Abstract

Plastics have become ubiquitous in modern life due to their low cost, lightweight nature, tunable properties, and durability. However, the accessibility of plastics during their functional lifetimes can also become a drawback at the end of life, owing to their highly recalcitrant nature, with almost 80% of the plastics produced ending up in landfills and leaking into the environment. The current plastic pollution crisis has stimulated research into state-of-the-art technologies for recycling and upcycling plastic waste. The combination of chemical degradation and bioconversion is a promising strategy, in which the chemically degraded products can be metabolized by various microorganisms to produce high-value compounds through an open-loop process. Recently, the exploitation of non-model microorganisms has emerged as a promising approach to waste upcycling due to their versatile metabolic capabilities that are either absent or poorly integrated in model bacteria. The goal of this dissertation is to develop genetic tools and elucidate unknown metabolic pathways in understudied non-model bacteria, and to demonstrate their application to the upcycling of plastic waste. In this work, genetic tools were developed for the non-model bacterium Rhodococcus jostii PET (hereafter RPET), including fluorescent reporters, endogenous promoters, inducible gene expression systems, and serine integrase-based recombinational tools for efficient genome editing. Using these tools, we systematically engineered the RPET strain to enhance production of the value-added bioproduct lycopene from poly(ethylene terephthalate) (PET) hydrolysates as feedstocks. Additionally, we elucidated the catabolic pathways for glutarate and pimelate in the non-model bacterium Acinetobacter baylyi ADP1 (hereafter ADP1) through RNA sequencing, phenotyping, and enzymatic assays. Employing rational metabolic engineering, the polyethylene (PE) deconstruction products were converted into lycopene as a proof-of-concept product in ADP1, thereby demonstrating the potential of this microbial chassis to upcycle post-consumer PE waste. Finally, we introduced a process that leverages a synthetic microbial consortium comprising RPET and ADP1 with an engineered division of labor. This robust consortium synergistically and efficiently metabolizes diverse mixtures of oxygenated compounds derived from the depolymerization of post-consumer, mixed plastic waste, regardless of fluctuations in waste composition. We assessed the upcycling potential of this consortium through rational metabolic engineering of both specialists, channeling these oxygenates into lycopene and lipids. Taken together, this work advances the application of non-model bacteria to valorize plastic waste for sustainable biomanufacturing, thereby providing an option to the global challenge of plastic pollution.

Committee Chair

Yinjie Tang

Committee Members

Fangqiong Ling; Himadri Pakrasi; Kimberly Parker; Sunkyu Park

Degree

Doctor of Philosophy (PhD)

Author's Department

Energy, Environmental & Chemical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

4-29-2026

Language

English (en)

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Available for download on Tuesday, June 15, 2027

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