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Applied and Environmental Microbiology, June 2000, p. 2430-2437, Vol. 66, No. 6
Skidaway Institute of Oceanography, Savannah, Georgia
314111; Advanced Analytical Center for
Environmental Sciences, Savannah River Ecology Laboratory, Aiken, South
Carolina 298022; Department of
Oceanography, Florida State University, Tallahassee, Florida
323063; and School of Civil and
Environmental Engineering, Georgia Institute of Technology,
Atlanta, Georgia 303324
Received 3 December 1999/Accepted 14 March 2000
Differences in methylmercury (CH3Hg) production
normalized to the sulfate reduction rate (SRR) in various species of
sulfate-reducing bacteria (SRB) were quantified in pure cultures and in
marine sediment slurries in order to determine if SRB strains which
differ phylogenetically methylate mercury (Hg) at similar rates.
Cultures representing five genera of the SRB (Desulfovibrio
desulfuricans, Desulfobulbus propionicus,
Desulfococcus multivorans, Desulfobacter sp.
strain BG-8, and Desulfobacterium sp. strain BG-33) were
grown in a strictly anoxic, minimal medium that received a dose of
inorganic Hg 120 h after inoculation. The mercury methylation
rates (MMR) normalized per cell were up to 3 orders of magnitude higher
in pure cultures of members of SRB groups capable of acetate
utilization (e.g., the family Desulfobacteriaceae) than in
pure cultures of members of groups that are not able to use acetate
(e.g., the family Desulfovibrionaceae). Little or no Hg
methylation was observed in cultures of Desulfobacterium or
Desulfovibrio strains in the absence of sulfate, indicating
that Hg methylation was coupled to respiration in these strains.
Mercury methylation, sulfate reduction, and the identities of
sulfate-reducing bacteria in marine sediment slurries were also
studied. Sulfate-reducing consortia were identified by using
group-specific oligonucleotide probes that targeted the 16S rRNA
molecule. Acetate-amended slurries, which were dominated by members of
the Desulfobacterium and Desulfobacter groups,
exhibited a pronounced ability to methylate Hg when the MMR were
normalized to the SRR, while lactate-amended and control slurries had
normalized MMR that were not statistically different. Collectively, the
results of pure-culture and amended-sediment experiments suggest that
members of the family Desulfobacteriaceae have a greater
potential to methylate Hg than members of the family Desulfovibrionaceae have when the MMR are normalized to the
SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in
marine sediments that are rich in organic matter and dissolved sulfide
rapid CH3Hg accumulation is coupled to rapid sulfate
reduction. The observations described above have broad implications for
understanding the control of CH3Hg formation and for
developing remediation strategies for Hg-contaminated sediments.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Sulfate-Reducing Bacteria Methylate Mercury at
Variable Rates in Pure Culture and in Marine Sediments
*
Corresponding author. Mailing address: Department of
Oceanography, Florida State University, Tallahassee, FL 32306-4320. Phone: (850) 645-3334. Fax: (850) 644-2581. E-mail:
jkostka{at}ocean.fsu.edu.
Applied and Environmental Microbiology, June 2000, p. 2430-2437, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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