Date

Fall 2025

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Applied Environmental Science

Abstract

Insecticides pose a threat to ecological, wildlife and human health when they are carried in runoff water from agricultural fields to surface and ground waters. Microbial bioremediation provides a promising avenue for degrading and removing these pollutants from runoff water before they dissipate into downstream ecosystems. While effective bioremediators for various target pesticides have been identified, we do not yet understand exactly how microbes degrade insecticides in most cases. In this study, I examined three bacterial strains with the ability to metabolize imidacloprid (strain Imidl Y) or malathion (strains Mal4 and Mal6), both common insecticides, and used transposon-mediated mutagenesis to answer the question of which genes are essential for this ability. I introduced the tn5 transposon to the study strains to create libraries of random knockout mutants, and subjected these mutants to selective conditions in order to eliminate any bacteria that lost the ability to metabolize insecticide. I then sequenced and mapped mutation sites in this selected population, identifying unmutated genes as essential for metabolism of insecticide. I identified 1603 conditionally essential genes for growth on insecticide in Mal6, 252 in Mal4, and 18 in Imid1 Y. Identifying these genes helps us understand the metabolic pathways used by these microbes when metabolizing insecticide. It also gives us a framework for future functional genomics work in these and other microbes. All of this will help us understand the evolution and diversity of insecticide metabolism and help design safe and effective systems to remediate insecticide pollution, making agricultural runoff water safer for ecological and public health.

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