The microbial ecology of deep-sea hydrothermal vents
Creators: name: Grosche, Ashley Elaine
Publisher: name: No Publisher Supplied
Year: 2018

description: Deep-sea hydrothermal vents are a global phenomenon driven by reservoirs of geothermal energy that chemically transform seawater through the enrichment of minerals from the interacting basement crust. The chemical enrichment resulting from seawater-rock interactions at high temperature fuels microbial metabolism and enables life to flourish at a depth of the ocean typically characterized by low biomass. These systems are among the most biologically productive in the world, and rely on chemosynthesis, rather than photosynthesis, for primary production.   The aims of this dissertation are to determine the microbial biogeography of biofilm communities at a basalt-hosted deep-sea hydrothermal vent system, constrain the functional diversity as it relates to habitat composition, and compare the phenotypic profiles of pure-culture representatives with genotypes using comparative genomics in order to verify gene function, and explore novel adaptations that may play a role in the ecological success of these taxa at vent ecosystems.  To determine the microbial biogeography at deep-sea vents, biofilms were analyzed from across three distinct “bioregimes” or habitat zones, each characterized by colonization patterns of macrofauna and local fluid chemistry, which was concurrently measured during sampling. This study revealed that age, colonization substrate, and bioregime are major drivers of variation between communities, and that populations abundant during the early stages of colonization and late stages of biofilm maturity shared many of the same species, but could be distinguished at the OTU-level, revealing differential populations of pioneer and secondary colonizers. Metatranscriptomic analysis of a biofilm from the Riftia bioregime and hydrothermal fluids was also performed to discern functional adaptations in sessile communities. Gene transcripts related to central metabolism  (e.g., carbon fixation, sulfur and nitrogen metabolism) and environmental adaptations (e.g., motility and chemotaxis, oxidative detoxification) were identified.  Subsequent studies investigated the metabolism and physiology of a bacterial isolate from the East Pacific Rise hydrothermal vent system. Cetia pacifica strain TB-6T represents a novel genus with the Nautiliales, an order within the Epsilonproteobacteria whose validly described genera are found exclusively in association with deep-sea vents. C. pacifica is an obligate anaerobe, hydrogen-oxidizing, sulfur- and nitrate-reducing thermophile that utilizes the reductive citric acid cycle (rTCA) to fix carbon dioxide. Since phenotypic redundancy is exhibited by Cetia and other genera within the Nautiliaceae family, further investigation focused on a comparative genomic analysis of the Nautiliaceae to discern if genotypic redundancy was present as well. Central metabolism (C, H, N, S, P) was conserved within the family.  However, a set of accessory genes was also identified, including an alginate biosynthesis pathway previously found in only two other bacterial genera (Pseudomonas and Azotobacter). Overall, the work outlined in this dissertation contributes to our understanding of microbial abundance, distribution, and function at deep-sea hydrothermal vents.