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Title: Mechanisms of Hg(II) uptake and methylation in methylating bacteria

The goal of this project was to understand the critical factors which control the availability and transport of Hg(II) into cells, a first step in the production of the neurotoxin, methylmercury. Specifically, this research focused on understanding the mechanism of bacterial mercury uptake and how mercury speciation affects the specificity and kinetics of mercury transport. Our research has shown that Hg(II) uptake in three different iron and sulfate-reducing proteobacteria occurs by the following mechanism (1) : Hg(II) uptake is an active transport process requiring energy, (2) it is dependent upon the structure of the Hg binding ligand, and (3) it is mediated by a heavy metal transporter such as one which transports the essential metal, Zn(II). In order to determine whether this mechanism extends to more diverse phylogenetic groups, we have begun examining Hg(II) uptake and bioavailability in two representative Hg methylating strains within the Firmicutes. These organisms have remarkably different membrane structures distinct from the Proteobacteria. Our results show low uptake rates in these two species of Firmicutes relative to the previously characterized Proteobacteria. This may explain the low methylation rates and yields observed in these organisms. Most surprisingly, however, these organisms appear to take up Hg(II) passively, asmore » the addition of a protonophore failed to reduce Hg(II) uptake in these organisms. This is quite different to what has been observed previously for the Proteobacteria and suggests a different mechanism for Hg(II) uptake in the Firmicutes. We are continuing to understand and describe Hg(II) uptake in these organisms. A manuscript is expected to be submitted on this research in June 2016.« less
  1. Princeton Univ., NJ (United States). Geosciences Dept.
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Technical Report
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Related Information: Manuscripts Published: Szczuka, F. M. M. Morel, and J. K. Schaefer. 2015. The effect of thiols, zinc, and redox conditions on Hg uptake in Shewanella oneidensis. Environ. Sci. Technol. 49: 7432-7438.J. K. Schaefer, A. Szczuka, and F. M. M. Morel. 2014. Effect of divalent metals on Hg(II) uptake and methylation by bacteria. Environ. Sci. Technol. 48: 3007-3013.J. K. Schaefer, R.-M. Kronberg, F. M. M. Morel, U. Skyllberg. 2014. Detection of a key Hg methylation gene, hgcA, in wetland soil. Environ. Microbiol. Rep. 6: 441-447.J. K. Schaefer, S. S. Rocks, W. Zheng, L. Liang, B. Gu, and F. M. M. Morel. 2011. Active transport, substrate specificity, and methylation of Hg(II) in anaerobic bacteria. Proc. Nat. Acad. Sci. 108: 8714-8719.Manuscripts In Preparation:S. Janssen and J. K. Schaefer. Mercury uptake and methylation in firmicutes. Submission planned to ES&T Lett.
Research Org:
Princeton Univ., NJ (United States)
Sponsoring Org:
USDOE Savannah River Operations Office (SRO)
Country of Publication:
United States