HR: 13:45h
AN: B23C-01 INVITED     [Abstracts]
TI: New Directions in the Study of Bacteria Inhabiting Very Cold Sea-Ice Formations
AU: * Deming, J W
EM: jdeming@u.washington.edu
AF: Jody W. Deming, School of Oceanography Box 357940 University of Washington, Seattle, WA 98195 United States
AB: The development of new techniques for evaluating physical, chemical and microbial aspects of unmelted ice formations has led to a series of revelations about very cold saline ice (Arctic winter sea ice) as a habitat for life. Some of the remarkable features observed microscopically in unmelted ice at temperatures down to at least minus 15 degrees C include the physical connectivity of liquid brine inclusions on a micrometer scale, the extensive presence of complex exopolymers within the fluid inclusions, and the apparent attachment of dividing bacteria to the ice wall of a brine pore. When coupled with studies that involve melting ice but into salt solutions to minimize thermal and osmotic shocks to bacteria located within the brine inclusions, the hypothesis that bacterial activity continues even at the coldest temperature yet tested (minus 20 degrees C) has been supported. I recently worked to extend the study of very cold unmelted and brine-melted sea ice to include an assessment of extracellular enzyme activity (EEA). In other porous but less extreme environments, the detection of EEA (dominated by proteolytic activity) has reflected an important foraging strategy in use by heterotrophic bacteria dependent on acquiring small-sized, nitrogen-rich organic compounds for their livelihood. Taking advantage of facilities aboard the Canadian icebreaker Amundsen, newly renovated for science and frozen into Franklin Bay (Canadian Arctic) during winter 2004, I explored means to test for EEA (particularly leucine amino-peptidase activity), using fluorescently labeled substrate analogs, under in situ ice-brine conditions and over a range of temperatures and salt concentrations. Although methods remain to be fully optimized, preliminary results indicated detectable EEA down to minus 12 degrees C, with thermal optima much lower than previously detected in warmer (summer) sea ice and examples of possible activity at minus 18 degrees C, the lowest temperature tested. Graphical analyses of EEA in temperature-salt space suggested that high salt concentrations limit enzyme performance at the coldest temperatures, while other experiments pointed to the presence of particulate matter or exopolymers in the ice as possibly compensating for negative salt effects. The detection of enzyme activity under the extreme conditions of winter sea ice bears upon the nature of organic compounds found concentrated within the ice matrix (and available for release during the melting season), bacterial success in extremely cold ice formations, and the discussion of possible life processes in extraterrestrial saline ices.
DE: 4840 Microbiology
DE: 5462 Polar regions
DE: 6020 Ice
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting