An extended range whole-cell tetracycline biosensor strain was constructed by insertion of the tet(M) gene, encoding tetracycline resistance by ribosomal protection, into plasmid pTGFP2, which contains a transcriptional fusion between a tetracycline regulated promoter and the green fluorescent protein gene. Tetracycline, oxytetracycline, chlortetracycline and minocycline all effectively induced the resulting Escherichia coli MC4100/pTGM biosensor and similar dose–response characteristics were recorded by flow cytometry for all four compounds. The novel tetracycline biosensor was responsive to drug concentrations ranging from below 5ngml −1 to 16μgml −1 , which represents a significant improvement of the original version.