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.

Each year, more and more multi-drug resistant bacterial strains emerge, thus complicating treatment and increasing the average stay in the intensive care unit. As antibiotics are being rendered inefficient, there is a need to look into ways of weakening the internal state of bacterial cells to make them more susceptible to antibiotics. For this, we first need to understand what methods bacteria employ to fight against antibiotics. In this work, we have reviewed how bacteria respond to antibiotics. There is a similarity in response to antibiotic exposure and starvation (stringent stress) which changes the metabolic state. We have delineated what metabolism changes take place and how they are associated with oxidative stress. For example, there is a common change in NADH concentration that is tied to both metabolism and oxidative stress. Finally, we have compared the findings in literature with our research on an antibiotic-resistant RNA polymerase mutant that alters the gene expression profile in the general areas of metabolism and oxidative stress. Based on this thesis, we have suggested a couple of strategies to make antibiotics more efficient; however, as antibiotic-mediated killing is very complex, researchers need to delve deeper to understand and manipulate the full cellular response.