Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Civil Engineering


Jean MacRae

Second Committee Member

Willem Brutsaert

Third Committee Member

Gregory D. Mayer


Arsenic in groundwater and private wells used for drinking water is a public health concern in the USA and abroad. Bacteria may influence arsenic cycling by altering arsenic's redox state, thus affecting the mobility and toxicity of arsenic species in groundwater. In 2002 a bacterial strain (NP4) was isolated from water drawn from a 30m depth in a well at Northport, Maine (McCaffery, 2002). This well has a known history of high arsenic levels (1446 pg/L). Sequencing of the isolate confirmed that NP4 is a unique bacterial strain closely related to two other arsenate reducers in the subgroup SuIfurospirillum (SES3 and MIT13). This study sought to further investigate the rates of arsenate reduction by these organisms and evaluate the role and significance of arsenate reduction in NP4's growth. To further characterize the NP4 strain the use of different carbon sources and terminal electron acceptors were also investigated. Concentrations of the reactants and products were measured over time using ion exchange high performance liquid chromatography. Cell growth was monitored by direct counts, and gas chromatography was used to monitor headspace composition. Controls included media without inoculate, and inoculated media without a carbon source or arsenate. In the presence of NP4, arsenate and lactate concentrations decreased with a corresponding increase in cell density, arsenite and acetate concentrations. Growth was also observed when selenate, Fe(III), Mn(IV), nitrate and some sulfur compounds were used as electron acceptors. No growth was observed when sulfate was used as an electron acceptor.