Abstract: A genetic construct for use in a biosensor comprising: (a) a first nucleic acid molecule including a sequence encoding a reporter molecule having a detectable activity; and (b) a second nucleic acid molecule including a sequence encoding an enzyme which produces a substrate for the reporter molecule, the first sequence being under the control of a first inducible promoter and the second sequence being under the control of a second inducible promoter. A biosensor for measuring an environmental signal comprising a cell including the genetic construct and a means for measuring the activity of the reporter molecule in the cell when the cell has been exposed to the environmental signal.