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Robust Mercury Methylation across Diverse Methanogenic Archaea
Cynthia C Gilmour1, Allyson L Bullock2, Alyssa McBurney2
1Smithsonian Environmental Research Center, Edgewater, Maryland, USA gilmourc@si.edu.
Mbio
|April 12, 2018
Summary
Most methanogenic archaea carrying the hgcAB gene pair can produce methylmercury (MeHg). Their production rates vary, with some rivaling those of bacteria, highlighting archaea's role in environmental MeHg levels.
Area of Science:
- Microbiology
- Environmental Science
- Biogeochemistry
Background:
- Methanogenic archaea are crucial in anaerobic environments.
- Mercury methylation by archaea is increasingly recognized but not fully quantified.
- The hgcAB gene pair is essential for mercury methylation.
Purpose of the Study:
- To compare methylmercury (MeHg) production rates among diverse cultured methanogenic archaea.
- To investigate the influence of growth conditions on MeHg production.
- To confirm MeHg production capabilities in previously untested methanogen species.
Main Methods:
- Culturing nine methanogenic archaea strains with hgcAB genes.
- Measuring MeHg production rates under controlled batch culture conditions.
- Analyzing the impact of sulfide and cysteine concentrations on methylation.
Main Results:
- Eight of nine tested methanogens produced significant MeHg, with rates varying inherently.
- Methanococcoides methylutens (hgcAB-negative) showed no significant MeHg production.
- Methylation rates ranged from 2% to >50% conversion, with some species exceeding 10% MeHg.
- Optimal methylation occurred at low sulfide (<100 μM) and moderate cysteine (0.5–5 mM).
- Methanogen methylation rates rivaled those of sulfate- and iron-reducing bacteria.
Conclusions:
- Most hgcAB-positive methanogens are capable of methylmercury production.
- Inherent differences in methylation rates exist among methanogen species.
- Methanogens are significant contributors to environmental methylmercury, comparable to bacteria.
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