Robust Mercury Methylation across Diverse Methanogenic Archaea

Methylmercury (MeHg) production was compared among nine cultured methanogenic archaea that contain , 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. , an 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 (except ) 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 several methanogens that had not previously been tested ( SANAE, , GKZPZ, and E1-9c). Maximal methylation was observed at low sulfide concentrations (