Active transport, substrate specificity, and methylation of Hg(II) in anaerobic bacteria

Jeffra K. Schaefer, Sara S. Rocks, Wang Zheng, Liyuan Liang, Baohua Gu, Francois M. M. Morel

Research output: Contribution to journalArticle

167 Scopus citations

Abstract

The formation of methylmercury (MeHg), which is biomagnified in aquatic food chains and poses a risk to human health, is effected by some iron- and sulfate-reducing bacteria (FeRB and SRB) in anaerobic environments. However, very little is known regarding the mechanism of uptake of inorganic Hg by these organisms, in part because of the inherent difficulty in measuring the intracellular Hg concentration. By using the FeRB Geobacter sulfurreducens and the SRB Desulfovibrio desulfuricans ND132 as model organisms, we demonstrate that Hg(II) uptake occurs by active transport. We also establish that Hg(II) uptake by G. sulfurreducens is highly dependent on the characteristics of the thiols that bind Hg(II) in the external medium, with some thiols promoting uptake and methylation and others inhibiting both. The Hg(II) uptake system of D. desulfuricans has a higher affinity than that of G. sulfurreducens and promotes Hg methylation in the presence of stronger complexing thiols. We observed a tight coupling between Hg methylation and MeHg export from the cell, suggesting that these two processes may serve to avoid the build up and toxicity of cellular Hg. Our results bring up the question of whether cellular Hg uptake is specific for Hg(II) or accidental, occurring via some essential metal importer. Our data also point at Hg(II) complexation by thiols as an important factor controlling Hg methylation in anaerobic environments.

Original languageEnglish (US)
Pages (from-to)8714-8719
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume108
Issue number21
DOIs
StatePublished - May 24 2011

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Mercury bioavailability
  • Mercury detoxification

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