title: Mercury methylation and sulfate reduction rates in mangrove sediments, Rio de Janeiro, Brazil: The role of different microorganism consortia.
abstract: Recent studies have shown Hg methylation in mangrove sediments, however, little is known about the different microorganism consortia involved. We investigated the participation of prokaryotes in general, iron-reducing bacteria-IRB, sulfate-reducing bacteria-SRB, methanogens and fungi in Hg methylation and sulfate reduction rates (SRR) in mangrove sediments using iron amendments for IRB and specific inhibitors for the other microorganisms. Sediment samples were collected from two mangrove zones, tidal flat and mangrove forest (named root sediments). Samples were incubated with203Hg or35SO42-and Me203Hg/35Sulfur were measured by liquid scintillation. Methylmercury (MeHg) formation was significantly reduced when SRB (87.7%), prokaryotes (76%) and methanogens (36.5%) were inhibited in root sediments, but only SRB (51.6%) and prokaryotes (57.3%) in tidal flat. However, in the tidal flat, inhibition of methanogens doubled Hg methylation (104.5%). All inhibitors (except fungicide) significantly reduced SRR in both zones. In iron amended tidal flat samples, Hg methylation increased 56.5% at 100 μg g-1and decreased at 500 and 1000 μg g-1(57.8 and 82%). In the roots region, however, MeHg formation gradually decreased in response to Fe amendments from 100 μg g-1(37.7%) to 1000 μg g-1(93%). SRR decreased in all iron amendments. This first simultaneous evaluation of Hg methylation and sulfate-reduction and of the effect of iron and inhibitors on both processes suggest that SRB are important Hg methylators in mangrove sediments. However, it also suggests that SRB activity could not explain all MeHg formation. This implies the direct or indirect participation of other microorganisms such as IRB and methanogens and a complex relationship among these groups.
authors.affiliation: Laboratório de Traçadores Wolfgang C. Pfeiffer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Bloco G/CCS/Ilha do Fundão, Rio de Janeiro, RJ, CEP: 21941-902, Brazil. Electronic address: raquel@biof.ufrj.br.
authors.forename: Raquel Rose Silva
authors.initials: RRS
authors.lastname: Correia
authors.affiliation: Laboratório de Traçadores Wolfgang C. Pfeiffer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Bloco G/CCS/Ilha do Fundão, Rio de Janeiro, RJ, CEP: 21941-902, Brazil. Electronic address: jeanrdg@biof.ufrj.br.
authors.forename: Jean Remy Davée
authors.initials: JRD
authors.lastname: Guimarães
mesh_terms: D001938:Brazil; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology; D007501:Iron / Q000737:chemistry; D008628:Mercury / Q000032:analysis* / Q000737:chemistry; D008745:Methylation; D008767:Methylmercury Compounds / Q000032:analysis* / Q000737:chemistry; D059013:Microbial Consortia; D010084:Oxidation-Reduction; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D013431:Sulfates / Q000737:chemistry; D016999:Sulfur-Reducing Bacteria / Q000254:growth & development; D053833:Wetlands
chemical_list: D008767:Methylmercury Compounds; D012989:Soil Pollutants; D013431:Sulfates; D007501:Iron; D008628:Mercury
keywords: Fungi; Iron-reducing bacteria; Liquid scintillation; Methanogens; Radiotracer; Sulfate-reducing bacteria