Abstract: The mechanisms enabling bacteria to be metabolically active at very low temperatures are of considerable importance to polar microbial ecology, astrobiology, climate and cryopreservation. This research program has two main objectives. The first is to investigate metabolic activities and gene expression of polar marine psychrophilic bacteria when confronted with freezing conditions at temperatures above the eutectic of seawater (<54C) to unveil cold adaptation mechanisms with relevance to wintertime sea-ice ecology. The second objective is to discern if psychrophilic processes of leucine incorporation into proteins, shown to occur to -196C, amount to metabolic activity providing for the survival of cells or are merely biochemical reactions still possible in flash-frozen samples without any effect on survival. We will examine extracellular and intracellular processes of psychrophilic activity above and below the eutectic by (i) determining the temperature range of metabolic activities such as DNA synthesis, carbon utilization, respiration and ATP generation using radioactive tracer technology, including a control at liquid helium temperature (-268.9C), (ii) analyzing gene expression in ice using whole genome and microarray analyses and iii) examining the role of exopolymeric substances (EPS) and ice micro-physics for the observed activity using an in-situ microscopy technique. Results of the proposed research can be expected to aid in the determination of cellular and genetic strategies that allow cells to maintain activity at extremely low temperatures within an icy matrix and/or to resume activity again when more growth-permissive conditions are encountered. The research is an interdisciplinary collaboration involving three different institutions with participants in Oceanography, Genomics, and Geophysical Sciences. The proposed activity will support the beginning professional career of a female researcher and will serve as the basis for several undergraduate student laboratory projects.