Bioluminescent sensors for detection of bioavailable Hg(II) in the environment

Biosensors for the detection of pollutants in the environment can complement analytical methods by distinguishing bioavailable from inert, unavailable forms of contaminants. By using fusions of the well-understood Tn21 mercury resistance operon (mer) with promoterless luxCDABE from Vibrio fischeri, we have constructed and tested three biosensors for Hg(II). Bioluminescence specified by pRB28, carrying merRo/pT, by pOS14, mediating active transport of Hg(II), and by pOS15, containing an intact mer operon, was measured in rich and minimal media. The highest sensitivities were achieved in minimal medium and were 1, 0.5, and 25 nM Hg(II) for pRB28, pOS14, and pOS15, respectively. The utility of the biosensors in natural waters was demonstrated with freshwater, rain, and estuarine samples supplemented with Hg(II). mer-lux carried by pRB28 and pOS14 responded to Hg(II) in mercury-contaminated water samples collected from a freshwater pond. Semiquantitative analyses based on light emission in samples collected from the inlet (analytically determined total mercury, approximately 20 nM) and outlet (total mercury, approximately 7 nM) of the pond showed bioavailable mercury at approximately 20 and 1 to 2 nM, respectively. Thus, the biosensors described here semiquantitatively detect bioavailable inorganic mercury (at a nanomolar to micromolar concentration range) in contaminated waters.