Research Description: Laboratory and field research in the Christner Research Group is aimed at examining the molecular biology, microbiology, biogeochemistry, physiology, and ecology of microbial life in the cryosphere and atmosphere. Short descriptions of active research areas appear below:
(i) Microbial survival and metabolism under frozen conditions. Recent studies of microbial longevity in ancient frozen environments (i.e., glacier ice and permafrost) indicate that bacteria remain viable for hundreds of thousands to millions of years while frozen. In the absence of metabolic activity, macromolecular damage must inevitably accumulate through amino acid racemization, DNA depurination, and exposure to natural ionizing radiation (e.g., 40K). Our experiments have shown that microbial cells are partitioned into the solute-rich liquid veins at ice crystals boundaries and are capable of some level of metabolism at temperatures as low as -80oC. Using this established laboratory model, our current investigations are directed towards elucidating the biochemical, physiological, and molecular adaptations that are central to metabolic function under these extreme conditions.
(ii) Geomicrobiology of Antarctic basal ice. The entrapped gas concentrations in basal ice sections recovered from the Taylor Glacier (McMurdo Dry Valleys, Antarctica) have extremely high CO2 concentrations (up to 30% in some horizons) and are depleted in O2 relative to atmospheric values. These data, together with good evidence for active heterotrophic microorganisms, imply that microbial respiration is occurring within the ice at the in situ temperature of -17oC. Experiments are currently underway to connect nutrient availability, geochemical composition, and gas composition with microbial cell density, diversity and metabolic status in the basal ice sequence. The implication of this research is that microbial metabolism within the ice may alter the entrapped gas composition and that the World’s glaciers and ice sheets may represent active biomes.
(iii) Limnology of subglacial Antarctic lakes. Our research group is currently involved in an integrated study of the subglacial environments beneath the Whillans Ice Stream in West Antarctic. This research is examining distinct, but hydrologically connected, subglacial environments using a combination of biogeochemical and genomic measurements to answer key questions directly relevant to metabolic and phylogenetic biodiversity, as well as the biogeochemical transformations which occur beneath the ice sheet. We are testing specific hypotheses relevant to the geomicrobiology of discrete habitats located along a subglacial hydraulic continuum: subglacial lake water and lake sediment→ sediments associated with subglacial lake drainages→grounding zone sediments→grounding zone water. We hypothesize that these habitats will have trophically simple food webs compared to most aquatic and sedimentary ecosystems. If this is true, the layers of biological complexity are relatively few and thus the power with which the functioning of biological processes can be understood is very high.
(iv) Biological ice nucleation and bioprecipitation. Some of the microbes in the atmosphere likely play an active role in their dissemination via precipitation due to their capacity to catalyze ice formation [i.e., biological ice nuclei (IN)]. Furthermore, biologically-catalyzed ice formation in the atmosphere may be important in the processes leading to precipitation. The ecological/biological sources of biological IN have not been systematically investigated or identified, their meteorological role remains ambiguous, and information on their overall distribution in the atmosphere is very limited. Our working hypothesis is that atmospheric precipitation returns certain airborne microbial species to surface habitats and biological IN have the capacity to affect climate in ways that have not been previously considered. Future investigations will provide essential data for defining the roles of microbes in atmospheric processes and how atmospheric processes (e.g., transport and immersion in droplets/crystals) affect the dispersion of aerosolized microbes.
(v) Determining the high altitude limits of the biosphere. We have designed, fabricated, and are currently field testing the next-generation in instruments for biological sampling of the upper troposphere and stratosphere. The approach we have developed will allow measurements that 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. Establishing the high altitude boundaries for life on Earth is of inherent merit; however, it also provides important information that can be applied to assess the habitability of other planetary environments. The techniques developed to sample the stratosphere might be directly applicable to astrobiological investigations and provide the experimental technology and rationale to sample and conduct measurements in the atmospheres of other planets (e.g., Jupiter, Mars, and Venus) and moons (e.g., Titan) in the solar system.
Christner, B.C. 2010. Bioprospecting for microbial products that affect ice crystal growth and formation. Applied Microbiology and Biotechnology, 85:481-489.
Phillips, V.T.J., C. Andronache, B.C. Christner, C.E. Morris, D.C. Sands, A. Bansemer, A. Lauer, C. McNaughton, and C. Seman. 2009. Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically. Biogeosciences, 6:987-1014.
Amato, P., S.M. Doyle, and B.C. Christner. 2009. Macromolecular synthesis by yeasts under frozen conditions. Environmental Microbiology, 11:589-596.
Amato, P., and B.C. Christner. 2009. Energy metabolism response to low temperature and frozen conditions in Psychrobacter cryohalolentis. Applied and Environmental Microbiology, 75: 711-718.
Christner, B.C., R. Cai, C.E. Morris, K.S. McCarter, C.M. Foreman, M.L. Skidmore, S.N. Montross, and D.C. Sands. 2008. Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow. Proceedings of the National Academy of Sciences USA, 105:18854-18859.
Priscu, J.C., B.C. Christner, J.E. Dore, B.N. Popp, M.B. Westley, and K.L. Casciotti. 2008. Supersaturated N2O in a perennially ice-covered lake: molecular and stable isotopic evidence for a biogeochemical relict. Limnology and Oceanography, 53:2439-2450.
Raymond, J.A., B.C. Christner, and S.C. Schuster. 2008. An ice-adapted bacterium from the Vostok Ice Core. Extremophiles, 12:713-717.
Christner, B.C., C.E. Morris, C.M. Foreman, R. Cai, and D.C. Sands. 2008. Ubiquity of biological ice nucleators in snowfall. Science, 319:1214.
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.