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

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Proceedings of the National Academy of Sciences

DOI:https://doi.org/10.1073/pnas.1105781108· OSTI ID:1017329

Schasfer, Jeffra ^[1]; Rocks, Sara ^[1]; Zheng, Wang ^[2]; Liang, Liyuan ^[2]; Gu, Baohua ^[2]; Morel, Francois M ^[2]

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1. Princeton University
2. ORNL

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.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1017329
• Journal Information: Proceedings of the National Academy of Sciences, Journal Name: Proceedings of the National Academy of Sciences Journal Issue: 21 Vol. 108; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
AFFINITY
BACTERIA
DESULFOVIBRIO
EXPORTS
FOOD CHAINS
IRON
METHYLATION
METHYLMERCURY
Mercury SFA
SPECIFICITY
SUBSTRATES
SULFATE-REDUCING BACTERIA
THIOLS
TOXICITY
TRANSPORT