A Luminescence-Based Mercury Biosensor

A new biosensor for the determination of bioavailable mercury is presented. It utilizes firefly luciferase gene as a reporter under the control of the mercury-inducible mer promoter from transposon Tn21 and Escherichia coli MC1061 as a host organism. The luminescence-based sensor was evaluated for the selectivity and sensitivity of the detection of mercury. The lowest detectable concentration of mercury was 0.1 tM. Cadmium, zinc, cobalt, copper and manganese ions did not interfere with the measurement even at millionfold concentrations compared to mercury. The results were in agreement with the results obtained by a mercury-independent luciferase expressing strain which acted as a control strain measuring total toxicity. The measurement of the bioavailability of metals is quite difficult with traditional analytical methods. The bioavailability of a metal is a very important factor in the determination of a metal toxicity,' and therefore, the detection of bioavailable metals is of great interest. Biosensors provide a promising way to assess bioavailability of different substances in the environment2 Microbes offer a cornucopia for the construction of biosensors for monitoring the status of the environment. Numerous unspecific sensors that react to any kind of toxic substance have been developed.2 A novel approach for a microbial biosensor is to connect a strictly regulated promoter to a sensitive reporter gene. The most interesting promoters for environmental analysis are found in bacteria that survive in environments contaminated by, for example, heavy metals or organic compounds. The ability of the bacteria to survive in a contaminated environment is usually based on a genetically encoded resistance system, the expression of which is regulated very preci~ely.~ Some biosensors using the promoter-reporter gene concept have been developed, for example, for the detection of mercws5 and xenobiotic com pound^.^^^ However, these approaches have been limited by the lack of sensitivity (parts per trillion, pptr) required for a biosensor that is intended to be used as an early warning system.