Date of Award

Spring 5-5-2017

Document Type



Health Sciences


Helena, MT gets over 50% of its drinking water from Tenmile Creek. With a rich mining history, over 100 abandoned hard-rock mines have introduced arsenic into this aquatic ecosystem. The presence of arsenic may contribute to a change in bacteria community composition. The objective of this research was to detect changes in overall microbial diversity in response to arsenic concentrations. Sediment grabs were collected from ten different sites; three controls (/kg As), three mid-level arsenic concentrations (100-200 mg/kg As), and four high-level arsenic concentrations (250-6000 mg/kg As). Sediment from each site was plated on different media containing As III and As V. Bacterial colonies were picked from plates and identified using 16S gene sequencing (Macrogen USA, Rockville, MD), then compared to GenBank Database using NCBI BLAST. The community DNA was also extracted directly from sediments using a Power Soil Kit MoBio (Carlsbad, CA) and Next Generation Sequencing was performed at the University of Colorado Health Sciences Center (Lozupone Lab). Culturable species from each site were identified from 16S colony pick sequencing. The sequencing showed that Cyanobacteria streptophyta and Proteobacteria acidiphilium species were dominant in mid-level and high-level arsenic environments, and Cyanobacteria tramenophiles was a dominant species in the control environments. The Next Generation Sequencing showed a shift in high arsenic environments and high arsenic levels explained around 60% of the community differences. Arsenic caused a community change in diversity, as arsenic increased diversity in bacterial genera decreased.