UC San Diego

Antarctica hosts an expanse of ecological niches that approach the biophysical limits of life. Many landscape features, including sea ice, transient meltwater streams and ponds are defined by their impermanence. Instability within these systems is further complicated by the impingement of global climate change. Microbial communities flourishing within short-lived polar oases display a consortium of cold-thriving bacteria, eukaryotic algae, protists and micro-invertebrates. This thesis explores the diversity of these microbiota, the environmental drivers shaping biogeographical distribution patterns and the molecular underpinnings of responses to rapid physical and chemical fluctuations. In Chapter 1, we utilize meta-omics tools to characterize the diversity and functionality of microbial mats in the Antarctic Dry Valleys trainset streams over spatiotemporal gradients. Findings shed light on the rapid turnovers in community structure following high flow and desiccation periods. Results provide a new view of active intra-stream diversity, biotic interactions and alterations in ecosystem function over a natural hydrological regime. Additionally, we document novel antifreeze activity in several Dry Valleys endemic taxa. In Chapter 2, we conduct a broad survey of molecular diversity on aquatic habitats of Victoria land, Antarctica. This research identifies salinity as a major driver of microbial diversity and identifies a marine eukaryotic community assemblage at the base of the Taylor Glacier. In Chapter 3 we focus on understanding the adaptations and acclimation responses of polar and temperate diatoms to cold stress while exploring the functionality of ice-binding protein (IBP) coding sequences. Heterologous expression and targeted delivery of sea ice diatom antifreeze proteins into a temperate diatom resulted in a significant reduction of mortality upon exposure to freeze/thaw cycling. Data in this chapter emphasizes the efficacy and predicts the essentiality of this adaptation to cold-thriving organisms.