Sarah E. Janssen Jeffra K Schaefer Nathan Yee John R Reinfelder Yuwei Wang 2020 <p><span>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&nbsp;</span><i>Geobacter sulfurreducens</i><span>&nbsp;and a nonmethylating mutant strain to investigate intracellular transport of Hg(II). Both strains accumulated intracellular Hg(II) that was lower in δ</span>²⁰²<span>Hg 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 δ</span>²⁰²<span>Hg values of cellular Hg than in wild-type cells. Further observations showed increasing δ</span>²⁰²<span>Hg values in dissolved extracellular MeHg and Hg(II) but decreasing δ</span>²⁰²<span>Hg values of intracellular Hg(II) in wild-type&nbsp;</span><i>G. sulfurreducens</i><span>&nbsp;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.</span></p> application/pdf 10.1021/acs.estlett.0c00409 en American Chemical Society Tracing the uptake of Hg(II) in an iron-reducing bacterium using mercury stable isotopes article