Robust Mercury Methylation across Diverse Methanogenic Archaea
ABSTRACT. Methylmercury (MeHg) production was compared among nine cultured methanogenic archaea that containhgcAB, a gene pair that codes for mercury (Hg) methylation. The methanogens tested produced MeHg at inherently different rates, even when normalized to growth rate and Hg availability. Eight of the nine tested were capable of MeHg production greater than that of spent- and uninoculated-medium controls during batch culture growth.Methanococcoides methylutens, anhgcAB+strain with a fused gene pair, was unable to produce more MeHg than controls. Maximal conversion of Hg to MeHg through a full batch culture growth cycle for each species (exceptM. methylutens) ranged from 2 to >50% of the added Hg(II) or between 0.2 and 17 pmol of MeHg/mg of protein. Three of the species produced >10% MeHg. The ability to produce MeHg was confirmed in severalhgcAB+methanogens that had not previously been tested (Methanocella paludicolaSANAE,Methanocorpusculum bavaricum,Methanofollis liminatansGKZPZ, andMethanosphaerula palustrisE1-9c). Maximal methylation was observed at low sulfide concentrations (<100 μM) and in the presence of 0.5 to 5 mM cysteine. ForM. hollandica, the addition of up to 5 mM cysteine enhanced MeHg production and cell growth in a concentration-dependent manner. As observed for bacterial Hg methylators, sulfide inhibited MeHg production. An initial evaluation of sulfide and thiol impacts on bioavailability showed methanogens responding to Hg complexation in the same way as doDeltaproteobacteria. The mercury methylation rates of several methanogens rival those of the better-studied Hg-methylating sulfate- and iron-reducing Deltaproteobacteria. IMPORTANCE. Archaea, specifically methanogenic organisms, play a role in mercury methylation in nature, but their global importance to MeHg production and the subsequent risk to ecosystems are not known. Methanogenesis has been linked to Hg methylation in several natural habitats where methylmercury production incurs risk to people and ecosystems, including rice paddies and permafrost. In this study, we confirm that most methanogens carrying thehgcABgene pair are capable of Hg methylation. Finally, we found that methylation rates vary inherently amonghgcAB+methanogens but that several species are capable of MeHg production at rates that rival those of the better-know Hg-methylating sulfate- and iron-reducing bacteria. Methanogens may need to be considered equally with sulfate and iron reducers in evaluations of MeHg production in nature.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1461239
- Alternate ID(s):
- OSTI ID: 1435231
- Journal Information:
- mBio (Online), Vol. 9, Issue 2; ISSN 2150-7511
- Publisher:
- American Society for MicrobiologyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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