Title

An Investigation Correlating Bioluminescence and Metal Ruduction Utilizing Shewanella woodyi

Date of Award

1-1-2019

Degree Name

M.S. in Chemistry

Department

Department of Chemistry

Advisor/Chair

Advisor: Justin Biffinger

Abstract

The internal transfer of electrons through proteins from low to high electrochemical potentials is a fundamental aspect of life. Some microbes possess the unique ability to transfer electrons generated inside of the cell to external insoluble electron acceptors such as electrodes, redox proteins, and other cells in a process known as extracellular electron transfer (EET). Currently, this microbial process is applied in the creation of microbial electrochemical systems (MESs). These devices are part of a variety of renewable energy and wastewater treatment research and applications. Shewanella woodyi is a cold tolerant, marine microbe that is an understudied candidate for metal reduction processes. S. woodyi is closely related to other well-characterized strains in the Shewanella genus that are models for studying fundamental electron transfer mechanisms. Additionally, S. woodyi is bioluminescent and previous research indicates that a relationship between bioluminescent intensity and EET exists using fixed potentials. The bioluminescence enzyme luciferase cluster in this bacterium relies on reduced flavin cofactors to generate light. Therefore changes in flavin redox state and concentration can have an impact on bioluminescence from the bacterium and its extracellular metal reduction rates. The general growth of S. woodyi under defined growth conditions was monitored to determine the ideal conditions to study the connection between bioluminescence and EET. Additionally, the relationship between EET and bioluminescence was confirmed utilizing the soluble electron acceptors cobalt (II) and nitrate as the terminal electron acceptor to anaerobic and aerobic growth. Through high throughput luminescence assays and open circuit potential experiments under microaerophilic and anaerobic atmospheres, we determined that increasing concentrations of the electron acceptors resulted in decreased bioluminescence output from the cells. Cell viability staining results suggest that the increased concentrations of acceptors were not decreasing the viable cell density and consequently the overall luminescence from the cells. Thus, this data indicates there is a valid relationship between EET and bioluminescence in S. woodyi.

Keywords

Chemistry, Microbiology, Shewanella woodyi, extracellular electron transfer, EET, microbial metal reduction, microbial electrochemical systems, bioluminescence

Rights Statement

Copyright 2019, author

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