Current Research in the Christner Laboratory:

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

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 CO₂ in 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

ICIBASE tunnellers: Top - Timothy Brox, Scott Montross, and Shawn Doyle. Bottom - Pierre Amato and Brent Christner.

B-236 2009-10:  Top - Scott Montross, Brent Christner, Amanda Achberger, and Timothy Brox. Bottom - Lindsay Knippenberg, Shawn Doyle, and Mark Skidmore.

Microbial Activity in Solid Ice: Implications for Modifying the CO₂ Record in Ice Cores 
Recent studies of microbial longevity in ancient glacial ice indicate that bacteria remain viable for hundreds of thousands of years while frozen. In the absence of metabolic activity, macromolecular damage must accumulate through amino acid racemization, DNA depurination, and exposure to natural ionizing radiation (e.g., ⁴⁰K). Perhaps the species recovered are particularly successful at surviving metabolic dormancy over extended time frames, but it is also possible that such entrapped microbes might carry out a slow rate of metabolism to repair incurred macromolecular damage. We are examining the ability of bacteria isolated from glaciated environments to metabolize and respire CO₂ in the liquid fraction of artificially constructed ice matrices. Experiments are underway to examine the influence of temperature and unfrozen water chemistry on microbial activity under frozen conditions. In addition, we are also studying the physiology of cells entrapped in ice by quantifying the fraction of viable and respiring cells and characterizing the genes and proteins expressed under frozen conditions. The presence of microbes within the aqueous fraction of the ice is fundamental to our research hypotheses, and we are using light and scanning electron microscopic analysis of the ice to determine the partitioning of both cells (visually) and solutes (elemental mapping) between the veins and the ice matrix. Importantly, the proposed research represents the first attempt to measure microbial CO₂ respiration and macromolecular synthesis under environmental conditions (–5 to -20°C) in which elevated CO₂ concentrations have been reported in glacial ice cores and basal ice from cold based glaciers.
Funding: National Science Foundation, Research in Biogeosciences

High Altitude BIological Testing of the ATmosphere (HABITAT): Developing a Sampling Platform to Measure the Upper Boundaries of the Biosphere  
We propose to design, fabricate, integrate and field test, in a series of demanding and scientifically important laboratory and field exploration operations, the next-generation in instruments for biological sampling of the troposphere and stratosphere. Our new sampling platform ― HABITAT (High Altitude BIological Testing of the ATmosphere) ― will break new ground on several major fronts, including spatial detection and quantification of the concentration, nature, and viability of biological particles with height in the atmosphere. Due to the similarity of conditions, studying life in the Earth’s atmosphere provides a window into the possibility and nature of life which may exist in extraterrestrial systems. The experiments we propose are conceptually very simple, and technically require only routine microbiological procedures; however, several key technical advances are required to meet the extreme challenges associated with the collection of cells in the high atmosphere, which we expect to be sparsely distributed. The success of HABITAT will make significant strides towards enabling flagship level missions to planets and moons in our solar system by proving out a number of relevant technologies in an integrated test series that is representative of the temperature, pressure, and radiation conditions expected in many extraterrestrial environments. If fully successful, HABITAT may enable analysis and sample return from the atmospheres and surfaces of extraterrestrial planets or moons (e.g., Mars, Jupiter, Venus, and Titan).
Funding: LaSPACE

Biological Ice Nuclei: is There a Bioprecipitation Cycle?  
Several species of plant-associated bacteria are known to have the capacity to freeze supercooled water at temperatures as warm as -1° C, which is catalyzed by a protein in the outer membrane of the bacterial cell. Due to the relatively warm temperatures at which ice-nucleating bacteria can function as freeze catalysts, these particles may impact meteorological processes by inducing precipitation (i.e., natural cloud seeding). The heterogeneous nucleation of supercooled water in clouds initiates ice crystal formation, and when the crystals become large enough, the particles precipitate out forming snow or rain. We are currently examining the distribution of biogenic ice nuclei in precipitation deposited under known environmental conditions from Louisiana, Montana, Wyoming, France, the Arctic, and Antarctica. Snowfall accumulated over long periods and transformed into glacier ice records samples of the atmospheric constituents in a chronological sequence. Through analysis of ice core samples, the occurrence of biogenic ice nuclei from known times and environmental conditions in the past can be examined. This study represents the first attempt to examine a direct link between atmospheric biogenic ice nuclei and the hydrological cycle.
Funding: Louisiana State University, Office of Research and Economic Development