Bacterial mercury resistance from atoms to ecosystems

Abstract

Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.

Linkage between community diversity of sulfate-reducing microorganisms and methylmercury concentration in paddy soil

“…This result was different from the previous studies based on short-term incubation experiments showing a negative influence of Hg pollution on the abundance of microorganism Zhou et al 2012). These different effects could be attributed to their different polluted duration by Hg, and some microbial groups in soil might exhibit some resistance or adaptation to long-term Hg stress (Barkay et al 2003). For each site, total abundances of the dsrAB gene in 0-40 cm soil were significantly higher than those in the 40-80 cm soil (P<0.05).…”

Patterns of Bacterial Diversity Along a Long-Term Mercury-Contaminated Gradient in the Paddy Soils

“…Similar patterns were found in the order of Anaerolineales, envOPS12, SBR1031, and Hydrogenophilales, whose abundances increased with elevated THg and MeHg concentrations. A previous study suggested that the Hg resistance gene (merA), responsible for tolerance to inorganic Hg 2+ , was mainly distributed in Proteobacteria, Actinobacteria and Firmicutes [16], as well as in archeal groups [55]. Nevertheless, our results might imply that the merA gene is more widely distributed in the other microbial groups, because less impact of Hg on these Hgresistant-like bacteria (e.g.…”

“…For example, inorganic Hg 2+ in environments can be reduced to volatile Hg 0 by Hg-resistant bacteria [16]. The resistance of bacteria to inorganic Hg 2+ is associated with the presence of the Hg resistance gene (merA) [16,17], which has been considered widely distributed in the phyla of Firmicutes, Actinobacteria and Proteobacteria [16].…”

“…For example, inorganic Hg 2+ in environments can be reduced to volatile Hg 0 by Hg-resistant bacteria [16]. The resistance of bacteria to inorganic Hg 2+ is associated with the presence of the Hg resistance gene (merA) [16,17], which has been considered widely distributed in the phyla of Firmicutes, Actinobacteria and Proteobacteria [16]. Meanwhile, ionic Hg in anaerobic habitats may also be potentially methylated to highly toxic methylmercury (MeHg) by Hg-methylating microbes [18,19], such as sulphate-reducing bacteria (SRB) [20,21], iron-reducing bacteria (FeRB) [22,23] and methanogens [24,25].…”

“…We covered a THg gradient from 1.11 to 29.07 mg kg −1 in the paddy soils around the Hg mining area [16]. Bar-coded pyrosequencing targeting 16S rRNA genes was used to explore the diversity and structure of the bacterial communities in the soils.…”