The Fate of Microbial Life Encased in Sea Ice: Tracking Organisms and Survival Strategies Through the Arctic Winter

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Abstract of Deming ProposalEvery fall, open coastal waters of the high Arctic begin to close again as atmospheric temperature drops and sea ice forms. Organisms trapped in fluid inclusions of the ice are then held captive to increasingly severe temperature and salt concentration (typically to .20degrees C and ~20% salt) as winter progresses. The few microbial studies of winter sea ice have shown that cold-adapted (psychrophilic) heterotrophic bacteria are readily cultured from it, that metabolically active cells are associated with particulate matter in the brines, and that exopolymeric substances (EPS) may serve as cryoprotectants and a stable matrix for embedded bacteria. The fate of specific microorganisms, populations or communities during the long dark winter of the high Arctic, however, is unknown; their strategies for acquiring adequate nutrition under extreme conditions, the subject only of speculation. This project proposes to track microbial succession, at regular intervals and in vertical profile within the ice sheet, through the winter season at an established, interdisciplinary study site. Fluorescent probes will be used in quantitative, in situ hybridization analyses of ice sections, melted in isothermal-isohaline solutions. Diversity in selected samples will be further evaluated by 16S rRNA-based environmental cloning. The domain Archaea and division Cytophaga-Flavobacteria-Bacteriodes will be probed as endmember populations (expected to be low and high, respectively) and members of the psychrophilic genus, Colwellia, as representatives of culturable inhabitants. The latter are also selected due to completion of the whole-genome sequence of C. psychrerythraea strain 34H, the first psychrophilic organism to be sequenced. Available knowledge leads to the hypothesis that extracellular proteolytic enzyme activity in brine inclusions is stabilized by EPS, enabling a supply of nitrogen-rich organic compounds to heterotrophic bacteria as fuel for the winter. This concept and related ideas will be tested via in situ incubations in the ice sheet, using strain 34H and preparations of its extracellular proteases and exopolymers as amendments to sea-ice brines. The research platform will be the Canadian icebreaker, John Franklin, newly renovated for science operations in winter. The Franklin will be frozen into Franklin Bay (at the western entrance of the Northwest Passage, Canadian Archipelago) during winter 2003.2004 as part of a remarkable yearlong expedition in the region for the international Canadian Arctic Shelf Exchange Study (CASES). Results from this project will be interpreted within a strong interdisciplinary framework, given the CASES platform. Better understanding of microbial succession during winter and links to organic compounds in the ice will clarify spring conditions for carbon flux, from ice to ocean below, which can be significant regionally and globally. Environmental data on Colwellia will set the stage for sophisticated genome-based research in future. Results of in situ tests of winter survival hypotheses will provide basic knowledge applicable to more practical issues of societal interest concerning use of organisms, enzymes and other sensitive organic compounds under freezing conditions in the biomedical, aquaculture and food industries. The CASES overwintering expedition provides a unique educational and training opportunity for all involved. Participants from many countries, local Inuit villages and K-12 classrooms will be aboard the Franklin for joint field, laboratory, interdisciplinary and cross-cultural research and training. Results will be published in the peer-reviewed literature, incorporated into teaching efforts, and disseminated in venues designed to reach much broader audiences, including news and information releases from sea and video documentation of field and shipboard experiences for public viewing.