Whole cell bacterial bioreporters are bacteria specifically engineered to react to the presence of chemical signals with the production of an easily quantifiable marker protein. In most cases, an existing regulatory system in the bacterial cell is exploited to drive expression of a specific reporter gene, such as bacterial luciferase, green fluorescent protein, beta-galactosidase or others. This is achieved by fusing the DNA for a promoterless reporter gene to an extra copy of the selected regulatable promoter and introducing this construction into the bacterial cell. Regulatory systems that have been applied include those for heavy metal resistancies (to obtain heavy metal responsive sensors), for organic compound degradation (to obtain organic compound sensors), and for cellular stress responses (to obtain general toxicity sensors).
Most whole-cell bacterial bioreporters are applied by incubating the cells in aqueous solution with the target compound(s) and analyzing the activity of the reporter protein (i.e., the reporter signal) after a previously calibrated induction period. Concentrations of the target chemical in unknown samples are inferred by comparing the reporter signal to that with a series of standard concentrations and incubated under exactly the same conditions. The reporter signal is usually only proportional to the target chemical within a specific concentration range. At higher target concentrations, the sensor output becomes saturated or even diminishes because of toxic effects to the sensor cells.
In principle it is also possible to have bacterial bioreporters measuring volatile compounds in the gas phase. Bioreporters expressing the green fluorescent protein can be used to measure the bioavailability of target chemicals to single cells. Current projects in our group focus on phenanthrene bioavailability, on development of new protocols for working with arsenic biosensors, on creating multisensor platforms and on mutagenizing regulatory proteins to obtain more and other effector recognition specificities.