2011 Annual Science Report
Astrobiology Roadmap Objective 3.4 Reports Reporting | SEP 2010 – AUG 2011
The central theme of this project is to explore the possible connections between chemistry in space and the origins of life. We start by tracking the formation and development of chemical complexity in space from simple molecules such as formaldehyde to complex species including amino and nucleic acids. The work focuses on molecular species that are interesting from a biogenic perspective and on understanding their possible roles in the origin of life on habitable worlds. We do this by measuring the spectra and chemistry of analog materials in the laboratory, by remote sensing in small spacecraft and by analysis of extraterrestrial samples returned by spacecraft or that fall to Earth as meteorites. We then use these results to interpret astronomical observations made with ground-based and orbiting telescopes.ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.1 3.2 3.4 4.3 7.1 7.2
BioInspired Mimetic Cluster Synthesis: Bridging the Structure and Reactivity of Biotic and Abiotic Iron-Sulfur Motifs
Bioinspired synthetic approaches are being utilized to bridge the gap between Fe-S minerals and highly evolved biological Fe-S metalloenzymes. Biology builds complex Fe-S clusters by first synthesizing standard Fe-S clusters and then modifying them through radical chemistry catalyzed by radical SAM enzymes. In an effort to examine hypothetical early biocatalysts, we probing simple Fe-S motifs capable of coordinating Fe-S clusters in aqueous solutions that can initiate radical chemistry.ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2
We have analyzed over four thousand astrobiology articles from the scientific press, published over ten years to search for clues about their underlying connections. This information can be used to build tools and technologies that guide scientists quickly across vast, interdisciplinary libraries towards the diverse works of most relevance to them.ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 3.2 3.3 3.4 4.1 4.2 4.3 5.1 5.2 5.3 6.1 6.2 7.1 7.2
Ecology of Extreme Environments: Characterization of Energy Flow, Bioenergetics, and Biodiversity in Early Earth Analog Ecosystems
The distribution of organisms and their metabolic functions on Earth is rooted, at least in part, to the numerous adaptive radiations that have resulted in the ability to occupy new ecological niches through evolutionary time. Such responses are recorded in extant organismal geographic distribution patterns (e.g., habitat range), as well as in the genetic record of organisms. The extreme variation in the geochemical composition of present day hydrothermal environments is likely to encompass many of those that were present on early Earth, when key metabolic processes are thought to have evolved. Environments such Yellowstone National Park (YNP), Wyoming harbor >12,000 geothermal features that vary widely in temperature and geochemical composition. Such environments provide a field laboratory for examining the tendency for guilds of organisms to inhabit particular ecological niches and to define the range of geochemical conditions tolerated by that functional guild (i.e., habitat range or zone of habitability). In this aim, we are examining the distribution and diversity of genes that encode for target metalloproteins in YNP environments that harbor geochemical properties that are thought to be similar to those that characterize early Earth. Using a number of newly developed computational approaches, we have been able to deduce the primary environmental parameters that constrain the distribution of a number of functional processes and which underpin their diversity. Such information is central to constraining the parameter space of environment types that are likely to have facilitated the emergence of these metal-based biocatalysts.ROADMAP OBJECTIVES: 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3
Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface. Habitability of Icy Worlds investigation has three major objectives. Objective 1, Seafloor Processes, explores conditions that might be conducive to originating and supporting life in icy world interiors. Objective 2, Ocean Processes, investigates the formation of prebiotic cell membranes under simulated deep-ocean conditions, and Objective 3, Ice Shell Processes, investigates astrobiological aspects of ice shell evolution.ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.1 3.2 3.3 3.4 4.1 5.1 5.3 6.1 6.2 7.1 7.2
We have through NAI Director’s discretionary initiated a project to probing the structural determinants for nickel-iron-sulfur based reversible carbon monoxide oxidation. We are probing whether we can mimic the reactivity of carbon monoxide dehydrogenase to some extent by simple organic nesting and synthesis of nickel-iron-sulfur clusters using a model system we have developed.ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2
The main goal of this project is to identify critical requirements for the emergence of biological complexity in early habitable environments by examining key steps in the origins and early evolution of functional proteins and metabolic reaction networks. In particular, we investigate whether protein functionality can arise from an inventory of polymers with amino acid sequences that might have naturally existed in habitable environments. We attempt the first demonstration of multiple origins of a single enzymatic function, and investigate experimentally how primordial proteins could evolve through the diversification of their structure and function. Building on this work and on our knowledge of ubiquitous proto-cellular functions and constraints of prebiotic chemistry, we conduct computer simulations aimed at elucidating fundamental principles that govern coupled evolution of early metabolic reactions and their catalysts, and transport across cell walls.ROADMAP OBJECTIVES: 3.2 3.4
Metal oxides have been studied widely in the biogeochemical literature for understanding the adsorption and other surface interactions of dissolved organic and inorganic molecules with mineral surfaces. The goal of our study is to understand whether the earliest lipid membranes or “protocells” would have been stable in contact with different mineral surfaces on early Earth, and whether the surface properties of the minerals control their relative affinity to cell membranes. In previous years of this study, we used bulk adsorption isotherms and classical DLVO theory modeling approaches to examine the stability lipid bilayers in contact with micron-sized quartz (α-SiO2), rutile (α-TiO2) and corundum (α-Al2O3) particles. By understanding the role of natural geochemical parameters such as mineral surface chemistry, solution chemistry and temperature cycling on protocell membrane stability, we attempted to model potential aqueous environments where life may have originated such as lacustrine, tidal pool, and sub-aerial or submarine hydrothermal vents. In the present project year, we used neutron reflectivity to determine if the geometry of the mineral surface (sub-spherical particles versus planar single crystal surfaces) affects membrane stability. The results of our various approaches were consistent showing that lipid membrane stability depends on (1) lipid head-group charge and (2) surface charge of the mineral, which in turn depend on pH, ionic strength, presence or absence of Ca2+, (3) van der Waals interactions, and (4) relative hydrophobicity of the surface, as well as purely physical parameters such as relative size of the model membrane relative to the mineral surface. Our project addresses NASA Astrobiology Institute’s (NAI) Roadmap goals of understanding the origins of cellularity and the evolution of mechanisms for survival at environmental limits, and NASA’s Strategic Goal of advancing scientific knowledge of the origin and evolution of the Earth’s biosphere and the potential for life elsewhere.
Keywords: lipid, protocell, vesicle, self-assembly, pre-biotic, mineral surface, hydrophilic, hydrophobic, bilayerROADMAP OBJECTIVES: 3.4 5.1
Project 2C: Role of Extracellular Polymeric Substances (EPS) and Bacteria Cell Wall Structure in Shielding Against Specific Mineral Toxicity – Implications for Cell Surface Evolution
Our interdisciplinary project examined the hypotheses that (1) bacterial cell membranes are ruptured in contact with specific mineral surfaces, (2) biofilm-forming extra-cellular polymeric substances (EPS) may have evolved to shield against membrane rupture (cell lysis), (3) differences in cell-wall structure of Gram-negative and Gram-positive bacteria may influence the susceptibility of cells to toxic minerals and (4) mineral toxicity depends on its surface chemistry and nanoparticle size.
Previously, we have examined Gram-negative P. aeruginosa strains, wild-type (PAO1) that is capable of generating copious amount of EPS and producing biofilms, as well as the knock-out mutant (Δ-psl) that is defective in its ability to form EPS and biofilms. In the 2010-2011 year of funding, we have expanded our study to include Gram-positive B. subtilis strains, biofilm-producing wild-type NCIB3610 and biofilm-defective mutant yhxBΔ. We confirmed the hypotheses (1), (2) and (4) for both Gram-negative and Gram-positive bacteria, with toxicity increasing as amorphous β-TiO2 < γ-Al2O3. We also confirmed hypothesis (3) that Gram-positive bacteria are less susceptible to mineral toxicity than Gram-negative because of the most robust cell-wall structure of the former. Finally, we have shown that the mechanisms of toxicity depends on mineral surface charge for initial adhesion of nanoparticles to the cell surface, nanoparticle size which determines whether the particles can enter the intracellular space (e.g., for γ-Al2O3), the presence of surface free radicals (e.g., β-TiO2 ) which would have been generated by UV-radiation and meteorite impacts on early Earth, Mars, and other worlds.
By understanding the mechanisms for membranolysis, especially under the extreme conditions of high radiation and heavy impacts during early planetary history, the project addresses the NASA Astrobiology Institute’s (NAI) Roadmap goals of understanding the origins of cellularity, the evolution of mechanisms for survival at environmental limits, and preservation of biosignatures, and NASA’s Strategic Goal of advancing scientific knowledge of the origin and evolution of the Earth’s biosphere and the potential for life elsewhere.ROADMAP OBJECTIVES: 3.4 5.1 7.1