Date of Award

5-2026

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Silvia Rossbach, Ph.D.

Second Advisor

Kathryn Docherty, Ph.D.

Third Advisor

Benjamin Koestler, Ph.D.

Fourth Advisor

Johnson Haas, Ph.D.

Access Setting

Masters Thesis-Open Access

Abstract

Microbial life is not only ubiquitous but also plays a critical role in the geochemical makeup of our planet. While researchers have long studied easily culturable aerobic microbes, the influence of anaerobic life on soils and mineral cycling is less understood. Notably, knowledge about interactions between anaerobic microbes and inorganic elements such as iron has progressed with the discovery that magnetite influences how anaerobic archaea carry out methanogenesis. To better understand anaerobic bacterial metabolisms and how they interact with minerals and subsurface hydrocarbons, we extracted 16S rRNA genes from two adjacent subsurface petroleum plumes, sequenced the DNA, and analyzed it using programs such as QIIME2 and PICRUSt. We retrieved soil cores from the same sites for laboratory microcosm experiments, incubated them anaerobically, and monitored them for changes in methane and iron concentrations. This thesis found that the two petroleum plumes, located 100 m apart, hosted distinct microbial communities, with the dominant methanogenic genera differing and, in the newly analyzed pool, representing an uncultured member of Methanoculleus. The microcosm experiment showed that the methanogens in the soil respond to added magnetite supplements, and that iron oxides initially suppress methane production before later accelerating it, likely due to microbial conversion of iron into magnetite. This research contributes to our knowledge of soil microbiology, particularly how the composition of aged, subsurface petroleum plumes and mineral content of soils affect anaerobic microbial metabolisms and communities.

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