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Development of fluorescent whole-cell bacterial bioreporters for detection of inorganic arsenic and cadmium

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2019
Elçin, Evrim
Environmental heavy metal contamination in many regions of the world is a serious problem of ecological health. Fast and constant monitoring of their levels is significant for both preventing their accumulation and taking an immediate action for removal. As an alternative approach to standard laboratory techniques, various biosensor systems for detection of heavy metals have been proposed. Bacterial biosensors hold great promise for in-field detection of heavy metals. In this study, two different whole cell Escherichia coli bioreporter strains were developed for detection of inorganic arsenic and cadmium. In their presence, reporter gene expression increases which is detected as fluorescent signal later interpreted as a measure of available metal level in sample. Following cloning studies, arsenic and cadmium bacterial bioreporter strains were characterized for their metal specificity and detection limits by using different media and induction plans. In liquid assays, arsenic bioreporter could detect arsenite and arsenate at 10 μg/L after 2 hours, and cadmium bioreporter could detect cadmium of 2 μg/L after 1.5 hours of induction. Additionally, the arsenic bioreporter could estimate the bioavailable arsenic level in contaminated groundwater sample. To be integrated into a portable device, immobilization of arsenic bacterial bioreporter was investigated using agar and alginate biopolymers. Entrapment parameters of polymer concentration and cell density were evaluated. Immobilized cells were characterized for their metal specificity and detection limits by using different media. Agar and alginate immobilized bioreporter systems could detect arsenite and arsenate of 25 μg/L and 150 μg/L within 5 hours and 2 hours, respectively. The results demonstrated that these bacterial arsenic and cadmium bioreporter strains are applicable in determining the environmentally safe concentrations of these two most abundant heavy metals.