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Author ORCID Identifier

https://orcid.org/0000-0001-5612-5687

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Microbiology

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

Kristen M. DeAngelis

Second Advisor

James F. Holden

Third Advisor

Klaus Nüsslein

Fourth Advisor

Michael Henson

Abstract

There is a growing need to reduce reliance on non-renewable fuels, especially fossil fuels that contribute to the climate crisis. Plant lignocellulose is an abundant and undervalued source of energy, but its use is hindered due to the recalcitrance of the lignin-component. Current methods to remove lignin have sustainability concerns and are costly for industrial applications such as paper mill pulping. An alternative and greener approach is biopulping, which uses microbes and their enzymes to break down lignin. However, there are limitations to biopulping that prevent it from outcompeting other pulping processes, such as requiring constant aeration and mixing.

The work presented in this dissertation investigates anaerobic bacteria as a promising alternative source for consolidated depolymerization of lignin and its conversion to valuable byproducts. We first ask if anaerobic aromatic metabolism is vertically inherited or horizontally transferred across bacteria. We analyzed seven out of the nine known central intermediate pathways. Of the seven, benzoyl-CoA metabolism had the strongest phylogenetic signal, suggesting vertical inheritance is the driver of its phylogenetic distribution. This information can be used in future studies to test if predictions can be made for uncharacterized taxa and anaerobic benzoyl-CoA related metabolism.

We also investigated the mechanisms of two uncharacterized isolates, Sodalis sp. strain 159R and Tolumonas lignolytica BRL6-1. Strain 159R contains many genes related to both aerobic and anaerobic aromatic metabolism but lacks extracellular enzymes for anaerobic lignin depolymerization. Conversely, strain BRL6-1 did not demonstrate lignin metabolism but instead relies on iron redox and organic radicals to potentially modify lignin structure under anoxic conditions. The electron exchange between iron, lignin, and BRL6-1 suggests a protein that acts as a chelator and redox molecule is the intermediate between the bacteria and substrate. The two isolates demonstrate the importance that lignin depolymerization and metabolism may be found separately in organisms and should be considered in future designs for anaerobic biopulping and lignin valorization to be a competitive process on the market.

DOI

https://doi.org/10.7275/ysjk-qs95

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