Author: Podar M, Gilmour CC, Brandt CC, Soren A, Brown SD, Crable BR, Palumbo AV, Somenahally AC, Elias DA.
Source: Science Advances.
Year: 2015
Comment: The authors state: "Therefore, it appears that the risk of Hg methylation in the human body by the endogenous microbiota is quite low but perhaps not zero."
Abstract / Excerpt:
Mercury (Hg) methylation produces the neurotoxic, highly bioaccumulative methylmercury (MeHg). The highly conserved nature of the recently identified Hg methylation genes hgcAB provides a foundation for broadly evaluating spatial and niche-specific patterns of microbial Hg methylation potential in nature. We queried hgcAB diversity and distribution in >3500 publicly available microbial metagenomes, encompassing a broad range of environments and generating a new global view of Hg methylation potential. The hgcAB genes were found in nearly all anaerobic (but not aerobic) environments, including oxygenated layers of the open ocean. Critically, hgcAB was effectively absent in ~1500 human and mammalian microbiomes, suggesting a low risk of endogenous MeHg production. New potential methylation habitats were identified, including invertebrate digestive tracts, thawing permafrost soils, coastal “dead zones,” soils, sediments, and extreme environments, suggesting multiple routes for MeHg entry into food webs. Several new taxonomic groups capable of methylating Hg emerged, including lineages having no cultured representatives. Phylogenetic analysis points to an evolutionary relationship between hgcA and genes encoding corrinoid iron-sulfur proteins functioning in the ancient Wood-Ljungdahl carbon fixation pathway, suggesting that methanogenic Archaea may have been the first to perform these biotransformations.
Citation: Podar M, Gilmour CC, Brandt CC, Soren A, Brown SD, Crable BR, Palumbo AV, Somenahally AC, Elias DA. Global prevalence and distribution of genes and microorganisms involved in mercury methylation. Science Advances. 2015; 1(9):e1500675.