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Executive Summary

Iron-sulfur clusters are ubiquitous in biology and possess features that are reminiscent of the features of iron-sulfur minerals. The structure/reactivity relationships between iron-sulfur metalloenzymes and iron-sulfur minerals has been noted by a number of investigators and is the basis for aspects of a “Metabolism First” origin of life scenario and more specifically for the “Iron Sulfur World”. These provide a framework for the research being conducted at the Astrobiology Biogeocatalysis Research Center with a focus on revealing the connection between iron-sulfur minerals and iron-sulfur metalloenzymes. The adaptation of iron-sulfur motifs from the abiotic world to the biological world may have been an early event in the generation of the building blocks of life on Earth and possibly a common feature of life elsewhere in the universe. ABRC research is aimed at providing the structural and chemical determinants that define the catalytic properties of iron-sulfur-based minerals and biological catalysts using the examples of hydrogen activation and evolution, and nitrogen reduction as model reactions. An overarching goal of the ABRC is to provide new insights into processes by which iron-sulfur motifs may have transitioned from the abiotic to biotic world. The results of the center’s efforts will support the mission of NASA in the area of prebiotic chemistry and has the potential to contribute significantly in the development of mineral signatures for terrestrial and extraterrestrial life.
The ABRC is a unique and important component of the NASA Astrobiology Institute. The ABRC focuses on the abiotic chemical interconversions that result in the formation of the raw materials or reactants necessary for various condensation reactions that can result in the formation of the basic building blocks of life. The ABRC’s efforts are focused mainly on laying the fundamental groundwork for Goal 3 of the NASA Astrobiology Roadmap (Understand how life emerges from cosmic and planetary precursors) of the NASA Astrobiology Roadmap. Furthermore, ABRC research directly impacts the objectives of Goals 2 (Determine any past or present habitable environments, prebiotic chemistry and signs of life elsewhere in our Solar System), and 4 (Understand how life on Earth and its planetary environment have co-evolved through geological time). The outcomes of the research will also provide the basis for aspects of Goal 7 (Determine how to recognize signatures of life on other worlds and on early Earth). Our recently developed experimental thrust in developing new approaches for examining iron-sulfur enzyme evolution will contribute significantly to Goal 5 (Understand the evolutionary mechanisms and environmental limits of life) as well. The ABRC’s research focus provides a logical and synergistic complement to research efforts of other Astrobiology Research Centers.
Specifically, ABRC research is focused on investigating (bio)synthesis, structure, and reactivity at iron-sulfur motifs and is divided into three major thrust areas including 1) iron-sulfur mineral catalysis, 2) iron-sulfur enzyme catalysis, and a 3) synthetic or mimetic thrust that is aimed at bridging our understanding of the relationships between structure and reactivity at the active sites of Fe-S enzymes and the structure and reactivity of Fe-S minerals.

During the current year of support we have developed a complementary project examining iron-sulfur enzyme evolution by examining the evolutionary trajectory of genes involved in iron-sulfur cluster biosynthesis. Coupling the examination of the evolutionary trajectory of multiple gene loci in the context of gene duplication and fusion events provides a robust means to assign evolutionary paths and evolutionary origins of processes catalyzed by iron-sulfur enzymes. In some cases, there are clear prospects for tying these evolutionary relationships to the geologic record with a promise for gaining significant insights into the nature of life on early Earth. In sum, these activities are aimed at examining the potential role of iron-sulfur motifs at the transition between the non-living and the living Earth. Moreover, we complement our scientific investigations with activities that evaluate both metaphysical and philosophical implications of the origin of life. In addition, a strong education and public outreach component with activities associated with nearby Yellowstone National Park with its numerous thermal features having characteristics often associated with analogs of early Earth as a means to engage public audience of all ages. These activities are aimed at educating public audiences on the mission of NASA Astrobiology and illustrate important fundamental principles of chemistry and biology.

Specific research activities in the three research areas are described below:

1. Detailed studies on iron-sulfur enzymes are being conducted in order to evaluate the connection among iron-sulfur-based catalysis in minerals, clusters, and biocatalysts. The emphasis of this work has been the biological mechanisms for iron-sulfur cluster synthesis and the role in radical chemistry in this process together with the characterization of the structural, physical and catalytic properties of complex iron-sulfur cluster containing hydrogenases and nitrogenases.
2. Catalysis at iron-sulfur mineral surfaces is being investigated in aqueous and gas phase systems as models of prebiotic chemical transformations. The emphasis of this thrust is to probe the properties of synthetic mineralized surfaces, the impact of surface defects and modifications on the physical and catalytic properties of an iron-sulfur mineral surface, the effect of energy (photo, redox, thermal, mechanical), pH, concentration, partial pressure of gases, surface area, and length scale on the structural, physical, and catalytic properties of iron-sulfur clusters, particles and minerals, and materials studied by beam/surface collision experiments, advanced spectroscopic techniques, and structural modeling of mineral surface defects by integrated quantum chemical methods.
3. Synthetic approaches are being utilized to bridge the gap between iron-sulfur minerals and highly evolved biological iron-sulfur metalloenzymes. For this thrust we use as a basis the ligand arrangements we see in the highly catalytically active enzymes. Using synthetic platforms that allow us to introduce a variety of ligands found in the native enyzmes and examine the structural determinants of catalysis. This experimental line puts us in a better position to rationalize a stepwise trajectory from modified iron-sulfur minerals via organic nested clusters to the highly evolved iron-sulfur enzymes that are an important elements of biology today.
Through the first three years of support, the ABRC has grown in scope primarily through the development of research thrusts in the area of molecular evolution and microbial ecology that truly embrace and provide a strong complement to the major theme of the project examining iron-sulfur enzymes and catalysis of key prebiotic reactions at iron-sulfur minerals and their derivatives. We are probing iron sulfur enzyme evolution by keying on specific genetic events such as gene fusions and gene duplications and interrogating multiple gene clusters in concert for robust phylogenetic analyses. Evolutionary links between the enzymes of main interest and components of photosynthesis provides the basis for calibrated molecular clock experiments that will allow us to link the evolutionary record to the geological record. In our microbial ecology work we are mapping the occurrence of iron-sulfur enzymes as a function of environment. This function-based perspective on habitability provides insights into the nature of environments where certain iron-sulfur enzymes occur and predominate and provide insights into environmental underpinnings that may have been key to their evolutionary origins. In addition, with support from the NAI Director’s discretionary fund we have been able expand our model complex iron-sulfur enzymes to include carbon monoxide dehydrogenase / acetyl CoA synthase complexes. A natural complement to our ongoing activities that involves a valuable collaboration with Michael Russell of the JPL Icy Worlds Team and Greg Ferry of Penn. State’s PSARC. Other value additions to our teams Astrobiology research portfolio include; 2) examining archaeal virus evolution and the potential importance of viruses in the origin and evolution of life on Earth; probing subglacial microbiology emphasizing methanogenesis as well as carbon and nitrogen cycling; biomineralization and molecular level signatures of life; and theoretical studies probing chemical reactions and chemical networks in interstellar media.

ABRC Research Highlights

In this third year of support we have really turned the corner and have very recent seminal results in all of the major thrust areas of the project. These results provide strong proof of concept for the original emphasis of our center and experimental design of the individual elements of the project. Perhaps more importantly however, is that these results provide the basis to more clearly see the next generation of our center’s research. In addition to the results described below on the main thrusts of ABRCs other key results include results implicating biological methane production in subglacial sediments, high temperature nitrogen fixation in thermal acidic terrestrial environments, and new approaches to identify viruses in environmental samples.

Our studies on iron-sulfur enzymes have really emphasized understanding the biosynthetic pathways by which the unique non protein ligands are generated and linked to cluster metal ions. Our rationale for emphasizing biosynthesis is that the novel modifications that are made to the active site cofactors of hydrogenases and nitrogenases are the key to their unique catalytic properties. We are particular interested in whether the chemical reactivity that results in iron-sulfur cluster modification in biology are of the nature of chemical reactions we can envision to occur prebitoically. Our research in this past year has revealed that the key reactions involved in introducing nonprotein ligands in both nitrogenases and certain hydrogenases are iron-sulfur enzymes that function through radical based reactions. Radical based reactions at iron-sulfur motifs are indeed reactions we can envision could occur under prebiotic conditions and provide the basis for further experimentation attempting modifications to iron-sulfur minerals in the same manner to probe whether modification promote nitrogen reduction or reversible hydrogen oxidation reactivity. These results together with the results of our new molecular evolution arm of the project indicate that the cluster biosynthesis pathways evolved on a different trajectory than the structural genes for the enzymes. This suggests that biosynthetic enzymes are recruited stepwise and that cluster evolution occurs stepwise in much the same manner as one might envision that modifications are made to minerals to refine higher orders of prebiotic reactivity. Since the radical based chemistry and the role of radical SAM enzymes has been found to be so critical in complex iron-sulfur cluster biosynthesis, we have staked out a new thrust area to address radical SAM functional diversity and evolution specifically and we have been able to already identify additional roles for radical SAM enzymes in metal cofactor biosynthesis. Our combined biochemical and phylogenetic approach has provided the basis to conclude that specifically [FeFe]-hydrogenases and Mo-nitrogenases are not likely to be primordial and their evolution. The studies have identified key unifying principles in nitrogenase iron-molybdenum cofactor and hydrogenase H cluster biosynthesis and new ways to think about their evolution that we can now address experimentally. For example, using what we know of nitrogenase iron-molydenum cofactor biosynthesis biochemical we have been able to conduct a muliple gene loci phylogenetic analysis that keys on a specific gene fusion event and a pair of gene duplication events, we have been able to show that amongst extant organisms the oldest nitrogenases occur in the genomes of hydrgenotrophic methanogens and amongst bacteria the oldest nitrogenases appear to be associated with certain firmicutes.

In our mineral thrust we have had an equal measure of breakthrough success. Progress has been made in defining competitive abiotic pathways for reducing nitrogen compounds to ammonia from nitrogen oxides relative to the dinitrogen. Using pyrite mineral surfaces and freshly precipitated Fe-S particles, we showed that under hydrothermal conditions nitrite (NO^2-), nitrate (NO^3-), as well as nitric oxide (NO) can be converted to ammonia to comparable yields than starting from dinitrogen (N₂). Formation of ammonia or ammonium ion in aqueous solution is considered as an essential step toward creating amino acids that are key building blocks of life. Molecular beam/surface scattering experiments provide a controlled environment for modeling abiotic processes at the interface of lytho- and atmosphere. Specifically, it has been proposed that exposed rock surfaces may have played a role in modifying activated atmospheric molecules in the presence of UV radiation toward the building blocks of life. We have found that extended exposure of pyrite mineral surfaces to hydrogen atoms creates a reduced iron surface. The reduced state and the modified geometric structure of the surface iron atoms were confirmed by X-ray spectroscopy. Furthermore, this modified pyrite surface shows remarkable chemical reactivity in converting the hyperthermal beam of N₂ to ammonia. Using biological examples such as nitrogen fixation by nitrogenase, hydrogen evolution and uptake by hydrogenases, and reversible CO/CO₂ conversion by CO dehydrogenase, we began to study the effect of heterometal (Mo, V, Ni) substitution in iron-sulfur minerals and particles. We have successfully bound molybdenum sulfide on pyrite mineral surfaces and exploring the synthetic feasibility of doping Ni into freshly precipitated FeS particles. Preliminary reactivity studies indicated higher yields in formation of ammonia from nitrogen oxides at hydrothermal conditions relative to the pure iron-sulfur systems.

Origin of Life Philosophy Discussion Group

The ABRC philosophy group is going into its fourth year and with it is undergoing a changing of the guard. Moving on from the group are biochemistry graduate student graduate student Shawn McGlynn, undergraduate physics and philosophy major Nathan Haydon, and undergraduate philosophy major Olin Robus who really set the stage for the first generation of the group advised by MSU Regents Professor Gordon Brittan and Philosophy Professor Prasanta Bandyopadhyay, This group focused on more metaphysical issues and worked together on the role of quantum mechanics and potential quantum decoherence in the evolution of the evolution of catalysts. New group member Trevor Beard teamed up with McGlynn at the recent 2010 AbSciCon meeting to present a poster evaluating “Metabolism First” and “RNA World” theories for the Orign of Life from both scientific and philosophical perspectives. The group has spoken at our monthly team videoconferences on a number of occasions and the perspective the group provides increases the entire groups breadth and appreciation of the tremendous complexity of the Origin of Life as a scientific problem. In the coming year with the addition of Philosophy Professors with expertise in intelligence (Sara Waller) and social impacts and ethics (Kristin Intemann), the group will expand the issues addressed.

Education and Public Outreach

ABRC created a visitors’ guide to Yellowstone called “Science of the Springs” that explains the astrobiology research happening in Yellowstone, using innovative cell phone technologies to meld print and electronic information, QR codes with in the guide can be scanned and will direct the user to selected websites. ABRC has created an Alien Night party for libraries in Montana. Alien Night is a dynamic family event designed to teach the public about astrobiology and the research happening in Montana. ABRC is a primary sponsor of MSU Science Zone, a monthly science column that is distributed to 50,000 K-5 students and teachers via Kidsville News, a national publication with a regional Montana edition. About 120 K-12 teachers and education majors celebrated the 50th anniversary of exo/astrobiology at Montana State University’s second-annual Teacher Resource Fair on Oct. 13, 2010. This years Community lecture series featured Dr. David DeMarias of NASA Ames, he presented “Exploring Mars for Evidence of Habitable Environments and Life.” This lecture was free and open to the public. The Astrobiology team at Montana State University, in conjunction with NTEN at MSU, is developing “Introduction to Elementary Astrobiology,” an online short course with modules addressing astrobiology subject material. The course modules provide building blocks to allow participants to contemplate and investigate the potential for finding life beyond Earth. The online short course is a self-paced course with interactive components as well as links to NASA resources.

An Undergraduate Curriculum in Astrobiology at Montana State University

This year our new Minor in Astrobiology at Montana State University was approved by the Montana State Board of Regents and is available for the first time fall 2010. This 30 credit minor includes coursework in Astronomy, Biology, Chemistry, Ecology, Earth Science, and Microbiology and two new courses in Astrobiology. The first gateway or introductory course was offered this fall (Fall 2010) and sets the stage in defining the major questions in Astrobiology and the progress that has been made in the field to date. The capstone course for the minor is in the later stages of development and will be offered during the next academic year and will be a Junior/Senior Astrobiology Science course that will include a communicating to public audiences practicum. We are currently working with Montana State University Extended University to make both these courses available as on line courses so other campuses might be able to offer Astrobiology Minors as part of their curriculum without further course development.