Use Of Cd²⁺-specific Biosensor Based On EGFP-tagged For The Monitoring Of The Cadmium-contaminated Soil

In this study, a Cd²⁺-specific biosensor was constructed using enhanced green fluorescent protein （EGFP） as reporter gene and Pseudomonas putida X4 as host strain. Its application for monitoring Cd²⁺ in cadmium-polluted soils was evaluated.The fluorescence performance of the biosensor is observed when growing in Luria-Bertani medium with 2 mmol/L Cd²⁺. The intensity of fluorescence of X4 biosensor enhanced with the increase of induction time. The biosensor specifically responded to Cd²⁺, and other ions, Zn²⁺, Pb²⁺,Co²⁺ and Cu²⁺ at 100 nmol/L - 10 mmol/L level did not interfere with the measurement by the biosensors. The biosensor showed no difference in the growth curve compared with wild type strain. When it was induced by Cd²⁺ with a concentration from 0 to 1 mmol/L, the fluorescence intensity was determined by the progiciency of the promoter. When it was exposed to more than 1 mmol/L Cd²⁺, the fluorescence was determined by the concentration of the biosensor cells. The fluorescence intensity kept stable when the strains got into stable-phase.Pot culture experiments with biosensor strains, pakchoi and Cd²⁺ polluted soils showed that the fluorescence trend was the same as the pure culture experiment. The X4 biosensor can dynamically monitor Cd²⁺ pollution from soil, which was also proved by RT-PCR. CFU and FCM experiments showed that the X4 biosensor strains successfully survived in nature soil. Since the Cd uptake by plant was declined, the existence of X4 biosensor strains reduced the toxicity of Cd²⁺and then improved growth of the plant. Our results demonstrate that the EGFP-tagged bacterial biosensor is useful and applicable in reflecting the cadmium pollution level in soil and suggests a potential for its inexpensive application in situ biroremendiation.