UC San Diego

Marine prokaryotes are ubiquitous within the ocean and are important drivers of various carbon and nutrient cycles globally. Having a broader understanding of the roles marine microbes play in the ocean requires examining the physical and chemical parameters that modulate their survival, reproduction, and activity at levels extending from the molecular to the global. In this dissertation, I investigate the role that cosmopolitan Gammaproteobacteria play within the oceans across a variety of scales. Using isolated cultures, I show that high hydrostatic pressure and low temperature have compounding negative effects on the motility of three mesophilic marine bacteria but that the nature of these impacts varies significantly among the species. During the course of these studies, I also developed a high-pressure capillary-based chemotaxis assay and demonstrated, for the first time, that microbial chemotaxis is one of the most pressure-sensitive cellular processes yet described. Through participation in an International Ocean Discovery Program expedition, I also enriched and isolated microbes from serpentine mud volcanoes, where they were exposed to polyextreme conditions, including high pressure and high pH. Results from the preparation of novel high-pressure, high pH, low temperature, and anaerobic microcosms are described, including the temporary enrichment of taxa with no or few cultured representatives. The comparative genomics of select mud volcano alkaliphiles within the Halomonas and Marinobacter genera have highlighted some of their polyextreme adaptations. The global metabolic versatility and niche adaptations of clades within these genera have also been examined using an extensive dataset of publicly available genome sequences. This dissertation leverages the culturability and cosmopolitan nature of marine Gammaproteobacteria to uncover new features of their environmental adaptations at a variety of scales.