title: Aerobic Mercury-resistant bacteria alter Mercury speciation and retention in the Tagus Estuary (Portugal).
abstract: Aerobic mercury-resistant bacteria were isolated from the sediments of two highly mercury-polluted areas of the Tagus Estuary (Barreiro and Cala do Norte) and one natural reserve area (Alcochete) in order to test their capacity to transform mercury. Bacterial species were identified using 16S rRNA amplification and sequencing techniques and the results indicate the prevalence of Bacillus sp. Resistance patterns to mercurial compounds were established by the determination of minimal inhibitory concentrations. Representative Hg-resistant bacteria were further tested for transformation pathways (reduction, volatilization and methylation) in cultures containing mercury chloride. Bacterial Hg-methylation was carried out by Vibrio fluvialis, Bacillus megaterium and Serratia marcescens that transformed 2-8% of total mercury into methylmercury in 48h. In addition, most of the HgR bacterial isolates showed Hg(2+)-reduction andHg(0)-volatilization resulting 6-50% mercury loss from the culture media. In summary, the results obtained under controlled laboratory conditions indicate that aerobic Hg-resistant bacteria from the Tagus Estuary significantly affect both the methylation and reduction of mercury and may have a dual face by providing a pathway for pollution dispersion while forming methylmercury, which is highly toxic for living organisms.
authors.affiliation: Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
authors.forename: Neusa L
authors.initials: NL
authors.lastname: Figueiredo
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: João
authors.initials: J
authors.lastname: Canário
authors.affiliation: Department of Earth & Environmental Sciences, Acadia University, K.C. Irving Environmental Science Center, 32 University Avenue, Wolfville, Nova Scotia, Canada.
authors.forename: Nelson J
authors.initials: NJ
authors.lastname: O'Driscoll
authors.affiliation: Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
authors.forename: Aida
authors.initials: A
authors.lastname: Duarte
authors.affiliation: Research Institute for Medicines (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal. Electronic address: cristina.carvalho@ff.ulisboa.pt.
authors.forename: Cristina
authors.initials: C
authors.lastname: Carvalho
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004351:Drug Resistance; D063366:Estuaries; D019015:Geologic Sediments / Q000382:microbiology; D008628:Mercury / Q000378:metabolism* / Q000633:toxicity; D008767:Methylmercury Compounds / Q000378:metabolism* / Q000633:toxicity; D008826:Microbial Sensitivity Tests; D011174:Portugal; D012329:RNA, Bacterial / Q000032:analysis; D012336:RNA, Ribosomal, 16S / Q000032:analysis; D014835:Volatilization; D014874:Water Pollutants, Chemical / Q000378:metabolism* / Q000633:toxicity
chemical_list: D008767:Methylmercury Compounds; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Aerobic bacteria; Biogeochemistry; Estuaries; Estuarine chemistry; Mercury; Methylmercury