A chromosomally based luminescent bioassay for mercury detection in red soil of China

A luminescent reporter gene system was constructed by fusing the mercury-inducible promoter, P ( merT ), and its regulatory gene, merR, with a promoterless reporter gene EGFP. A stable and nonantibiotic whole-cell reporter (BMB-ME) was created by introducing the system cassette into the chromosome of Pseudomonas putida strain and then applied it for mercury detection in the red soil of China. Spiked with 10 and 100 microg g(-1) Hg(2+) and after 15 and 30 days incubation, soil samples were extracted and evaluated water soluble, bioavailable, organic matter bound, and residual fractions of mercury by both BMB-ME and chemical way. The expression of EGFP was confirmed in soil extraction, and fluorescence intensity was quantified by luminescence spectrometer. The sensor strain BMB-ME appeared to have a detection range similar to that of reversed-phase high-performance liquid chromatography method. The optimal temperature for EGFP expression was 35 degrees C and the lowest detectable concentration of Hg(2+) 200 nM. Cu(2+), Fe(2+), Mn(2+), Sn(2+), Zn(2+), Co(2+), Ag(+), Ba(2+), Mg(2+), and Pb(2+) ions at nanomolar level did not interfere with the measurement. These results showed that the BMB-ME constitute an adaptable system for easy sensing of small amounts of mercury in the red soil of China.