INDUCTION OF BACTERIAL MERCURY-RESPONSIVE AND COPPER-RESPONSIVE PROMOTERS - FUNCTIONAL DIFFERENCES BETWEEN INDUCIBLE SYSTEMS AND IMPLICATIONS FOR THEIR USE IN GENE-FUSIONS FOR IN-VIVO METAL BIOSENSORS

We have compared the induction by the cognate metal salts of two promo ters responsible for metal-resistance gene expression in bacteria. The mercuric ion resistance promoter, P-merTPAD of transposon Tn501 and t he copper resistance promoter, P-pcoE from plasmid pRJ1004 were separa tely cloned to express the lacZ gene under the regulation of their nor mal trans-acting elements. The lux genes of Vibrio fischeri were also expressed from P-merTPAD. The induction of P-merTPAD gave a hypersensi tive profile, as reported previously: the apparent Hill coefficient wa s 2.6 when using beta-galactosidase activity as a measure of lacZ gene expression. In contrast, the induction of P-pcoE was hyposensitive, w ith an apparent Hill coefficient of 0.63 for induction of beta-galacto sidase activity, and this map be related to the role of copper as an e ssential micronutrient. These response profiles suggest that transcrip tional fusions of the merTPAD promoter allow the construction of strai ns that are suitable for detecting threshold levels of mercuric ions, but not for accurate determinations of mercuric ion concentrations acr oss a wide range. In contrast, transcriptional fusions to the pcoE pro moter are well suited to determination of the concentrations of copper salts. The comparison of induction profiles of P-merTPSAD using lacZ or lux reporter genes, show different stimulus-response curves, probab ly due to differing instrument sensitivities. These results have pract ical implications in the construction of whole cell gene-fusion biosen sors for the detection and quantitation of heavy metals.