Expanding Primary Metabolism for New Bioproducts: Pathway Design, Enzyme Discovery, and Fermentation Optimization

Abstract

Fermentation, like brewing beer, has the potential to produce chemicals and fuels that are currently derived from petroleum via unsustainable and environmentally-unfriendly manufacturing processes. The two main challenges for a fermentation-based chemical industry are the diversity of molecules and the effectiveness of conversion processes. To enable broader applications of fermentation, there is a pressing need to expand the scope of fermentation products and improve the relevant production efficiency. Therefore, my thesis research focuses on expanding the capabilities of microbial biosynthesis in Escherichia coli. I designed novel metabolic pathways to enable the production of new bioproducts and to effectively convert abundant but underused biomass sugars into value-added chemicals. The biosynthetic processes were realized by enzyme discovery and then further optimized by metabolic engineering and enzyme engineering. Firstly, I designed and built a medium-chain ester biosynthetic platform and enabled production of two target esters by screening the key enzyme. I also engineered a novel nonphosphorylative metabolism which can effectively convert biomass-derived pentoses or sugar acids into TCA cycle derivatives. Two chemicals, 1,4-butanediol and mesaconate, were successfully produced as demonstrations. Furthermore, an optically active monomer (-)-β-methyl-δ-valerolactone was manufactured via a chemo-enzymatic process and the key enzymes were investigated. Overall, this work has brought new tools and design principles to the field of metabolic engineering and can be served as the cornerstone for future development of economically feasible renewable chemicals.