Christner Research Group

Why Study Life in the Cold?

Despite the fact that >80% of the biosphere (by volume) is permanently below 5°C and most of the biomass is microbial, very little is known about the biology of microorganisms inhabiting permanently cold environments. Our research efforts are contributing to fill this knowledge gap through laboratory- and field-based projects aimed at understanding the nature and biogeochemical contributions of microbial life in environments beneath polar ice sheets and in the high atmosphere.

Current Research Projects:

GeomicroBiology of Antarctic Subglacial Environments (GBASE) Beneath the Whillans Ice Stream

The GBASE project is one of three research components of the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) integrative initiative that is being funded by the Antarctic Integrated System Science Program of NSF's Office of Polar Programs, Antarctic Division. The overarching scientific objective of WISSARD is to assess the role of water beneath a West Antarctic ice stream in interlinked glaciological, geological, microbiological, geochemical, and oceanographic systems. GBASE will examine distinct, but hydrologically related, subglacial environments using a combination of biogeochemical/ genomic measurements to answer key questions directly relevant to metabolic and phylogenetic biodiversity, and the biogeochemical transformation of major nutrients beneath the Whillans Ice Stream. We expect the microbial communities associated with the ice stream to be a metabolically dynamic ecosystem, and specifically ask (1) what is the microbial community structure and (2) what is the metabolic function of the community in situ? Understanding biogeochemical processes involved with elemental transformations on our planet is a central theme in NSF's decadal plan and the use of multidisciplinary tools to study these transformations in polar regions has been recommended by a 2007 NRC report that states "It is time for scientific research on subglacial lakes to begin". GBASE results will be used by investigators of LISSARD and RAGES (the other two components of the WISSARD project) to cast their results in a holistic ecosystem perspective.
Funding: National Science Foundation, Antarctic Integrated System Science

Greenland melt water Geomicrobiology

The Greenland Ice Sheet (GrIS) is the largest freshwater reservoir in the Arctic. Melting of the GrIS is increasing, delivering large amounts of freshwater to the Arctic Ocean. The nature and composition of microbial communities below the GrIS are not known, but recent studies have documented the presence of viable microbial communities in other subglacial environments and within the GrIS ice itself, indicating their potential importance for chemical weathering processes. This collaborative project will characterize GrIS subglacial microbial communities to investigate the effect of microbes on lithospheric weathering and nutrient fluxes from the GrIS margin in West Greenland. The hypothesis is that the glacial thermal regime and bedrock lithology are the primary determinants of the subglacial bacterial communities, which in turn mediate nutrient release and weathering rates. Study sites in the Thule and Kangerlusuaq areas cover two major lithologies of West Greenland. The study combines state-of-the art microbiological, biogeochemical techniques, and datalogging of stream and climate parameters, to examine glacial meltwater. Information on the chemical composition and fluxes of meltwater (particularly carbon, iron and trace nutrients) and sediments released by the GrIS will provide fundamental data towards a conceptual model of GrIS subglacial microbial environments.
Funding: National Science Foundation, Arctic Sciences Division

DNA Repair Under Frozen Conditions: Implications for the Longevity of Microorganisms in Terrestrial and Extraterrestrial Ices

Ambient levels of natural ionizing radiation are of little consequence to microorganisms inhabiting most environments on Earth. However, in the absence of metabolic activity over a prolonged timeframe, a dormant microorganism would eventually receive a dosage beyond which effective repair is no longer possible. Microbiological investigations of ancient glacier ice and permafrost have documented viable bacteria in samples hundreds-of-thousands- to millions-of-years old. Recent laboratory studies have demonstrated that microorganisms remain metabolically active in the liquid fraction of ice matrices at temperatures as low as -20^oC, supporting the notion that some level of metabolism may occur in permanently frozen environments. The ability of cells to remain metabolic activity (e.g. to conduct DNA repair) in ice would allow viability for extended periods of time, and the longevity of microorganisms under frozen conditions may only be limited by the water activity and availability of energy and nutrient sources. The objectives of the proposed research are to: (1) examine the physiological and biochemical effect of sublethal levels of ionizing radiation on populations of ice-entrapped bacteria; (2) evaluate the ability of microorganisms to repair chromosomal damage sustained from ionizing radiation under frozen conditions; (3) establish the rate of macromolecular synthesis under frozen conditions that is required to effectively repair cellular damage resulting from single- and double-stranded DNA breakage and protein oxidation; and (4) improve predictions for the radiation-dependent limit for microbial longevity in terrestrial and extraterrestrial ices. This study will examine biological repair mechanisms at temperatures germane to those existing in icy extraterrestrial environments (e.g., the polar regions of Mars) and increase scientific knowledge on the metabolic capabilities of bacteria at subzero temperatures.
Funding: National Aeronautics and Space Administration, Astrobiology: Exobiology and Evolutionary Biology

Modes of Adaptation, Resistance, and Survival for Life Inhabiting a Freeze-dried-radiation-bathed Environment (MARSLIFE)

The presence of water on Mars and on a number of planetary moons (e.g., Europa, Enceladus, Ariel, and Triton) suggests that multiple loci within the solar system may plausibly support microbial life. The overarching theme of the project proposed here, MARSLIFE, is that selective pressures in terrestrial extreme environments serve as “training grounds” that enrich for microbial phenotypes that may dominate extraterrestrial habitats on Mars and elsewhere. The MARSLIFE program will: (i) investigate existing and novel microorganisms with tolerances to cold, desiccation, and radiation as models for astrobiology; (ii) use laboratory simulators to assess responses of selected extremophiles to temperature, pressure, and radiation conditions that exist in a range of extraterrestrial environments; (iii) characterize biological resistance mechanisms to freezing, desiccation, and radiation, and (iv) improve technologies for the detection and sampling of microorganisms under conditions similar to the surface of Mars. The expected outcomes include the development of fundamental astrobiological concepts and operational capabilities that would promote the success of future NASA-driven life detection missions, inform policies on planetary protection, and lay the foundation for a new space research enterprise in Louisiana. The institutions, LSU, SU and LaTech, bring together a variety of research and education capabilities and, in conjunction with NASA mentors, the relationships nurtured within MARSLIFE will produce technologically informed, interdisciplinary scientists, foster new technology and educational opportunities, and increase the collaboration between NASA and Louisiana.
Funding: National Aeronautics and Space Administration (Experimental Program to Stimulate Competitive Research; EPSCoR) and the Louisiana Board of Regents

Biogeochemistry and Geomicrobiology of Taylor Glacier Basal Ice

To examine if microorganisms are metabolically active in glacier ice, we are conducting a comprehensive assessment of the biogeochemistry and geomicrobiology of Taylor Glacier (McMurdo Dry Valleys, Antarctica) basal ice via a combination of field measurements and laboratory experiments. A key component of the study is the ability extract parallel large volume samples (~10 kg) for analysis of nutrients, gas composition, d¹³C-CO₂, cell density, metabolic activity, genomic DNA, and nucleotide ratios. Importantly, these large ice samples provide biomass (10⁶-10⁸ total cells) and CO₂in quantities ~100x greater than typically available using ice core materials, permitting experiments that are difficult or unfeasible with ice core archives, such as measuring the isotopic composition of CO₂, nucleic acid characterization, and parallel biogeochemical and microbiological analyses. Using this approach, we are able to connect nutrient availability, geochemical composition, and gas composition with microbial cell density, diversity and metabolic status in the basal ice sequence. Multi-sample analysis of the same ice facies is the best available method to understand the chemical and microbial process linkages in basal ice and the manner by which microbes may modify gas compositions in situ.
Funding: National Science Foundation, Antarctic Organisms and Ecosystems

VALKYRIE (Very-Deep Autonomous Laser-Powered Kilowatt-Class Yo-Yoing Robotic Ice Explorer)

This project builds upon the results of Phase 1 of the VALKYRIE cryobot project; Phase 2 will involve three field campaigns to test a sub-scale variant of VALKYRIE: two campaigns at the Matanuska Glacier (Alaska) and one in Greenland near Kangerlussuaq. VALKYRIE will penetrate a series of selected glaciers, beginning with ice depths of 10—50m in 2012 and proceeding to as much as 200m in 2013. VALKYRIE will be equipped with an astrobiology sensor suite and will make an autonomous decision to collect a wall core sample from within the ice column. This will allow for follow-up microbiology assays to confirm the success of the vehicle’s autonomous approach. Furthermore, the cryobot will deploy line sensors in the ice cap to provide a new method of long-term autonomous glacial monitoring. This work is leading to a full-scale, Phase 3 South Pole Lake cryobot sample return mission, which will act as a dress rehearsal for delivering a science payload to subsurface oceans on Europa and Enceladus, as well as deep investigations of the Martian ice cap.
Funding: National Aeronautics and Space Administration, Astrobiology Science and Technology for Exploring Planets (ASTEP)

Research Sponsors:

Past Grants:

High Altitude BIological Testing of the ATmosphere (HABITAT): Developing a Sampling Platform to Measure the Upper Boundaries of the Biosphere

Funding: LaSPACE, 2009-10

Microbial Activity in Solid Ice: Implications for Modifying the CO₂ Record in Ice Cores

Funding: National Science Foundation, Research in Biogeosciences, 2005-09

Biological Ice Nuclei: is There a Bioprecipitation Cycle?