Mercury Uptake by Desulfovibrio desulfuricans ND132: Passive or Active?

Recent studies have identified HgcAB proteins as being responsible for mercury [Hg­(II)] methylation by certain anaerobic microorganisms. However, it remains controversial whether microbes take up Hg­(II) passively or actively. Here, we examine the dynamics of concurrent Hg­(II) adsorption, uptake,...

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Bibliographic Details
Published in:Environmental science & technology 2019-06, Vol.53 (11), p.6264-6272
Main Authors: An, Jing, Zhang, Lijie, Lu, Xia, Pelletier, Dale A, Pierce, Eric M, Johs, Alexander, Parks, Jerry M, Gu, Baohua
Format: Article
Language:English
Subjects:
Anaerobic microorganisms
Bioavailability
Carbonyls
Cytoplasmic membranes
Deactivation
Desulfovibrio desulfuricans
ENVIRONMENTAL SCIENCES
Heat exchange
Inactivation
Mercury
Mercury (metal)
Mercury compounds
Metabolism
Methylation
Microorganisms
Proteins
Spheroplasts
Sulfate reduction
Thiols
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Summary:Recent studies have identified HgcAB proteins as being responsible for mercury [Hg­(II)] methylation by certain anaerobic microorganisms. However, it remains controversial whether microbes take up Hg­(II) passively or actively. Here, we examine the dynamics of concurrent Hg­(II) adsorption, uptake, and methylation by both viable and inactivated cells (heat-killed or starved) or spheroplasts of the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 in laboratory incubations. We show that, without addition of thiols, >60% of the added Hg­(II) (25 nM) was taken up passively in 48 h by live and inactivated cells and also by cells treated with the proton gradient uncoupler, carbonylcyanide-3-chlorophenylhydrazone (CCCP). Inactivation abolished Hg­(II) methylation, but the cells continued taking up Hg­(II), likely through competitive binding or ligand exchange of Hg­(II) by intracellular proteins or thiol-containing cellular components. Similarly, treatment with CCCP impaired the ability of spheroplasts to methylate Hg­(II) but did not stop Hg­(II) uptake. Spheroplasts showed a greater capacity to adsorb Hg­(II) than whole cells, and the level of cytoplasmic membrane-bound Hg­(II) correlated well with MeHg production, as Hg­(II) methylation is associated with cytoplasmic HgcAB. Our results indicate that active metabolism is not required for cellular Hg­(II) uptake, thereby providing an improved understanding of Hg­(II) bioavailability for methylation.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.9b00047