Research Overview

The Christner Research Group uses a combination of laboratory and field approaches to study microbes and their processes in subglacial/subsurface aquatic ecosystems, glaciers and ice sheets, and the atmosphere.

Microbial aerosols, clouds, and precipitation: Ice formation in clouds is important to the meteorological processes that lead to precipitation, and aerosol particles can assist with this by nucleating ice from water vapor or freezing water droplets directly. Our research has shown that certain microbial aerosols possess proteins or other biomolecules that allow them to have an active role in their dissemination via precipitation. The meteorological interactions of biological ice nucleating particles provide insight into the potential mechanisms that allow terrestrial biomes to exert control on synoptic conditions that promote or suppress rainfall. Improved understanding of biological-meteorological feedbacks opens the possibility for altering land use in ways that increase precipitation, contribute to food security, and optimize water use.

Microbial transport and survival in the stratosphere: From altitudes in the upper troposphere and stratosphere, we have isolated a range of bacteria with extreme resistance to desiccation and shortwave ultraviolet radiation. Ongoing characterization of these bacteria is contributing to our understanding of the tenacity of life to water deficit, helping to constrain the boundaries for life on Earth, and is providing a wealth of information on the genetic basis for extremophile phenotypes. Since conditions at an altitude of ~30 km above the Earth are similar to the pressure, temperature, and radiation levels present on the surface of Mars, the information gained would be valuable to discussion regarding astrobiological investigations and microbial survival in the thin atmospheres of other planets and moons in the solar system.

Microbial persistance in ancient ice: Studies of ancient ice cores have demonstrated that microbes survive for hundreds of thousands of years while frozen. Experimental data indicate a variety of microorganisms can sustain a sufficient metabolic function for cellular repair and maintenance under frozen conditions, and we now understand that a solute-rich liquid phase at ice crystal boundaries provides habitat suitable for microorganisms. Provided that sufficient energy and nutrient sources are available, the capacity to remain metabolically functional in frozen matrices suggests that it may be possible for microbes to maintain genome integrity and survive in icy terrestrial or extraterrestrial environments for timeframes in excess of a million years.

Subglacial Antarctic lakes: Approximately 400 lakes have been identified under the Antarctic ice sheet and we have been involved in the only two projects that have successfully drilled through the ice sheet and sampled subglacial Antarctic lakes. The West Antarctic subglacial lakes we are studying (Whillans Subglacial Lake and Mercer Subglacial Lake) contain exclusively microbial ecosystems and operate under conditions of permanent darkness, cold, and low energy. In addition to reservoirs of organic carbon stored in the subglacial sediments, glacier flow produces finely crushed rock that generates redox couples that promote biomass production via chemolithoautotrophic metabolisms. We are very interested in learning more about ecological, evolutionary, and biogeochemical processes in subglacial microbiomes.

Geomicrobiology of ice sheet retreat: As large ice sheets retreat across the land, they change landscapes, ecosystems, and waters in profound ways. While we know that “deglaciated” streams in Greenland have distinct chemical compositions from those sourced by glacial melt, we are currently working to understand better the geomicrobiological processes that control the differences in water chemistry and the release of greenhouse gases and nutrients from these streams to the atmosphere and ocean, respectively. Changes in the Arctic will have distinct global impacts that depend on individual responses of each environment within the assemblages, which emphasizes the need to develop a holistic understanding of this system and the ability to communicate the understanding to policymakers.

Karst aquifers: The karstic Upper Floridian Aquifer underlies northern regions of the Floridian peninsula and parts of southern Georgia and Alabama and is Florida’s largest freshwater reservoir. The linkage between hydrology, microbes, and water composition has remained elusive because few interdisciplinary studies have simultaneously measured biogeochemical reactants/products, metabolic rates, and shifts (or stability) in microbial community compositions and functions over time. We are interested in how water exchange between the surface and subsurface affects the composition/function of microbial communities and the export of biologically relevant nutrients and greenhouse gases from the aquifer.

Current Research Projects:

Subglacial Antarctic Lakes Scientific Access (SALSA): Integrated Study of Carbon Cycling in Hydrologically-active Subglacial Environments

The Antarctic subglacial environment remains one of the least explored regions on Earth. This project will examine the physical and biological characteristics of Subglacial Lake Mercer, a lake that lies 1200m beneath the West Antarctic Ice Sheet. This study will address key questions relating to the stability of the ice sheet, the subglacial hydrological system, and the deep-cold subglacial biosphere. The education and outreach component aims to widely disseminate results to the scientific community and to the general public through short films, a blog, and a website. Subglacial Lake Mercer is one of the larger hydrologically active lakes in the southern basin of the Whillans Ice Plain, West Antarctica. It receives about 25 percent of its water from East Antarctica with the remainder originating from West Antarctica, is influenced by drain/fill cycles in a lake immediately upstream (Subglacial Lake Conway), and lies about 100 km upstream of the present grounding line of the Ross Ice Shelf. This site will yield information on the history of the Whillans and Mercer Ice Streams, and on grounding line migration. The integrated study will include direct sampling of basal ice, water, and sediment from the lake in concert with surface geophysical surveys over a three-year period to define the hydrological connectivity among lakes on the Whillans Ice Plain and their flow paths to the sea. The geophysical surveys will furnish information on subglacial hydrology, aid the site selection for hot-water drilling, and provide spatial context for interpreting findings. The hot-water-drilled boreholes will be used to collect basal ice samples, provide access for direct measurement of subglacial physical, chemical, and biological conditions in the water column and sediments, and to explore the subglacial water cavities using a remotely operated vehicle equipped with sensors, cameras, and sampling equipment. Data collected from this study will address the overarching hypothesis "Contemporary biodiversity and carbon cycling in hydrologically-active subglacial environments associated with the Mercer and Whillans ice streams are regulated by the mineralization and cycling of relict marine organic matter and through interactions among ice, rock, water, and sediments". The project will be undertaken by a collaborative team of scientists, with expertise in microbiology, biogeochemistry, hydrology, geophysics, glaciology, marine geology, paleoceanography, and science communication.
Funding: National Science Foundation, Office of Polar Programs

THOR (Thermal High-voltage Ocean-penetrator Research platform)

Robotic exploration and life search on ocean worlds requires the ability to access habitable ocean environments concealed beneath thick ice crusts. Additionally, an instrument suite is required to perform the complicated task of autonomous life detection. We propose to address these technological and operational requirements for ocean world access with THOR, a robust cryobot capable of rapid (10 m/hr), deep (500+ m) subglacial access that carries an onboard science payload optimized for environmental characterization and life detection. THOR will be deployed at the eastern Skaftafell subglacial lake in Vatnajokull, Iceland where it will penetrate the thick ice cover of the lake. Successful fielding of THOR will mark the first cryobot descent into a subglacial lake, thus enabling unique investigations of both the lake's geomicrobiology and of CONOPS strategies for a cryobot's entry into, and descent through, a subglacial body of water. The THOR cryobot will penetrate a 300 m thick glacier and enter the subglacial lake in the volcano's crater while carrying a suite of instruments chosen to characterize the environment of the ice and subglacial lake, with a specific focus on life-detection strategies. Comparative analysis will utilize water column and vent material samples, which will be returned to the surface and analyzed. The THOR platform will enable unprecedented access to subglacial environments, making it an ideal payload delivery system for ocean worlds technology development and research on subglacial aquatic environments.  
: National Aeronautics and Space Administration, The Planetary Science and Technology from Analog Research (PSTAR) Program

Assessing the impact of biological aerosols on rainfall: effects of land cover diversity and landscape properties

The aim of this study is to improve understanding of the conditions under which biological aerosols influence atmospheric processes that lead to rain. Aerosols influence clouds and can limit rainfall; however, their ubiquity in the atmosphere has complicated efforts to identify the specific situations in which they have decisive roles. To clarify this, we will exploit knowledge on rainfall feedback (RF), a process where rainfall has a measurable influence on subsequent rainfall. We hypothesize that RF occurs because bioaerosols that can catalyze the freezing of water in clouds are emitted from plants after rainfall, are transported into the atmosphere, and influence the formation of ice in clouds. A comprehensive analysis of the relationship between land use (LU), topography, and RF at >2000 sites in the continental US will identify sites with similar relationships and the biological aerosol sources. The outcome will be proposed methods to combat drought by modify LU to favor rainfall.  
: Thomas Jefferson Fund

High Latitude Hydrology: Water in a Changing World

The 2019 Water Institute Graduate Fellowship program offers a novel interdisciplinary graduate training environment, focused on water through the lens of the Arctic. We aim to foster interdisciplinary research and outreach among researchers, practitioners, and students in geology, hydrology, microbiology, botany, ecosystem science, coastal hydrodynamics, and communications. Students in the cohort will train in environmental civics, defined as the principles and practice of public engagement, including general audience communication skills, policy discourse, and civic leadership.
: University of Florida, Water Institute grant

Significance of Ice-loss to Landscapes in the Arctic: SILA (Inuit concept of the physical world and weather)

Sediment compositions, exposure age, plant and microbe colonization, water availability, and stream-landscape connections are hypothesized to vary systematically across periglacial watersheds and thus control weathering extent, stream geochemistry, and solute and gas fluxes. This hypothesis will be tested in watersheds stretching from the Greenland Ice Sheet to the coast over two melt seasons by an interdisciplinary group of U.S. and Greenlandic researchers who will a) measure non-glacial stream discharge, solute and gas concentrations and fluxes, microbial community structures, plant community distributions, carbon and nutrient cycling, and radiogenic isotopes in stream and bedload sediment; b) maintain automated weather observations, dust collection, and stream chemistry loggers; and c) perform stream dosing experiments. These data will reveal feedbacks between weathering extent, ecosystem characteristics, biogeochemical processes, and stream chemistry and their controls on solute and gas fluxes from periglacial watersheds. In collaboration with Greenlandic colleagues, the results will seed environmental civics plans to develop and implement environmental science curricula at levels appropriate to Greenlandic high schools through a teacher-education program and to create educational materials for tourism in Greenland, Greenlandic secondary schools, and the Arctic Technology Center.
: National Science Foundation, Office of Polar Programs

Understanding the genetics of extreme stress resistance in bacteria

The overall goal of this work is to characterize the molecular genetics and mechanisms of resistance to extreme stressors in Gram positive and negative isolates recovered from 21 to 26 km above Earth’s surface. Based on preliminary analysis, we hypothesize that different mechanisms are responsible for the polyextremophilic phenotypes observed. To investigate this hypothesis and the mechanisms of resistance, we propose to study of two stratospheric isolates to meet the following objectives.
1. Identify genes responsible for UVC radiation resistance in an isolate from the Gram positive genus Curtobacterium by comparative analysis of sensitive and resistant strains.
2. Identify the genes responsible for UVC radiation resistance in an isolate from the Gram negative genus Noviherbaspirillum by transposon mutagenesis and transcriptomics.
3. Determine if the UVC resistance mechanisms confer resistance to other stressors by genetic reconstruction.
: National Aeronautics and Space Administration, Exobiology

Biomass burning smoke as a driver of multi-scale microbial teleconnections

Microbial emissions in smoke from biomass burning are both quantitatively and qualitatively different from the bioaerosols observed from wind-driven emissions, implying that wildland fire may be a globally relevant and yet-unquantified mechanism for microbial teleconnections among ecosystems. To test how smoke drives microbial metacommunity ecology, this project will use an integrated approach that compares the composition and viability of smoke source and sink microbial assemblages in field- and laboratory-based experiments. Smoke and particulate deposition during repeated prescribed fires in grasslands will be sampled over two years to characterize the relationships among fire behavior, meteorological conditions, and survival of microbes transported in smoke. Sterilized and untreated soils from similar, unburned sites will be exposed to contrasting dosages of smoke with known microbial content to compare the relative influence of selection, dispersal, and drift on soil microbial community assembly. These data will be used to build new capacity for simulating smoke microbial dispersal across scales by parameterizing microbial emission fluxes and microbial dispersion in atmospheric, chemical transport, and coupled fire-atmosphere models. Results will lend insight into the relative importance of stochastic vs. deterministic processes in driving microbial community ecology in systems where fire disturbances are frequent, while modeling will enable predictions of the scale and impact of smoke-related microbial dispersal. This research will inform questions about microbial gene flow, microbial pathogen epidemiology, phytopathogens, and meteorological processes, and will expand fundamental understanding of fire’s ecological significance.
: National Science Foundation, Division of Environmental Biology

Past Grants:

ARCHIMEDES (A Really Cool High Impact Method for Exploring Down into Europan Subsurface)

Funding: National Aeronautics and Space Administration, COLDTech

MICROFLORA (MIcrobial Communities that Remain Obscure in the FLORidan Aquifer)

Funding: UF Biodiversity Institute 

A Transoceanic Aerobiology Biodiversity Study (TABS) to Characterize Microorganisms in Asian and African Dust Plumes Reaching North America

Funding: National Aeronautics and Space Administration, Biodiversity

EMBER: Exploring Microbial Bioaerosol Effects on Rainfall 

Funding: Orway Swisher Biological Station Jumpstart Award Program (McIntire-Stennis, National Institute of Food and Agriculture - United States Department of Agriculture)

Research on Airborne Ice Nucleating Species (RAINS)

Funding: National Science Foundation, Dimensions of Biodiversity 

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

Funding: National Science Foundation, Antarctic Integrated System Science

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

Funding: National Aeronautics and Space Administration, Astrobiology Science and Technology for Exploring Planets (ASTEP)

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

Funding: National Aeronautics and Space Administration, Astrobiology: Exobiology and Evolutionary Biology

Greenland melt water Geomicrobiology

Funding: National Science Foundation, Arctic Sciences Division

High Elevation Impact Sampling Tool (HEIST)

Funding: National Aeronautics and Space Administration, Undergraduate Student Instrument Project (USIP), Educational Flight Opportunity for University Undergraduate Students

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

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

Funding: National Science Foundation, Antarctic Organisms and Ecosystems

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?

Funding: Louisiana State University, Office of Research and Economic Development, 2007-08