosphere, and revealed that there are selective forces on codon usage beyond those currently appreciated in the field.ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1
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
Taphonomy of Microbial Ecosystems
We perform experiments to understand shapes, molecules and isotopic signals of microbial processes in modern and old sediments. Experimental studies of microbial interactions with sediments, ions in the solution and the flow help us elucidate mechanisms that may have shaped sandy surfaces and preserved fossils on these surfaces at the dawn of animal life. Culture-based studies of isotopic fractionations produced by microbial processes and microbial membrane lipids help us interpret corresponding signals in the rock record and modern environments.ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1 7.1 7.2