Date of Award:

8-2018

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Chemistry and Biochemistry

Department name when degree awarded

Biochemistry

Committee Chair(s)

Lance C. Seefeldt (Committee Chair)

Committee

Lance C. Seefeldt

Committee

Scott A. Ensign

Committee

Bruce Bugbee

Committee

Sean J. Johnson

Committee

Nicholas E. Dickenson

Abstract

Nitrogen is a critical nutrient for growth and reproduction in living organisms. Although the Earth's atmosphere is composed of ~80% nitrogen gas (N2), it is inaccessible to most living organisms in that form. Biological nitrogen fixation, however, can be performed by microbes that harbor the enzyme nitrogenase. This enzyme converts N2 into bioavailable ammonia (NH3) and accounts for at least half of the "fixed" nitrogen on the planet. The other major contributor to ammonia production is the industrial Haber-Bosch process. While the Haber-Bosch process has made significant advances in sustaining the global food supply through the generation of fertilizer, it requires high temperature and pressure and fossil fuels. This makes nitrogenase an ideal system for study, as it is capable of performing this challenging chemistry under ambient conditions and without fossil fuels.

Nitrogenase requires energy and electrons to convert N2 into NH3. The work presented here examined how the enzyme receives electrons to perform the reaction. It was discovered that some microbes employ a novel mechanism that adjusts the energy state of the electrons so that nitrogenase can accept them. Further, the slowest step that takes place in nitrogenase once the electrons are taken up was identified. Finally, by capitalizing on fundamental knowledge, a biohybrid system was designed to grow nitrogen-fixing bacteria in association with electrodes for light-driven production of fixed nitrogen that has potential to be used as a fertilizer for plant growth.

Gaining an in-depth understanding of nitrogenase provides insight into one of the most challenging biological reactions, and the newfound knowledge may be a catalyst in developing more efficient systems for sustainable ammonia production.

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