Abstract
Microbial conversion of inorganic mercury (IHg) to methylmercury (MeHg) is a significant environmental concern because of the bioaccumulation and biomagnification of toxic MeHg in the food web. Laboratory incubation studies have shown that, despite the presence of large quantities of IHg in cell cultures, MeHg biosynthesis often reaches a plateau or a maximum within hours or a day by an as yet unexplained mechanism. Here we report that mercuric Hg(II) can be taken up rapidly by cells of Desulfovibrio desulfuricans ND132, but a large fraction of the Hg(II) is unavailable for methylation because of strong cellular sorption. Thiols, such as cysteine, glutathione, and penicillamine, added either simultaneously with Hg(II) or after cells have been exposed to Hg(II), effectively desorb or mobilize the bound Hg(II), leading to a substantial increase in MeHg production. The amount of thiol-desorbed Hg(II) is strongly correlated to the amount of MeHg produced (r = 0.98). However, cells do not preferentially take up Hg(II)−thiol complexes, but Hg(II)−ligand exchange between these complexes and the cell-associated proteins likely constrains Hg(II) uptake and methylation. We suggest that, aside from aqueous chemical speciation of Hg(II), binding and exchange of Hg(II) between cells and complexing ligands such as thiols and naturally dissolved organics in solution is an important controlling mechanism of Hg(II) bioavailability, which should be considered when predicting MeHg production in the environment.
| Original language | English |
|---|---|
| Pages (from-to) | 13335-13341 |
| Number of pages | 7 |
| Journal | Environmental Science and Technology |
| Volume | 50 |
| Issue number | 24 |
| DOIs | |
| State | Published - Dec 20 2016 |
Funding
We thank Xiangping Yin for her assistance with the mercury and methylmercury analyses. This research was sponsored by the U.S. Department of Energy (DOE) Office of Science, Office of Biological and Environmental Research, as part of the Mercury Science Focus Area at Oak Ridge National Laboratory (ORNL), which is managed by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with DOE. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doepublic-access-plan). Y.L. was supported in part by the Chinese Scholarship Council (CSC) of China.