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Research Description:
My research explores habitats for life in permanently frozen environments, with
the ultimate objective of characterizing the ecological, physiological, and
molecular adaptations that enhance microbial survival under such extreme frozen
conditions. Although glaciated environments have been traditionally viewed as
being devoid of life, recent information indicates that the surface, basal zone,
and subsurface of glaciers (e.g., subglacial lakes) contain unique microbial
ecosystems that operate at or below the freezing point of water. Short descriptions
of my active research areas appear below:
More details on my research can be found at http://brent.xner.net
(i) Microbiology and biogeochemistry of glacial ice. Archived chronologically within glaciers are samples of the atmospheric constituents from different times in the past, including biological material such as insects, plant fragments, seeds, pollen grains, spores, viruses, and bacteria. Numerous studies attest to the presence of viable bacteria in ice cores hundreds of thousands of years old. Perhaps the bacteria possess molecular and physiological adaptations that enhance their survival under nongrowth conditions (e.g., enhanced DNA repair), but it is also possible that cells carry out a slow rate of metabolism in the ice to offset macromolecular damage (e.g., to DNA). Theoretical work argues that solute-rich liquid veins between adjacent ice crystals may provide a habitat for active metabolism in glacier ice. Confirming this would support the view that the World’s glaciers and ice sheets are active biomes, significantly expanding the known boundaries of the biosphere (>70% of the freshwater and ~10% of Earth’s surface is glacial ice). To this end, a combination of laboratory and field studies are underway to examine the ability of microorganisms to metabolize and respire CO2 in the liquid fraction of ice at temperatures from -5 to -20oC.
(ii) Limnology of subglacial lakes. More than 140 subglacial lakes have been identified thus far under Antarctica’s expansive ice cover. The largest of these lakes, subglacial Lake Vostok (>14,000 km2), is located ~4 km beneath the surface of the East Antarctic ice sheet and has been isolated from the atmosphere for at least 15 million years. Lake Vostok has not yet been directly sampled; however, an ice core has been retrieved in which the bottom ~85 meters consists of lake water that has accreted to the bottom of the ice sheet. Biogeochemical analysis of the accreted ice infers that the shallow coastlines of the lake may be more biologically active, relative to surface waters over deeper portions of Lake Vostok. While the exact nature of this environment remains unknown, the data support the working hypothesis that a sustained ecosystem exists in Lake Vostok despite high pressure, constant cold, low nutrient input, potentially high O2 concentrations, and an absence of sunlight. The accreted ice provides important data for predicting limnological conditions in Lake Vostok, and subglacial lakes in general, allowing meaningful experiments to be designed when subglacial lakes are eventually sampled, which should be within the next few years.
(iii) Microbiological meteorology: biological ice
nucleation and precipitation. Certain plant-associated bacteria 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. Ice nucleating
active bacteria are present at altitudes of several kilometers and have been
documented in rain and snowfall. Based on the warm temperature and efficiency
at which they function as ice nuclei, we hypothesize that these biotic particles
have important impacts on atmospheric processes by serving as freezing catalysts
in clouds, thus inducing precipitation. Glacier ice cores provide long-term
records to examine linkages between airborne biological ice nucleating particles,
environmental conditions, and precipitation.
Christner, B.C., G. Royston-Bishop, C.F. Foreman, B.R. Arnold, M. Tranter, K.A. Welch, W. B. Lyons, A.I. Tsapin, M. Studinger, and J.C. Priscu. 2006. Limnological conditions in subglacial Lake Vostok, Antarctica. Limnology and Oceanography, 51:2485-2501.
Christner, B.C., J.A. Mikucki, C.M. Foreman, J. Denson, and J.C. Priscu. 2005. Glacial ice cores: a model system for developing extraterrestrial decontamination protocols. Icarus, 174:572-584.
Christner, B.C., E. Mosley-Thompson, L.G. Thompson, and J.N. Reeve. 2005. Recovery and identification of bacteria from polar and non-polar glacial ice. In S. O. Rogers and J. Castello (eds), Life in Ancient Ice, pp. 209-227. Princeton University Press, Princeton, New Jersey.
Royston-Bishop, G., J.C. Priscu, M. Tranter, B.C. Christner, M.J. Siegert, and V. Lee. 2005. Incorporation of particulates into accreted ice above Subglacial Lake Vostok, Antarctica. Annals of Glaciology 40:145-150.
Priscu, J.C., and B.C. Christner. 2004. Earth’s icy biosphere. In Bull, Alan T. (ed.), Microbial Diversity and Bioprospecting, pp. 130-145. American Society for Microbiology, Washington, D.C.
Christner, B.C., B.H. Kvitko, and J.N. Reeve. 2003. Molecular identification of bacteria and eukarya inhabiting an Antarctic cryoconite hole. Extremophiles, 7:177-183.
Christner, B.C., E. Mosley-Thompson, L.G. Thompson, and J.N. Reeve. 2003. Bacterial recovery from ancient ice. Environmental Microbiology 5:433-436.
Christner, B.C. 2002. Incorporation of DNA and protein precursors into macromolecules by bacteria at -15oC. Applied and Environmental Microbiology 68:6435-6438.
Christner, B.C., E. Mosley-Thompson, L.G. Thompson, and J.N. Reeve. 2001. Isolation of bacteria and 16S rDNAs from Lake Vostok accretion ice. Environmental Microbiology 3:570-577.
Christner, B.C., E. Mosley-Thompson, L.G. Thompson, V. Zagorodnow, K. Sandman, and J.N. Reeve. 2000. Recovery and identification of viable bacteria immured in glacial ice. Icarus 144:479-485.