GFP expressing bacterial biosensor to measure lead contamination in aquatic environment

A bacterial biosensor is reported that responds to Pb²⁺ in the range of 50-400 μM by expressing green fluorescence protein (GFP). The genetic element that senses Pb²⁺ includes the regulatory protein gene (PbrR) along with operator/promoter (PbrO/P) of the lead resistance operon from plasmid pMOL30. PbrO/P also controls the gfp reporter gene expression. Escherichia coli DH5α is the host organism. GFP response to induction by Pb²⁺ peaked at 250 μM. Decline in fluorescence beyond 250 μM was related to drop in copy number of the biosensor plasmid in the cells. A formula that estimates available Pb²⁺ concentration in test samples with 95% accuracy was derived by multiple regression of fluorescence and cell density values at various Pb²⁺ concentrations at 12 h growth. The biosensor was tested for co-inducibility by Cd²⁺, Zn²⁺ and Hg²⁺. Only Zn²⁺ showed mild induction at high concentrations and the highest fluorescence obtained was 8.5 times lower than that obtained with Pb²⁺. The induction method used here allows water collected from natural resources to be directly tested by using it to prepare the growth medium for the biosensor. This biosensor offers a simple and quick method for detection of available lead in the aquatic environment.