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Project Progress

Laboratory observations of bacterial motility and field observations of bacterial attachment led to the testable hypothesis that a temperature threshold exists in ice formations (-10°C in sea ice), below which bacteria cease moving as a means to locate optimal resources and conditions and instead become attached to a surface (first-stage biofilm formation), which allows for continued activity down to -20°C (lowest temperature tested yet). The relevant observations and hypothesis have been published (Junge et al., 2003) or submitted for publication (Junge et al., Submitted, 2003) and further experimental tests are underway. We have also introduced a new aspect to first-stage biofilm formation in the cold: the role of bacterial viruses in altering bacterial behavior and possibly triggering attachment. Building on our finding of considerable morphological diversity of bacteriophage in subzero Arctic seawater (Wells and Deming, Submitted, 2003) and on field work last fall (CASES 2002 expedition), novel phage-host systems were established in the laboratory, using the obligately psychrophilic (cold-loving) bacterium, Colwellia psychrerythraea strain 34H (whole genome sequence available), as the host. Initial experiments have revealed a potential link between phage infection of a bacterium and its production of exopolymers that promote attachment (Wells and Deming, unpublished). Our overall habitat focus remains on sea ice, after having demonstrated microscopically and non-destructively (Junge et al., Submitted, 2003) that freshwater (lake) ice formations are more space-limited (contain more constricted volumes of inhabitable liquid) than ice formed from seawater. Interactions with co-I Steve Warren on polar snow as another possible, but unlikely, medium for microbial activity has further convinced us to stay with sea ice. This continued focus also recognizes the special role of salts in constraining the inhabitable space within an ice matrix (Eicken et al., 2002; Eicken, 2003; Deming and Eicken, In Preparation, 2003) in triggering specific microbial responses (largely hypothetical at this stage; Deming, 2002, 2003), and in conceivably enabling the presence of microbial biosignatures on Europa (Eicken et al., 2003). Although tangential to our low temperature research but relevant to first-stage biofilm formation under extreme conditions in general, we also completed this year our work on a new sampler for conducting in situ experiments on the seafloor using very hot fluids from active hydrothermal vents (Phillips et al., In Press, 2003).