Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy



Major Professor

Todd Reynolds

Committee Members

Elizabeth Fozo, Gladys Alexandre, Jennifer Debruyn


The development of plastic polymers has revolutionized modern society. These polymers are found ubiquitously in commodities and the production of these plastics is one of the most profitable industries in the world. However, the very characteristics that make plastics so universal and useful is also leading to detrimental ecological impacts. Due to their prevalence, finding novel microorganisms capable of breaking down these plastics is an important task. Another way these problems have are being addressed is by creating plastics that are more amenable to degradation. These plastics contain moieties more easily recognized by enzymes created by microbial life. Due to the increased adoption of these plastics, its important to understand their effect on the biology of microbial life.

In this dissertation we developed a biochemical assay to detect lactic acid that was being released as monomer from the biodegradable polymer polylactic acid due to bacterial degradation. We found a novel isolate of Bacillus pumilus (B12) that is capable of breaking down polylactic acid, with this degradation being able to robustly within 48 hours of incubation. Next we used our assay to observe how changing the nutrient composition allotted to B. pumilus B12 will alter its rate of PLA degradation. We saw increases in degradation when B. pumilus B12 was given maltose and mannitol as a sole carbon source, while observing decreases with adenine, potassium and phosphate supplementations. Next we used proteomic and transcriptomic tools to identify genes differentially expressed in conditions with altered PLA degradation. We found that in conditions with a lowered level of PLA degradation, genes associated with motility, chemotaxis and protein export are all downregulated.

Next, we investigated contamination found in a surfactant rich environment for novel bacteria capable of breaking down polyethylene and other recalcitrant carbon sources. We found six strains of novel Bacilli that were capable of growing on polysorbates, polyethylene glycol and mineral oil-rich in alkenes. Upon incubating one isolate of Bacillus megaterium with polyethylene films, we observed microbial growth, a lowered pH and a loss of tensile strength of the plastic. These two projects contribute new assays, bacterial isolates and insight to the field of polymer degradation.

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