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CC BY V4.0, Open Access
Dissertation
FUNDAMENTALS OF BIOCONVERSION OF BIOREFINERY WASTES TO LIPIDS BY RHODOCOCCUS STRAINS
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000005391
Handle:
https://hdl.handle.net/2376/119110
Abstract
Valorization of lignin-rich biorefinery wastes to biofuels and bioproducts is critical but challenging to improve overall carbon efficiency and facilitate the commercial viability of lignocellulose-based biorefinery. The goal of this dissertation is to understand the fundamentals of bioconversion of lignin and typical non-sugar compounds from biorefinery waste to lipids by Rhodococcus strains. The key contributions of this work include the development of a co-fermentation module employing natural and engineered Rhodococcus strains with significantly improved lignin degradation and/or lipid biosynthesis capacities, which enabled simultaneous conversion of glucose, lignin and its derivatives into lipids. 2D 1H-13C NMR analysis supported the degradation of lignin. Qualitative secretome analysis identified candidate ligninolytic enzymes and accessory oxidases. Global proteome profiles of strains uncovered the ring cleavage of lignin-derived aromatics potentially through a variety of routes to generate central metabolites, including phenylacetic acid pathway, homogentisate pathway and meta-cleavage of catechol, besides widely recognized β-ketoadipate pathway. In addition, R. jostii RHA1 showed excellent catabolic capacity to degrade various non-sugar compounds common in pretreated biomass hydrolysates, including vanillin, vanillate, furfural, 5-hydroxymethylfurfural, and acetate. Distinct utilization efficiency and selective contribution to lipid biosynthesis was observed when different carbon sources were fed. 1H NMR analysis revealed the oxidation pathway of furfural and 5-hydroxymethylfurfural which cannot be fully converted to central metabolites but promoted lipid production from benzoate, suggesting concealed regulatory mechanisms. On the other hand, up-regulation of proteins involved in oxidative stress response and fatty acid metabolism suggested imbalanced cellular redox status and deficiency of reducing power, pointing to a plausible explanation to low lipid yield of lignin conversion. To test this hypothesis, a new mass spectrometry-based proteomics workflow was developed to quantitatively compare protein abundances and redox states in Rhodococcus strains of lignin fermentation to that of glucose. Results showed the prevalence of redox-dependent regulation on metabolic network in response to available carbon sources and cellular redox states. Oxidative stress occurred using lignin as carbon source was proposed as a key barrier to obtain feasible lipid production. These results provide new angles and functional modules for strain metabolic engineering and facilitate the platform design of lignocellulose valorization.
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Details
- Title
- FUNDAMENTALS OF BIOCONVERSION OF BIOREFINERY WASTES TO LIPIDS BY RHODOCOCCUS STRAINS
- Creators
- Xiaolu Li
- Contributors
- Bin BY Yang (Advisor)Shulin SC Chen (Committee Member)John JHM Miller (Committee Member)Wei-Jun WQ Qian (Committee Member)Scott SEB Baker (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Biological Systems Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 197
- Identifiers
- 99900592055501842
- Language
- English
- Resource Type
- Dissertation