2011 Annual Science Report
Montana State University Reporting | SEP 2010 – AUG 2011
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 relationships provide a framework for the research being conducted at the Astrobiology Biogeocatalysis Research Center (ABRC) 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.
ABRC Research Highlights
In this fourth year of support we can say resoundingly that we have shown that the iron-sulfur system is a tractable model to gain insights into the Origin of Life through an integrated top-down and bottom-up approach. In that regard we can point to key results from both the mineral and enzyme focus areas where we have been able better bridge the gap and better envision potential steps that link these two endpoints. For example, we have demonstrated in the mineral focus area that energy applied to iron-sulfur minerals facilitates modification of mineral surfaces in a manner that more closely resembles the structure and reactivity of iron-sulfur cluster active sites. In addition, our results from the enzyme thrust, we have demonstrated that complex iron-sulfur enzymes are assembled in steps that are very much in line with what has been proposed for the first steps in the interaction between minerals and organics as early as the Hadean. We have shown that iron-sulfur motifs in biology are synthesized and assembled by steps that resemble what has been described for prebiotic ligand accelerated catalysis and organic compound metal and metal cluster nesting. In addition, by comparison of our results with the results of the work in other laboratories, we have been able to show that the mechanisms are somewhat pervasive within certain classes of enzymes. Perhaps most notable is the involvement of SAM radical enzymes representing yet another example of the cooperative nature of elements of the “RNA World” and “Iron-Sulfur World” but now at the level of catalysis and not just oxidation-reduction cascades. These observations open up exciting new directions for the mineral thrust and are in line with our original premise in that the results of the enzyme focus area should inspire and direct the work conducted in the mineral focus area.
In our mineral thrust we have reported chemical reactions in the literature that model a subset of interfacial processes of the atmosphere, hydrosphere, and lithosphere that are relevant to the chemical evolution of the building blocks of life. 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 (NO2-), nitrate (NO3-), as well as nitric oxide (NO) can be converted to ammonia with faster kinetics than when the reactant is dissolved 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. Using theoretical approaches, we created an atomic scale molecular model for the reactive Fe-site on pyrite surface and used this model to aid the assignments of the intermediate species adsorbed on the pyrite surface. In parallel, molecular beam/surface scattering experiments provide a controlled environment for modeling abiotic processes at the interface of litho- and atmosphere. Specifically, we conducted experiments that model how exposed rock surfaces may have interacted with activated atmospheric molecules in the presence of UV radiation. Using atomic H beam as the simplest substrate, we found that extended exposure of pyrite mineral surfaces to hydrogen atoms creates a reduced iron-sulfur surface and evolves H2S. It is expected that using any other H-X type atmospheric species (H2O, CH4, H2CO, etc.) would result in a similar surface reactivity in addition to the formation of sulfur-derivatized X (SOx, CH3SH, CH3SCH3, etc.). The reduced electronic state and the modified geometric structure of the surface iron-sulfur layer were confirmed by X-ray absorption spectroscopy. Computational modeling suggests the formation of a previously unknown Fe2S phase from the well-known FeS2 phase. Extended hydrogen atom exposure converts the pyrite surface to metallic iron. Importantly, this modified pyrite surface shows remarkable chemical reactivity in converting the hyperthermal beam of N2 to ammonia. Control experiments with quartz, carbon, and even metallic Fe surfaces show practically negligible amount of ammonia formation relative to the reduced iron-sulfur surface. 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 adsorbed molybdenum sulfide on pyrite mineral surfaces to form what is believed to be a Fe-Mo-S cubane surface complex. The synthetic feasibility of doping Ni into freshly precipitated FeS particles also has been investigated. Reactivity studies have indicated that the presence of Mo leads to higher yields ammonia from nitrogen oxides at hydrothermal conditions relative to the pure iron-sulfur systems. Recent preliminary results suggest that the addition of Mo to pyrite also facilitates the activation of dinitrogen and formation of ammonium in the aqueous environment. Follow up spectroscopic and computational work are planned to provide the atomic scale understanding for the role of the heterometals in activation of small molecules toward more reactive and thus more attractive intermediates toward the building blocks of life.
We developed new approaches to more substantively relate our work on the biochemistry of iron-sulfur systems to evolution, ecology, and habitability. The two parallel research projects we have developed are in the area of molecular evolution and microbial ecology, the latter of which emphasizes biogeography and more specifically habitability. With regard to molecular evolution, the emphasis has been focused on iron-sulfur enzyme evolution. Here we have incorporated two new and innovative approaches into the more traditional tools utilized in this area of research which leverage our specific knowledge of genomic, enzyme structure / function, and biosynthetic aspects of these systems. The first innovative approach involves the interrogation of the evolutionary trajectory of structural and biosynthetic proteins with a focus on the genetic events (gene duplications and gene fusions) that gave rise to these enzyme systems. The second approach involves making direct connections between the evolutionary and geologic records to attach real time scales and specific time frames to the evolution of key metabolic processes including nitrogen fixation, hydrogen metabolism, and photosynthesis. As an example of our recent work is the idea that the evolutionary origin of the most abundant and common nitrogenase on Earth today, the Mo-nitrogenase, was limited by the availability of Mo on prior to the rise of oxygen. Since there are close evolutionary links between the structural proteins that comprise nitrogenase and the enzymes that are required to synthesize chlorophyll and bacteriochlorophyll, a direct molecular clock experiment could be accomplished. Given that homologs of genes involved in chlorophyll and bacteriochlorophyll biosynthesis are also required for oxygenic phototrophs, we were able to calibrate our calculations in time based on the time frame suggested by geologists for the advent of oxygenic photosynthesis. The other area of complementary research we have developed involves investigating the environmental parameters that constrain or limit the distribution of target genes as proxies for iron-sulfur enzyme catalyzed processes that are the emphasis of our work (hydrogen metabolism, nitrogen fixation, carbon monoxide metabolism, and anaerobic carbon dioxide fixation). In very simple terms we have been using traditional approaches in statistical microbial ecology to define the environmental underpinnings of these processes to get a better handle on the types of environments where the processes may have emerged. Importantly, our focus on spatial patterns in the distribution of target gene lineages as a function of environment has significant promise for informing our understanding of why these proteins evolved over geological time scales. We are currently working to set calibration points on these datasets for use in linking spatial patterns in biodiversity to temporal evolutionary events (e.g., ocean euxina, Mo bioavailability). On another level we are also interested in what geochemical conditions favors a given mode of metabolism or which favored the emergence of a target metabolim; this project is directly related to questions of habitability and NASA missions. Relating the distribution of a functional process within an evolutionary and environmental context puts us in a better position to hypothesize about the types of metabolism or the life processes that might be anticipated in a given environment, based solely on a suite of measured geochemical parameters.
Origin of Life Philosophy
The ABRC philosophy group is going into its fifth year and so has both lost and gained personnel. Leaving the group are biochemistry graduate students Trevor Beard and Alta Howells; joining the group are graduate student in history of science Michael Bertasso, undergraduate philosophy majors Cameron Beebe, Taylor Harring, and Sam Foulkes, and continuing members are philosophy Professors Kristen Intemann, Sara Waller, and Prasanta Bandyopadhyay, This group focuses on epistemic, metaphysical, and social/ethical issues in astrobiology. 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. The group explores a range of issues from potential ethical principles to be used in policies governing the creation of artificial life to the relationship between animal minds and methodologies for searching for intelligent extra-terrestrial life. A selected list of presentations (in progress toward publication) from the last 18 months that have emerged as a direct result of this interdisciplinary collaborative group follows: “Why Need a Model? The Debate over the Origin of Life Theories and a Lesson from Simpson’s Paradox” (Astrobiology Science Conference, League City, TX); “Philosophy and Astrobiology: A Reply to Hawking” (Palomar College Roundtable Symposium: Philosophy, Science and the Meaning of Life); “Philosophy of Human and Dolphin Minds: Methodological and Theoretical Differences” (invited paper at SUNY Oneonta); “Philosophical, Psychological and Ethological Approaches to the Search for Intelligence” (Astrobiology Science Conference, League City, TX); “Assessing Potential Environmental and Health Risks of Protocells: Why ‘Precaution’ May Not Be the Best Principle.” at ISSOL in Montpelier France, July 2011.
Education and Public Outreach
Each year, hundreds of K-12 teachers learn about astrobiology via online and week-long summer courses, as well as classroom visits and guest speakers. Summer courses, which include fieldwork in Yellowstone National Park, have attracted teachers from throughout the U.S., Brazil, Canada, Netherlands and Japan. In addition, ABRC researchers are routinely involved in providing guided tours for classes from other NAI institutions (e.g., University of Wisconsin Astrobiology group) as well as affiliated institutions (Princeton University). ABRC also supports three elementary schools in eastern Montana’s St. Labre School District by providing hands-on science days and curricula. St. Labre’s student enrollment is nearly 100% Native American from the Crow and Northern Cheyenne Reservations.
Thousands of copies of “Science of the Springs,” ABRC’s guidebook to astrobiology research in Yellowstone, have been distributed throughout the Greater Yellowstone Ecosystem, and to teachers throughout the U.S. and as far away as Australia. The guidebook was also disseminated through the Southwest Montana Astronomical Society’s “Stars Over Yellowstone” program.
ABRC created an astrobiology-themed family educational night for a NASA rural library project. The project has served 1,300 people, approximately 350 of whom are Native American. Participants said the program made them more interested in space science and that they learned more about NASA research in Montana. The materials have also been used by classroom teachers and at Georgia Tech’s summer astrobiology camp, the Museum of the Rockies and the Bozeman Salvation Army summer camp.
ABRC’s Community Lecture Series has become a staple in the community, often attracting hundreds of people to hear visiting speakers from universities and NASA centers. In Fall 2011, Dr. Robert M. Hazen of the Carnegie Institute of Washington spoke to a full house at the Museum of the Rockies. Lectures are also recorded as video podcasts.
Each year ABRC is a major sponsor of MSU’s Astronomy Day, which draws nearly 2,000 people from throughout the region. ABRC distributes NASA products, hosts hands-on activities, and answers questions about NASA’s search for life in the Universe. ABRC has also designed and participated in events such as afterschool science, school family science nights, and Science Olympiad events.
ABRC has partnered with MSU’s renowned Science and Natural History Filmmaking Program to create a documentary film that takes a personal look at several scientists working with the NASA Astrobiology Institute to understand the origin of life. Once the film is completed in late 2011, ABRC will work to have the program distributed via a national outlet such as National Geographic, the Discovery Channel or PBS.
ABRC scientists continue to strive to make connections to underserved communities and groups across Montana as well as in neighboring states in an attempt to attract younger students to scientific disciplines. This has included numerous field days in Yellowstone National Park with members of the Boy Scouts of America among other groups in Livingston, lunch-time discussions with local middle school students in Bozeman, as well as efforts to access local newspapers with literature in astrobiology research and this has been successfully implemented in both the Livingston Enterprise and the Bozeman Daily Chronicle.
An Undergraduate Curriculum in Astrobiology at Montana State University
This year we are offering for the first time our capstone course for our Astrobiology Minor. This course is a Junior/Senior level Astrobiology Science course that follows the structure of the Lunine “Astrobiology: A Multidisciplinary Approach” text. The course is split into two major sections 1) Origin of Life and 2) Habitability and Search for Life. The course involves weekly visits from NAI scientists giving talks on a combination of scientific approaches and key scientific results. The students have really responded to these outside lectures due in no small part to the participation by a number of great speakers from across the NAI. They have two primary assignments that follow each of the two major sections described above 1) they are charged with writing a hypothesis paper on some sort of unifying Origin of Life theory where they bring in what they feel are the most compelling and value added elements of the current theories and 2) as a final project they will write a proposal for a NASA mission. As a unique component of this course, students are participating in an additional practicum called “Communicating Astrobiology to the Public.” The communications content dovetails with both science topics from the course as well as current events in astrobiology as students practice communications skills in science writing, graphic design, photography, Web sites and digital tools, radio, film, and more. Ideas developed by the students are incorporated into current E/PO strategies, and work produced by the students—such as kit activities, posters and more—will be available to the larger astrobiology community. The objective of the course and communications practicum are to train future scientists in how to both develop new ideas in astrobiology research and obtain the skills to communicate those concepts to the public.