Anaerobic microorganisms play a key role in the biological mercury (Hg) cycle due to their ability to produce bioaccumulative neurotoxic methylmercury (MeHg). However, despite recent advances, how bacteria accumulate inorganic Hg [Hg(II)] prior to methylation is largely unknown. In this study, we applied Hg stable isotopes to measure changes in cellular compartments of Geobacter sulfurreducens and a nonmethylating mutant strain to investigate intracellular transport of Hg(II). Both strains accumulated intracellular Hg(II) that was lower in δ202Hg relative to dissolved extracellular Hg(II), demonstrating mass-dependent fractionation during uptake. Hg reduction by the mutant strain (50% Hg concentration loss in 24 h) resulted in higher δ202Hg values of cellular Hg than in wild-type cells. Further observations showed increasing δ202Hg values in dissolved extracellular MeHg and Hg(II) but decreasing δ202Hg values of intracellular Hg(II) in wild-type G. sulfurreducens suggesting that external Hg pools may be the proximate source of Hg for methylation in this bacterium. This investigation demonstrates that cellular uptake is comprised of multiple processes and transformations that influence Hg(II) prior to methylation, which can impart distinct isotopic signatures to Hg(II) and MeHg pools in the environment.
|Title||Tracing the uptake of Hg(II) in an iron-reducing bacterium using mercury stable isotopes|
|Authors||Yuwei Wang, Sarah E. Janssen, Jeffra K Schaefer, Nathan Yee, John R Reinfelder|
|Publication Subtype||Journal Article|
|Series Title||Environmental Science and Technology Letters|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Upper Midwest Water Science Center|