A Comparison of MER::LUX Whole Cell Biosensors And Moss, A Bioindicator, For Estimating Mercury Pollution

Abstract

A sensor responsive to Hg2+ (pDL20) was constructed by fusing part of a narrow spectrum mer operon, including its regulatory elements, to promoterless lux genes. This was compared with another mer::lux fusion (pRB28) in order to estimate the available Hg in moss, a conventional bioindicator used for surveying Hg pollution in terrestrial environments. Hg(II) was measured as the relative luminescence unit (RLU) emitted by E. coli cells carrying either pRB28 or pDL20. The linearity ranges of standard curves were measured by spiking HgCl2 at different nanomole levels in a phosphate buffered solution (PBS). The level of correlation between RLU and spiked HgCl2 depended on the incubation time of E. coli cells: the correlation factors (R2) of the regression lines were highly significant only after 150 min of incubation. pDL20 detected Hg(II) concentrations in the linear range between 0.05 nM and 0.5 nM and was approximately 27 times more sensitive than pRB28. The latter was less sensitive and showed a different range of linearity, from 20 nM to 200 nM. Measurements of bioavailable Hg were performed in buffered solutions leached from moss. Concentrations of Hg(II) were determined by external standard addition of HgCl2. pDL20 was found to be more reliable than pRB28 in the estimation of very low concentrations of bioavailable Hg (II). Both sensors were unable to determine Hg(0) emitted by geothermal activities.