Green fluorescent protein based whole cell bacterial biosensor for the detection of bioavailable heavy metals in soil environment

Abstract

A Green fluorescent protein (GFP) based whole cell bacterial biosensor was prepared using a bacterial strain sensitive to several heavy metals in order to detect bioavailable heavy metals in soils. The transformant, named as Bacillus megaterium VR1 was immobilized in silica matrix using sol–gel technology, and optimized for its effective pH range, cell density, exposure time, and storage stability. The lowest detection limit (LOD) for each metal was also determined. The pH range for the bacterial strain was found to be between pH 5–8.5. The optimum exposure time for the transformed bacterial strain to respond to the lowest tested concentration of heavy metal at 25% of inhibition compared to the control was determined as 4 h, 4 h, and 7 h, for Cd, Cu and Zn, respectively. SiNa/LUDOX 1/1 was selected as the optimum immobilization matrix. Storage up to 2 weeks did not show any reduction in the fluorescence in all the matrices. The linear range of the whole cell bacterial biosensor was determined as 0-10; 0–20 and 0–100 mg/L for Cd, Cu and Zn respectively. The lowest detection limit was determined as 1.42 × 10 −4 , 3.16 × 10 −4 , and 2.42 × 10 −4 mg/L for Cd, Cu and Zn, respectively. • Biosensor, Bacillus megaterium VR1 showed sensitivity to Cadmium, Copper, and Zinc. • The optimum pH for the biosensor was found to be pH 5–8.5. • Storage of biosensor up to 2 weeks did not show any decrease in fluorescence. • This biosensor has a great potential for monitoring heavy metal toxicity.