Construction Of Cd～(2+)-Biosensor Based On Gfp-Tagged Strain And Detection For Cadmium Toxicity

gfp-tagged plasmid was transformed into two heavy metal-resistant bacterial strains.The luminescence quantitative method of gfp-tagged strains and the application ofbiosensor in detection of cadmium toxicity were studied. This study includes constructionof gfp-tagged engineered strains, characterization of the relation between cadmium ionconcentration and fluorescence intensity, and the detection of cadmium toxicity byluminescence method.Plasmid with CadR-EGFP tag was transformed to E. coli, and differentconcentrations of cadmium was added to induce egpf gene expression. Fluorescenceintensity is enhanced with increased promoter efficiency in the presence of less than 0.05mM cadmium. When cadmium concentration was in the range of 0.05～0.15 mM,fluorescence intensity was influenced by both bacterial biomass and promoter efficiency,and a "bell" curve was observed. When cadmium concentration was above 0.15 mM,fluorescence intensity was mainly dependent on bacterial biomass, with a steadyfluorescence intensity at the stationary phase.The fluorescence of E. coli (pHQ21) as influenced by soil particles was exmined.Fluorecence intensity was decreased by 80% in the system of montmorillonite andkaolinite. No significant influence was found on fluorescence intensity for sand andgoethite systems.CadR-EGFP marked Enterobacter aerogenes NTG01 and putita pseudomonas X4,and X4 was used in pot culture experiments with tobacco and Cd²⁺ polluted soil. Strongfluorescence signal was observed by fluorescence microscope, showing that the X4biosensor can detect Cd²⁺ pollution from soil. The growth of tobacco was enhanced in thetreatment of X4 strain as compared with no-biosensor treatment. The results suggestedthat the biosensor may also have potentials in the remediation of heavy metal pollutedsoils.