Whole cell- and protein-based biosensors for the detection of bioavailable heavy metals in environmental samples

Abstract

The principal goal of this work was to establish the feasibility of two biosensor technologies with enhanced specificity and selectivity for the detection of several bioavailable heavy metals in environmental samples. Two parallel strategies have been followed. The first approach was to construct whole cell bacterial biosensors that emit a bioluminescent or fluorescent signal in the presence of a biologically available heavy metal. The molecular basis of σ-54 promoters as sensing elements of environmental pollutants has been determined and a number of metal-induced promoter regions have been identified, sequenced and cloned as promoter cassettes. The specificity of the promoter cassettes has been determined using luxCDABE reporter systems. Whole cell-biosensors containing metal-induced lux reporter systems have been incorporated into different matrices for their later immobilisation on optic fibres and characterised in terms of their sensitivity and storage capacity. The second type of sensors was based on the direct interaction between metal-binding proteins and heavy metal ions. In this case, the capacitance changes of the proteins, such as synechoccocal metallothionein (as a GST-SmtA fusion protein) and the mercury regulatory protein, MerR, were detected in the presence of femtomolar to millimolar metal ion concentrations.