Synthetic Biology Approaches to Engineer Biosensors for Arsenic Detection in Groundwater: Application to Niger Delta and Sahel Communities in Nigeria

Arsenic contamination of groundwater is an underappreciated public health crisis in select Nigerian communities, particularly in areas with geogenic arsenic release in the Niger Delta and Sahel aquifer systems. Whole-cell biosensors exploiting prokaryotic arsenic-responsive transcriptional regulators offer low-cost, field-deployable alternatives to laboratory spectrometric methods. This dissertation engineers and validates novel synthetic biology-based whole-cell biosensors for sensitive arsenic detection in field groundwater samples from Nigeria. The ArsR/ArsB regulatory system from Escherichia coli K12 and a Bacillus subtilis ArsR ortholog were computationally redesigned using molecular docking (AutoDock Vina) and protein engineering to improve arsenic binding affinity. Engineered sensors were cloned into synthetic regulatory circuits driving GFP reporter expression, assembled in pSB1C3 BioBrick vectors, and expressed in chassis strains E. coli DH5-alpha and Bacillus subtilis 168. Biosensor performance was optimized in defined media, and field validation was performed using groundwater samples from 40 sites across Bayelsa State (Niger Delta) and Yobe State (Sahel). The engineered ArsR biosensor detected arsenic at concentrations as low as 0.8 ppb, below the WHO guideline of 10 ppb, with a dynamic linear range of 0.8-150 ppb. Field validation showed 91.3% agreement with concurrent ICP-MS measurements. In Niger Delta samples, 37.5% of groundwater sources exceeded the WHO guideline, while 62% of tested Yobe borehole sites exceeded threshold. Original contributions include the first computationally guided arsenic sensor protein redesign for Nigerian environmental monitoring and a modular cell-free extract adaptation enabling biosensor stability at 40 degrees Celsius ambient temperature. Keywords: synthetic biology, arsenic biosensor, ArsR, groundwater, Niger Delta and Sahel.