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

Particle-bound mercury (Hg P ), ubiquitously present in aquatic environments, can be methylated into highly toxic methylmercury, but it remains challenging to assess its bioavailability. In this study, we developed an Escherichia coli -based whole-cell biosensor to probe the microbial uptake of inorganic Hg(II) and assess the bioavailability of Hg P sorbed on natural and model particles. This biosensor can quantitatively distinguish the contribution of dissolved Hg(II) and Hg P to intracellular Hg. Results showed that the microbial uptake of Hg P was ubiquitous in the environment, as evidenced by the bioavailability of sorbed-Hg(II) onto particulate matter and model particles (Fe 2 O 3 , Fe 3 O 4 , Al 2 O 3 , and SiO 2 ). In both oxic and anoxic environments, Hg P was an important Hg(II) source for microbial uptake, with enhanced bioavailability under anoxic conditions. The composition of particles significantly affected the microbial uptake of Hg P , with higher bioavailability being observed for Fe 2 O 3 and lower for Al 2 O 3 particles. The bioavailability of Hg P varied also with the size of particles. In addition, coating with humic substances and model organic compound (cysteine) on Fe 2 O 3 particles decreased the bioavailability of Hg P . Overall, our findings highlight the role of Hg P in Hg biogeochemical cycling and shed light on the enhanced Hg-methylation in settling particles and sediments in aquatic environments.