Anoxic marine systems are key regions of nitrogen loss mediated by anaerobic microbial communities and contribute ~50% of global loss of bioavailable nitrogen to the atmosphere. This dissertation used culture-dependent and culture-independent methods to explore nitrogen loss metabolisms in novel microbial species in two anoxic marine systems: the Eastern Tropical North Pacific oxygen deficient zone and the Orca Basin deep hypersaline anoxic basin in the Gulf of Mexico. Using metagenomics and metatranscriptomics, I found that the most abundantly transcribed nitric oxide dismutase genes in the Eastern Tropical North Pacific oxygen deficient zone belong to a novel order (UBA11136) of Alphaproteobacteria that couple oxidation of one-carbon compounds with aerobic respiration, possibly using oxygen from nitric oxide dismutation. I then isolated and characterized a novel bacterial species, Marinobacter pacificus from the Eastern Tropical North Pacific oxygen deficient zone and characterized the bacterium with epifluorescent microscopy and proteomics. When grown on methane and nitrate, Marinobacter pacificus autofluoresces and highly expresses genes for methanol/ethanol oxidation and denitrification, a metabolism not previously reported in Marinobacter species. I then enriched bacterial cultures with methane, manganese, and nitrate as substrates from ~2200 meters at Orca Basin brine-seawater interface. Marinobacter species were dominant, and consumed nitrate while producing manganese oxides. I found previously described chemolithoautotrophic manganese oxidizing bacteria were present and transcriptionally active for manganese oxidation at ~2200 meters as well. Understanding the full breadth of diverse electron acceptors that drive denitrification in anoxic marine systems, where organic carbon is depleted, is essential to understand nitrogen loss in globally important systems.

March 11, 2025, 10 am, Ford ES&T 3235 (Ocean Room) (Hybrid Option via Zoom: Click here)

Thesis Advisor:

Dr. Jennifer Glass, Ph.D.

School of Earth and Atmospheric Sciences

Georgia Institute of Technology

Committee Members:

Dr. Joel Kostka, PhD

School of Biological Sciences

Georgia Institute of Technology

Dr. Ameet Pinto, PhD

School of Civil and Environmental Engineering

Georgia Institute of Technology

Dr. Frank Stewart, PhD

Department of Microbiology

& Cell Biology

Montana State University 

Dr. Laura Bristow, PhD

Department of Marine Sciences

University of Gothenburg