Particle-Bound Hg(II) is Available for Microbial Uptake as Revealed by a Whole-Cell Biosensor
Yuping Xiang, Yingying Guo, Guangliang Liu, Yanwei Liu, Maoyong Song, Jianbo Shi, Ligang Hu, Yongguang Yin, Yong Cai, Guibin Jiang
Abstract
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.