Date

Spring 2023

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Applied Environmental Science

Abstract

The overuse of pesticides in agricultural soils has been a long-discussed issue with implications for human health and optimal ecosystem functioning. These compounds may negatively affect non-target species and trophic webs that are otherwise harmless to crops. Various bacteria have been shown to have the capacity to metabolize pesticides, contributing to their remediation from the environment. In order to assess the community context for bacterial remediation of pesticides, we are characterizing soil bacteria communities that exist in agricultural-adjacent soils impacted by pesticide usage across Monterey County, CA.

We collected soil and water samples from fifteen sites exhibiting a range of land uses from May through November 2019 and performed pesticide tests using Abraxis ELISA kits for pyrethroids, organophosphates / carbamates, and imidacloprid. We isolated DNA from the samples with the Qiagen DNeasy soil/fecal microbe and water kits and amplified the 16S rRNA gene using the 319F and 806R primers as described in Fadrosh et al. 2014.

Through amplification of the 16S rRNA gene, we identified the bacterial species in the samples by matching bacterial sequences to online genetic databases for species identification. We sequenced amplicons on the Illumina MiSeq platform and processed the sequencing data to pair with the pesticide test results to determine how pesticide type and concentration may affect soil bacteria community diversity. The pesticide test results show predictably low / negligible readings from sites with non-agricultural land uses, with imidacloprid being the only detected pesticide in several of the agricultural sites in significant concentrations. We did not detect a decrease in overall species diversity in sites with greater imidacloprid concentrations, nor significant shifts in community structure. However, we identified key bacteria with pesticide-remediating capabilities in the agricultural sites that were not present in the natural sites.

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