Date of Award

Fall 2020

Document Type

Undergraduate Honors Thesis

Degree Name

Bachelor of Arts in Biology




Dr. Terry Bird


Dr. Susannah Stern


Naturally found in soil and water environments arsenic is toxic to many organisms, carcinogenic to humans, and poses a significant public health risk. Yet communities of bacteria found thriving in arsenic ridden environments have evolved mechanisms to tolerate and exploit both oxidation states of this heavy metal (arsenite and arsenate). As the site of an old arsenic mine, Black Mountain Open Space Park in San Diego, California has yielded concentrations of arsenic in the soil between 111-14,800 ppm. Exceeding average arsenic soil concentrations and levels considered safe in the environment by the World Health Organization, we sought to characterize the phylogenetic diversity and mechanisms of arsenic resistance within the bacterial community living in the soils of the old mine site. 28 unique species of bacteria were isolated and characterized through a minimum inhibitory concentration experiment that assessed the level of bacterial arsenic resistance and a silver nitrate assay that examined the ability for the bacterial species to transform arsenic between its two naturally occurring oxidation states. Based on the results of these experiments, we found a highly diverse community of bacteria with eight species that also had arsenate reducing capabilities.