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Current Research in the Christner
Laboratory:
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
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, Office of Polar Programs

ICIBASE tunnellers: Top (l-r) Timothy Brox, Scott Montross, and
Shawn Doyle. Bottom (l-r) Pierre Amato and Brent Christner.
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
Collaborations:
L. DeWayne Cecil (United States
Geological Survey)
Christine Foreman (Montana State University)
Cindy Morris (Institut National de la Recerche Agronomique, France)
John Priscu (Montana State University)
James Raymond (University of Nevada at Las Vegas)
David Sands (Montana State University)
Stephan Schuster (Pennsylvania State University)
Mark Skidmore (Montana State University)
Todd Sowers (Pennsylvania State University)
Jean-Louis Tison (Free University, Belgium)
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