CELL-DENSITY-DEPENDENT SENSITIVITY OF A MER-LUX BIOASSAY

The sensitivity of a previously described assay (O. Selifonova, R. Bur lage, and T. Barkay, Appl. Environ. Microbiol. 59:3083-3090, 1993) for the detection of bioavailable inorganic mercury (Hg2+) by the activat ion of a mer-lux fusion was increased from nanomolar to picomolar conc entrations by reducing biomass in the assays from 10(7) to 10(5) cells ml(-1). The increase in sensitivity was due to a reduction in the num ber of cellular binding sites that may compete with the regulatory pro tein, MerR, for binding of the inducer, Hg2+. These results show that (i) the sensitivity of the mer-lux assay is sufficient for the detecti on of Hg2+ in most contaminated natural waters and (ii) mer-specified reactions, Hg2+ reduction and methylmercury degradation, can be induce d in natural waters and may participate in the geochemical cycling of mercury.