LEXEN: A Collaborative Proposal on Geophysical Constraints on Sea-Ice Bacteria: Implications for Life on Ice-Covered Solar Bodies

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ABSTRACTDeming, JodyEicken, HajoThe overall goal of the project is to better understand, at relevant spatial scales, the geophysical constraints on bacterial activity at very low temperatures in the brine pores of wintertime sea ice. The role of solid surfaces as attachment sites for bacteria figures strongly in the formulation and testing of hypotheses. The three main objectives are: 1) to characterize the evolution and spatial distribution of the different phase components in sea-ice pores on scales relevant to microorganisms; 2) to determine the in-situ distribution of bacteria within the ice matrix and their association with different surfaces; and 3) to examine bacterial activity in brine solutions at temperatures from 4 to -300C as a function of concentration of dissolved organic matter and presence of different surfaces. The research approach combines field observations of Arctic sea ice (known to entrain mineral surfaces) with novel laboratory experiments designed to characterize micro-physical features of sea-ice as it evolves at decreasing temperature and to measure microbial reactions to increasingly extreme thermal and chemical conditions. The plan relies upon standard methods for assessing bacterial abundance and location (epifluorescence and scanning electron microscopy) and selected metabolic activities (substrate uptake and extracellular hydrolysis), but applied in new ways (after ice sublimation, to viscous sub-zero brines). Standard methods for physical and chemical assessments of sea ice will also be employed, but in combination with novel techniques (micro-scale collections by sublimation, NMR). Results will significantly expand the knowledge base for predicting the lower temperature threshold for microbial life on Earth and possibly elsewhere on ice-covered solar bodies. They should also enhance understanding of the seasonal functioning of polar microbial ecosystems and sea-ice itself, as it effects the global heat budget and climate, and practical applications of low-temperature bacteria and enzymes in biotechnology.