There are few successful reports of successful use of gene-fusion biosensor in the monitoring of a metal toxicity in field application. These strains express a sensitive reporter gene, luciferase, connected to a promoter element responding specifically to various heavy metals. Inserting a heavy metal responsive element directionally cloned in a suitable vector in front of the luciferase gene by using standard recombinant-DNA techniques created all the sensor plasmids. Using a nucleotide database, one can isolate a promoter/operator element generated by a polymerase chain reaction using specific oligonucleotide primers. The plasmids can then be expressed in different hosts, in order to obtain maximal and specific response to each of the metal tested. For instance, Biomet sensors (patented and recognized by OVAM) used a relevant soil bacterium, Ralstonia metallidu-rans, to modify it to deliver a light reaction when specific heavy metals go into the cell. The quantification of light emissions can easily be done with a microtiter plate luminometer. Freeze-dried sensor cells were also tested used like reagents. Another bioluminescent sensor (mer-lux fusion) for detection of mercury was successfully used to examine the feasibility of testing mercury concentration of natural water from a contaminated freshwater pond .
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