Development of a broad-spectrum fluorescent heavy metal bacterial biosensor

Bacterial biosensors can measure pollution in terms of their actual toxicity to living organisms. A recombinant bacterial biosensor has been constructed that is known to respond to toxic levels of Zn(2+), Cd(2+) and Hg(2+). The zinc regulatory gene zntR and zntA promoter from znt operon of E. coli have been used to trigger the expression of GFP reporter protein at toxic levels of these ions. The sensor was induced with 3-800 ppm of Zn(2+), 0.005-4 ppm of Cd(2+) and 0.001-0.12 ppm of Hg(2+) ions. Induction studies were also performed in liquid media to quantify GFP fluorescence using fluorimeter. To determine the optimum culture conditions three different incubation periods (16, 20 and 24 h) were followed. Results showed an increased and consistent fluorescence in cells incubated for 16 h. Maximum induction for Zn(2+), Cd(2+) and Hg(2+) was observed at 20, 0.005 and 0.002 ppm, respectively. The pPROBE-zntR-zntA biosensor reported here can be employed as a primary screening technique for aquatic heavy metal pollution.