LRES Dissertation Defense
- Friday, May 29, 2015 from 10:00am to 11:00am
- Animal Biosciences Building - view map
Ryan Jennings, PhD Candidate in Ecology and Environmental Sciences through the Land Resources and Environmental Sciences department, will present his dissertation defense titled "Inorganic carbon fixation and trophic interactions in high-temperature geothermal springs of Yellowstone National Park, WY, USA" at 10:00 a.m. in ABB 134.
Numerous chemotrophic microorganisms inhabit high-temperature (> 65 °C) systems of Yellowstone National Park (WY, USA). Prior geochemical and metagenome characterization has identified the primary electron donors and acceptors and phylotypes distributed across a range in pH and geochemical conditions. Although several chemolithoautotrophs are expected to play a direct role in the fixation of inorganic C in these communities, little work has directly identified the importance of this process in situ. Consequently, the primary goal of this thesis was to evaluate the role of CO2 fixation across numerous types of geothermal habitats and to explore autotroph-heterotroph interactions that may control community composition. Genes encoding enzymes for inorganic C fixation pathways were identified in assembled genome sequence corresponding to the predominant autotrophs (Crenarchaeota and Aquificales) observed in Fe(III)-oxide mats, sulfur sediments, and filamentous streamer communities. Carbon isotope (13C) mixing models were used to interpret the 13C compositional values of microbial samples as a function of 13C-dissolved inorganic C (DIC) and 13C-organic C (DOC and/or landscape sources). The relative abundance of autotrophs versus heterotrophs identified in complementary metagenome analysis and respective CO2-fixation fractionation factors were utilized in site-specific mixing models to calculate minimum contributions of DIC-derived microbial C across 15 different microbial communities. Genome sequence was also used to develop stoichiometric reaction networks for a primary autotroph (Metallosphaera yellowstonensis) and heterotroph (‘Geoarchaeota’) important in acidic Fe(III)-oxide mats. Possible modes of biomass production were evaluated for different C sources and/or electron donors as a function of oxygen cost. The total oxygen flux was also used to predict the rate of Fe(II)-oxidation, and these values were compared to Fe(III)-oxide deposition rates and oxygen fluxes measured in situ. Stoichiometric modeling and Elementary Flux Mode Analysis established an optimum autotroph to heterotroph ratio (2.4:1) for DIC-derived biomass dependent on Fe(II) as the electron donor. Comparison of predicted Fe(II)-oxidation rates with observed Fe(III)-oxide deposition rates and oxygen flux measurements using microelectrodes suggest the importance of other oxygen consuming processes. Results from this thesis demonstrated the importance of inorganic C fixation in numerous geochemically distinct high-temperature microbial habitats, and the potential for DIC-derived biomass to support other hyperthermophilic heterotrophic organisms.
- Department of Land Resources and Environmental Sciences