Sulfur and oxygen isotope insight into microbial sulfur\ud metabolism
Dissimilatory microbial sulfate reduction (MSR) is a process where microbes utilize sulfate as an electron acceptor to oxidize organic matter in anoxic environments. In modern marine sediments, MSR is responsible for over half of the anoxic oxidation of organic matter. In addition, the anaerobic oxidation of methane (AOM) is coupled largely to MSR in marine sediments, in a process called sulfate-driven AOM, preventing the Earth’s oceans from becoming a major source of this potent greenhouse gas to the surface. \ud The aim of this thesis was to elucidate the pathways of MSR coupled to organic matter oxidation and AOM by using a largely geochemical approach; specifically the chemical and isotope (C, S, O) variation in pure-culture sulfate reducing bacteria and sedimentary pore fluid profiles. I use this data to better understand how sulfate is involved in different diagenetic processes. The most powerful tool that used was the combined measurement and modeling of sulfur and oxygen isotopes in sulfate (δ18OSO4 and δ34SSO4, respectively), which enabled me to model how sulfate is recycled within pure cultures as well as the natural environment.