Microbial Challenges and Solutions to Inhabiting the Dynamic Architecture of Saline Ice Formations
Ewert Sarmiento, Marcela
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Sea ice contains a microscopic network of brine inclusions effectively colonized by organisms from the three major clades of life. The architecture of this brine channel network is dynamic, with surface area, brine volume fraction, and brine salinity changing with temperature. This dynamic architecture may have also played a role in the origin and early evolution of life (Chapter 1). Sea-ice microorganisms experience multiple stressors, including low temperature, high salinity and fluctuations in those parameters. This dissertation discusses two bacterial adaptations to these challenges: the production of extracellular polysaccharide substances (EPS) and the accumulation of compatible solutes. Two Arctic bacteria were used as model organisms; the psychrophilic <italic>Colwellia psychrerythraea</italic> strain 34H <italic>Cp</italic>34H), which grows at a comparatively narrow range of salinities, and the psychrotolerant <italic>Psychrobacter sp.</italic> strain 7E (<italic>P</italic>7E), which grows at a broad range of salinities. Chapter 2 presents experimental results evaluating the establishment of the sea-ice bacterial community by means of selective enrichment of EPS. Chapter 3 presents field measurements indicating that biological components of the sea-ice brines, including bacterial cells and EPS from mixed sources (algal and bacterial), are expelled onto the ice surface and wicked upwards into snow, experiencing different degrees of cell loss depending on environmental conditions. Analysis of seasonal (Winter and Spring) <italic>in situ</italic> temperature and brine salinity data indicated that fluctuation regimes were significantly more energetic on the snow surface than in the ice column (Chapter 4), with implications for the microbial sea-ice population. Laboratory experiments exposing model organisms to freezing under constant and fluctuating regimes showed higher susceptibility to fluctuations by the stenohaline <italic>Cp</italic>34H than for the euryhaline <italic>P</italic>7E, with P7E undergoing fragmentation during the course of the freezing regime. The presence of compatible solutes significantly reduced cell loss in <italic>Cp</italic>34H. A synthesis of the microbial solutions to the challenges imposed by the dynamic structure of sea ice is discussed in Chapter 5, and testable hypotheses for future research were identified. Supporting information and the implementation of a science education and outreach activity based on this work is presented in the Appendices.
- Oceanography