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- Genre: Doctoral Dissertation
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Polymers have played a pivotal role in building modern society. Polymers can be classified as synthetic and natural polymers. Accumulation of both synthetic and natural polymer waste leads to environmental pollution. This dissertation aims at developing one-pot bioprocesses for a breakdown of natural polymers like cellulose, and hemicellulose and synthetic polymers like polyethylene terephthalate (PET). First, a one-pot process was developed for hemicellulose breakdown. A signal peptide library of native SEC pathway signal peptides was developed for efficient secretion of endoxylanse enzyme. Furthermore, in situ, the process was successfully created for hemicellulose to xylose with the highest reported xylose titer of 7.1 g/L. In addition, E. coli: B. subtilis coculture bioprocess was developed to produce succinate, ethanol, and lactate from hemicellulose in one pot process.
Second, a one-pot process was developed for cellulose breakdown. In vitro enzyme assays were used to select SEC pathway signal peptides for endoglucanase and glucosidase secretion. Then, the breakdown of carboxymethyl cellulose (CMC), a cellulose derivative, was conducted in in situ conditions. U-13C fingerprinting study showed carbon enrichment from CMC when cultures were cofed with CMC and [U-13C] glucose. Further, Whatman filter paper sheets showed a change in shape in recombinant cocultures. SEM images showed continuous orientation in the case of two enzymes confirmed by fast Fourier transform (FFT), suggesting higher crystallinity of residues. Similarly, in microcrystalline cellulose breakdown in in situ conditions, a 72% reduction of avicel cellulose was achieved in a one pot bioprocess. SEM images revealed valleys and crevices on residues of coculture compared to smoother surfaces in monoculture residues pressing the importance of the synergistic activity of enzymes.
Finally, one pot deconstruction process was developed for synthetic polymer PET. First, the PET hydrolase secretion strain was developed by selecting a signal peptide library. The first bis(2-hydroxyethyl) terephthalate (BHET) consolidated bioprocess was developed, which produced a terephthalic acid titer of 7.4 g/L. PET breakdown was successfully demonstrated in in vitro conditions with a TPA titer of 4 g/L. Furthermore, PET breakdown was successfully demonstrated in in situ conditions. Consolidated bioprocesses can be an invaluable approach to waste utilization and making cost-effective processes.
ContributorsMhatre, Apurv (Author) / Varman, Arul (Thesis advisor) / Nielsen, David (Committee member) / Misra, Rajeev (Committee member) / Nannenga, Brent (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2023