Particle-Bound Hg(II) is Available for Microbial Uptake as Revealed by a Whole-Cell Biosensor

Particle-bound mercury (HgP), ubiquitously present in aquaticenvironments, can be methylated into highly toxic methylmercury, but itremains challenging to assess its bioavailability. In this study, we developed anEscherichia coli-based whole-cell biosensor to probe the microbial uptake ofinorganic Hg(II) and assess the bioavailability of HgPsorbed on natural andmodel particles. This biosensor can quantitatively distinguish thecontribution of dissolved Hg(II) and HgPto intracellular Hg. Resultsshowed that the microbial uptake of HgPwas ubiquitous in the environment,as evidenced by the bioavailability of sorbed-Hg(II) onto particulate matterand model particles (Fe2O3,Fe3O4,Al2O3, and SiO2). In both oxic and anoxicenvironments, HgPwas an important Hg(II) source for microbial uptake,with enhanced bioavailability under anoxic conditions. The composition ofparticles significantly affected the microbial uptake of HgP, with higher bioavailability being observed for Fe2O3and lower for Al2O3particles. The bioavailability of HgPvaried also with the size of particles. In addition, coating with humic substances and modelorganic compound (cysteine) on Fe2O3particles decreased the bioavailability of HgP. Overall, ourfindings highlight the role of HgPin Hg biogeochemical cycling and shed light on the enhanced Hg-methylation in settling particles and sediments in aquatic environments

Automated summary

A biosensor based on Escherichia coli was developed to assess the bioavailability of particle-bound mercury (HgP). The results showed that HgP uptake by microorganisms was ubiquitous in both oxic and anoxic environments, with enhanced bioavailability under anoxic conditions.