Evaluating strategies for integrating bacterial cells into a biosensor designed to detect electrophilic toxins

Abstract

To improve the process stability of wastewater treatment plants, the construction of a whole-cell bacterial biosensor is explored to harness the natural stress response of the bacterial cells. The stress response selected in this work is the glutathione-gated potassium efflux (GGKE) system, which responds to electrophilic stress by effluxing potassium from the interior to the exterior of the cell. Thus, the bulk potassium in solution can be monitored as an indicator of bacterial stress. By utilizing this stress response in a biosensor, the efflux of potassium can be correlated to the stress response of the immobilized culture, providing an early warning system for electrophilic shock. This type of shock is a causative factor in many process upset events in wastewater treatment plants, so the application of the sensor would be an early warning device for such plants. The research conducted here focused on the biological element of the biosensor under development. Three immobilization matrices were explored to determine the cell viability and potassium efflux potential from immobilized cells: a calcium alginate, a photopolymer, and a thermally reversible gel. The calcium alginate was unstable, and dissolved after five days, such that the long-term impact of immobilization on the cells could not be determined in the matrix. The photopolymer resulted in very low actvity and viability of immobilized cellsOf the three matrices tested, indicating that the composition of the polymer was toxic to the cells. Of the matrices tested, the thermally-reversible gel showed the best response for further study, in that the matrix did not inhibit cell activity or potassium efflux.