Detection and quantification of tetracyclines by whole cell biosensors

Three different mini-Tn5 plasmids, containing a tetracycline-inducible promoter, P-tet and a regulatory gene, tetR, in operon fusions with a reporter gene system (lacZYA, luxCDABE or gfp), were constructed. These biosensor constructs responded to low levels of tetracyclines by producing beta-galactosidase, light or green fluorescent protein. They did so in a quantitative manner, thus enabling the quantification of tetracyclines in the immediate surroundings of the biosensor organism. All three constructs were transferred successfully to different Gramnegative bacteria by conjugation. An Escherichia coli strain containing the P-tet-lac construct was used to determine oxytetracycline in milk as a demonstration of the application of these biosensors. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.