Geobacteraceae are important members of mercury-methylating microbial communities of sediments impacted by waste water releases

• Published in: The ISME Journal Vol. 12; no. 3; pp. 802 - 812
• Main Authors: Bravo, Andrea G., Zopfi, Jakob, Buck, Moritz, Xu, Jingying, Bertilsson, Stefan, Schaefer, Jeffra K., Poté, John, Cosio, Claudia
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-03-2018; Nature Publishing Group
• Subjects: 631/326/171; 704/286; Aquatic environment; Bioaccumulation; Biomedical and Life Sciences; Communities; Deltaproteobacteria - genetics; Dimethylmercury; DNA methylation; DNA sequencing; Ecology; Ecotoxicology; Environmental factors; Evolutionary Biology; Food chains; Food webs; Gene sequencing; Geochemistry; Geologic Sediments - chemistry; Geologic Sediments - microbiology; Iron; Iron - analysis; Lakes; Lakes - microbiology; Life Sciences; Mercury; Mercury (metal); Mercury - metabolism; Methanogenic bacteria; Methylation; Methylmercury; Methylmercury Compounds - metabolism; Microbial activity; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Microorganisms; Neurotoxins; Next-generation sequencing; Organic matter; RNA, Ribosomal, 16S - analysis; rRNA 16S; Sediments; Sulfates; Sulfur; Sulfur - analysis; Toxicology; Waste Water - chemistry; Wastewater; Wastewater treatment; Wastewater treatment plants; Water Pollutants, Chemical - metabolism; Water treatment; Water treatment plants
• ISSN: 1751-7362; 1751-7370; 1751-7370
• DOI: 10.1038/s41396-017-0007-7

Microbial mercury (Hg) methylation in sediments can result in bioaccumulation of the neurotoxin methylmercury (MMHg) in aquatic food webs. Recently, the discovery of the gene
hgcA
, required for Hg methylation, revealed that the diversity of Hg methylators is much broader than previously thought. However, little is known about the identity of Hg-methylating microbial organisms and the environmental factors controlling their activity and distribution in lakes. Here, we combined high-throughput sequencing of 16S rRNA and
hgcA
genes with the chemical characterization of sediments impacted by a waste water treatment plant that releases significant amounts of organic matter and iron. Our results highlight that the ferruginous geochemical conditions prevailing at 1–2 cm depth are conducive to MMHg formation and that the Hg-methylating guild is composed of iron and sulfur-transforming bacteria, syntrophs, and methanogens.
Deltaproteobacteria
, notably
Geobacteraceae
, dominated the
hgcA
carrying communities, while sulfate reducers constituted only a minor component, despite being considered the main Hg methylators in many anoxic aquatic environments. Because iron is widely applied in waste water treatment, the importance of
Geobacteraceae
for Hg methylation and the complexity of Hg-methylating communities reported here are likely to occur worldwide in sediments impacted by waste water treatment plant discharges and in iron-rich sediments in general.