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2011 Annual Science Report

Pennsylvania State University Reporting  |  SEP 2010 – AUG 2011

Executive Summary

Through an integration of education and research, the Penn State Astrobiology Research Center (PSARC) is dedicated to developing the conceptual, analytical, and technical tools to detect life, extant or extinct. This past year has been a great one for PSARC researchers. Each of our four major research projects had splendid results, novel directions, and new important papers. For example, our developing new biosignatures project produced 17 peer-reviewed papers, including multiple papers in the Proceedings of the National Academy of Sciences. Below are highlights from each of our four research projects.

Developing New Biosignatures

The development and experimental testing of potential indicators of life is essential for providing a critical scientific basis for the exploration of life in the cosmos. In microbial cultures, potential new biosignatures can be found among isotopic ratios, elemental compositions, and chemical changes to the growth media. Additionally, life can be detected and investigated in natural systems by directing cutting-edge instrumentation towards the investigation of microbial cells, microbial fossils, and microbial geochemical products. This interdisciplinary research brings to methods to the field of astrobiology for investigating microbial life. This past year, we have applied optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy to Miocene and Permian sulfates, apatite-biomineralized protists, and chert-permineralized Paleoproterozoic sulfuetum. In each case, our advanced methods have revealed ancient microfossils with great sensitivity and in remarkable detail. We have also continued to look at weather of rock material as a recorder of past climate conditions and biological activity. Freeman and her research group have developed Scytonemin and F430 as new biomarker targets for astrobiological studies. We were part of a group lead by NASA Goddard to report purine diversity in primitive meteorites. We continued to develop DNA and metagenomics as method for astrobiology with a paper on deep sea sediment of the Gulf of Mexico and new expeditions to Costa Rica and Okinawa. Finally, we initiation our Citizen Science Project on thermophiles in domestic water heaters.

Biosignatures in Mission Relevant Environments

PSARC is investigating microbial life in some of Earth’s most mission-relevant ecosystems. These environments include the Dead Sea, the Chesapeake Bay impact structure, Eel River Basin methane seeps, Greenland glacier ice, and redox-stratified precambrian ocean analog sites. PSARC is targeting environments that, when studied, provide fundamental information that can serve as the basis for future solar system exploration. Combining our expertise in molecular biology, geochemistry, microbiology, and metagenomics, we are deciphering the microbiology, fossilization processes, and recoverable biosignatures from these mission-relevant environments.

Graduate students Moshe Rhodes and Katherine Dawson (House, Macalady, Freeman) published papers that reveal the unique attributes of hypersaline environments such as the Dead Sea with respect to lateral gene transfer, amino acid signatures, and membrane lipid biomarkers. Rhodes’ work revealed that while hot springs tend to degrade exotic DNA, hypersaline environments may preserve genetic material available for lateral gene transfer from a wide range of other sources. Dawson’s work showed that the degree of membrane lipid unsaturation is an important adaptation to specific salinity niches in archaeal halophiles.

Team members at Caltech (Orphan) and Penn State (House) working on marine methane seeps provided additional evidence that carbonates and silica-rich minerals forming as a result of anaerobic oxidation of methane (AOM) entomb and record the associated microbial diversity. These results are important because the ability to differentiate between cellular remains and acellular mineral matter is critical for life detection efforts on other planets, as well as for tracking the evolution of biogeochemical cycles on Earth. They also probed the likely interactions between methane oxidation and sulfate and metal oxidants in the earth system through time.

The Brenchley laboratory and colleagues continue to develop new decontamination, authentication, and microbial cultivation strategies that allow investigation of microorganisms preserved deep within ice sheets. Their research is expanding our knowledge of the diversity and physiology of microbial cells trapped in ice.

Work completed by Astrobiology Dual Title Ph.D. student Rebecca McCauley (Macalady) showed that anoxic cave lake waters ~600 m below ground surface harbor unexpected diversity and a large percentage of uncultivated microbial taxa likely engaged in sulfur cycling.

A new collaboration has been launched between PSARC investigators (Macalady, Kump, Freeman) and MIT (Summons, Newman) to study genetic and environmental controls on hydrocarbon biomarker production in precambrian ocean analog environments.

Biosignatures in Ancient Rocks

The Earth’s Archean and Proterozoic eons offer the best opportunity for investigating a microbial world, such as might be found elsewhere in the cosmos. The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Researchers have recognized a variety of mineralogical and geochemical characteristics in ancient rocks (sedimentary and igneous rocks; paleosols) that may be used as indicators of: (i) specific types of organisms that lived in the oceans, lakes and on land, and (ii) their environmental conditions (e.g., climate; atmospheric and oceanic chemistry). These possible “biosignatures” include: (a) microfossils and stromatolites; (b) molecular structures (biomarkers) and isotopic compositions of C, N, and H in organic matter; (c) multiple S and O isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements). As part of our integrated plan, we will study geochemical, isotopic, and sedimentary signatures of life in order to understand the context in which these biosignatures formed. Ultimately, we will use biosignatures in conjunction with evolutionary genomics to reveal the early history of metabolism and understand the interplay between life, oceans, and atmospheres during these early eons.

Our research on biosignatures in ancient rocks includes efforts to understand sulfur isotopic signatures recorded in ancient rocks. For example, Dr. Watanabe and Mr. Andrew Choney (Research Assistant) have been conducting TSR experiments using a variety of solid organic compounds (e.g., mixtures of alanine and glycine; dried cyanobacteria; extracted kerogen from young sediments). They have recognized that the mixtures of two amino acids (alanine and glycine) generated H2S with Δ33S values as large as +2.3‰ and Δ36S values ranging from -1 to +1. 5‰; these values are larger than those produced by alanine or glycine alone. This suggests the TSR with multiple organic compounds may generate larger Δ33S values.

This past year Kump, Arthur, Junium and Luo discovered a massive oxidation event at what is traditionally considered the end of the “Great Oxidation Event”, about 2.0 billion years ago. The evidence is a very large, negative carbon isotope excursion preserved in both organic matter and carbonates from Fennoscandia (in FAR-DEEP drill core) and also, strikingly, in Gabon, Africa. The required input of oxidized organic matter (presumably from sedimentary rock weathering) is huge, perhaps reflecting the initial, deep penetration of highly oxidizing groundwaters in Earth history (Kump et al., Science, in review).

Also, during this past year, Kasting’s group determined that the combined greenhouse effect of CH4 and N2O could have provided up to 10 degrees of warming, thereby keeping the surface warm during the Proterozoic without necessitating high CO2 levels.

Biosignatures in Extraterrestrial Environments

Efforts to detect and characterize life will occur in extraterrestrial settings during remote solar system exploration and through observations of extrasolar planets. Sigurdsson and collaborators in the Center for Exoplanets and Habitable Worlds continued research on extrasolar planets: graduate student Rachel Worth commenced project on radial transport in the solar system in collaboration with Sigurdsson and House. Pathfinder near infrared spectrograph operated at HET telescope, U-Ne calibration for near IR and implementation of NIST supplied lasercomb operated and cross-calibrated. In part due to support from NAI to demonstrate the feasibility of this technique, the NSF awarded a Major Reseach Instrumentation grant in 2011 to build a facility class Planetfinder spectrograph (PI Mahadevan). Graduate student Matthew Route, in collaboration with Professor Wolszczan, did radio observations to find sub-stellar companions to nearby stars, and graduate student Sara Gettel continued long term monitoring of bright giant stars, looking for long period exoplanets. Professor Wright continued ongoing observations of exoplanets and looking for new exoplanets, using radial velocity monitoring, and started a new project on early Solar System formation. Professor Wright continued work on the Exoplanets catalog Graduate student Rachel Worth started modeling of transport of meteorite ejecta in the Solar System in collaboration with Profs House and Sigurdsson, using NAI Hawaii computing facilities. Research on early Solar System dynamical evolution continued.