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Arsenites

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Joanne M. Santini – 1st expert on this subject based on the ideXlab platform

  • Microbial oxidation of arsenite in a subarctic environment: diversity of arsenite oxidase genes and identification of a psychrotolerant arsenite oxidiser.
    BMC Microbiology, 2010
    Co-Authors: Thomas H. Osborne, Heather E. Jamieson, Karen A. Hudson-edwards, D. Kirk Nordstrom, Stephen R. Walker, Seamus A. Ward, Joanne M. Santini

    Abstract:

    Background: Arsenic is toxic to most living cells. The two soluble inorganic forms of arsenic are arsenite (+3) and arsenate (+5), with arsenite the more toxic. Prokaryotic metabolism of arsenic has been reported in both thermal and moderate environments and has been shown to be involved in the redox cycling of arsenic. No arsenic metabolism (either dissimilatory arsenate reduction or arsenite oxidation) has ever been reported in cold environments (i.e. < 10°C). Results: Our study site is located 512 kilometres south of the Arctic Circle in the Northwest Territories, Canada in an inactive gold mine which contains mine waste water in excess of 50 mM arsenic. Several thousand tonnes of arsenic trioxide dust are stored in underground chambers and microbial biofilms grow on the chamber walls below seepage points rich in arsenite-containing solutions. We compared the arsenite oxidisers in two subsamples (which differed in arsenite concentration) collected from one biofilm. ‘Species’ (sequence) richness did not differ between subsamples, but the relative importance of the three identifiable clades did. An arsenite-oxidising bacterium (designated GM1) was isolated, and was shown to oxidise arsenite in the early exponential growth phase and to grow at a broad range of temperatures (4-25°C). Its arsenite oxidase was constitutively expressed and functioned over a broad temperature range. Conclusions: The diversity of arsenite oxidisers does not significantly differ from two subsamples of a microbial biofilm that vary in arsenite concentrations. GM1 is the first psychrotolerant arsenite oxidiser to be isolated with the ability to grow below 10°C. This ability to grow at low temperatures could be harnessed for arsenic bioremediation in moderate to cold climates.

  • Protein Film Voltammetry of Arsenite Oxidase from the Chemolithoautotrophic Arsenite-Oxidizing Bacterium NT-26†
    Biochemistry, 2006
    Co-Authors: Paul V. Bernhardt, Joanne M. Santini

    Abstract:

    The chemolithoautotrophic bacterium NT-26 (isolated from a gold mine in the Northern Territory of Australia) is unusual in that it acquires energy by oxidizing arsenite to arsenate while most other arsenic-oxidizing organisms perform this reaction as part of a detoxification mechanism against the potentially harmful arsenite [present as As(OH)3 at neutral pH]. The enzyme that performs this reaction in NT-26 is the molybdoenzyme arsenite oxidase, and it has been previously isolated and characterized. Here we report the direct (unmediated) electrochemistry of NT-26 arsenite oxidase confined to the surface of a pyrolytic graphite working electrode. We have been able to demonstrate that the enzyme functions natively while adsorbed on the electrode where it displays stable and reproducible catalytic electrochemistry in the presence of arsenite. We report a pH dependence of the catalytic electrochemical potential of −33 mV/pH unit that is indicative of proton-coupled electron transfer. We also have performed ca…

  • Arsenite oxidation by the heterotroph Hydrogenophaga sp. str. NT-14: the arsenite oxidase and its physiological electron acceptor.
    Biochimica et biophysica acta, 2004
    Co-Authors: Rachel N Vanden Hoven, Joanne M. Santini

    Abstract:

    Heterotrophic arsenite oxidation by Hydrogenophaga sp. str. NT-14 is coupled to the reduction of oxygen and appears to yield energy for growth. Purification and partial characterization of the arsenite oxidase revealed that it (1). contains two heterologous subunits, AroA (86 kDa) and AroB (16 kDa), (2). has a native molecular mass of 306 kDa suggesting an alpha(3)beta(3) configuration, and (3). contains molybdenum and iron as cofactors. Although the Hydrogenophaga sp. str. NT-14 arsenite oxidase shares similarities to the arsenite oxidases purified from NT-26 and Alcaligenes faecalis, it differs with respect to activity and overall conformation. A c-551-type cytochrome was purified from Hydrogenophaga sp. str. NT-14 and appears to be the physiological electron acceptor for the arsenite oxidase. The cytochrome can also accept electrons from the purified NT-26 arsenite oxidase. A hypothetical electron transport chain for heterotrophic arsenite oxidation is proposed.

Enrica Canzi – 2nd expert on this subject based on the ideXlab platform

  • Arsenite Oxidation in Ancylobacter dichloromethanicus As3-1b Strain: Detection of Genes Involved in Arsenite Oxidation and CO2 Fixation
    Current Microbiology, 2012
    Co-Authors: Vincenza Andreoni, Raffaella Zanchi, Lucia Cavalca, Anna Corsini, Cristina Romagnoli, Enrica Canzi

    Abstract:

    The aim of this study was to characterize a facultative chemolithotrophic arsenite-oxidizing bacterium by evaluating the growth and the rate of arsenite oxidation and to investigate the genetic determinants for arsenic resistance and CO2 fixation. The strain under study, Ancylobacter dichloromethanicus As3-1b, in a minimal medium containing 3 mM of arsenite as electron donor and 6 mM of CO2–bicarbonate as the C source, has a doubling time (td) of 8.1 h. Growth and arsenite oxidation were significantly enhanced by the presence of 0.01 % yeast extract, decreasing the t d to 4.3 h. The strain carried arsenite oxidase (aioA) gene highly similar to those of previously reported arsenite-oxidizing Alpha-proteobacteria. The RuBisCO Type-I (cbbL) gene was amplified and sequenced too, underscoring the ability of As3-1b to carry out autotrophic As(III) oxidation. The results suggest that A. dichloromethanicus As3-1b can be a good candidate for the oxidation of arsenite in polluted waters or groundwaters.

  • Arsenite oxidation in Ancylobacter dichloromethanicus As3-1b strain: Detection of genes involved in arsenite oxidation and CO 2 fixation
    Current Microbiology, 2012
    Co-Authors: Vincenza Andreoni, Raffaella Zanchi, Lucia Cavalca, Anna Corsini, Cristina Romagnoli, Enrica Canzi

    Abstract:

    The aim of this study was to characterize a facultative chemolithotrophic arsenite-oxidizing bacterium by evaluating the growth and the rate of arsenite oxidation and to investigate the genetic determinants for arsenic resistance and CO 2 fixation. The strain under study, Ancylobacter dichloromethanicus As3-1b, in a minimal medium containing 3 mM of arsenite as electron donor and 6 mM of CO 2 -bicarbonate as the C source, has a doubling time (t d ) of 8.1 h. Growth and arsenite oxidation were significantly enhanced by the presence of 0.01 % yeast extract, decreasing the t d to 4.3 h. The strain carried arsenite oxidase (aioA) gene highly similar to those of previously reported arsenite-oxidizing Alpha-proteobacteria. The RuBisCO Type-I (cbbL) gene was amplified and sequenced too, underscoring the ability of As3-1b to carry out autotrophic As(III) oxidation. The results suggest that A. dichloromethanicus As3-1b can be a good candidate for the oxidation of arsenite in polluted waters or groundwaters. © 2012 Springer Science+Business Media, LLC.

Rachel N. Vanden Hoven – 3rd expert on this subject based on the ideXlab platform

  • Arsenite oxidation by the heterotroph Hydrogenophaga sp. str. NT-14: the arsenite oxidase and its physiological electron acceptor
    Biochimica et Biophysica Acta, 2004
    Co-Authors: Rachel N. Vanden Hoven, Joanne M. Santini

    Abstract:

    Abstract Heterotrophic arsenite oxidation by Hydrogenophaga sp. str. NT-14 is coupled to the reduction of oxygen and appears to yield energy for growth. Purification and partial characterization of the arsenite oxidase revealed that it (1) contains two heterologous subunits, AroA (86 kDa) and AroB (16 kDa), (2) has a native molecular mass of 306 kDa suggesting an α3β3 configuration, and (3) contains molybdenum and iron as cofactors. Although the Hydrogenophaga sp. str. NT-14 arsenite oxidase shares similarities to the arsenite oxidases purified from NT-26 and Alcaligenes faecalis, it differs with respect to activity and overall conformation. A c-551-type cytochrome was purified from Hydrogenophaga sp. str. NT-14 and appears to be the physiological electron acceptor for the arsenite oxidase. The cytochrome can also accept electrons from the purified NT-26 arsenite oxidase. A hypothetical electron transport chain for heterotrophic arsenite oxidation is proposed.

  • Molybdenum-Containing Arsenite Oxidase of the Chemolithoautotrophic Arsenite Oxidizer NT-26
    Journal of Bacteriology, 2004
    Co-Authors: Joanne M. Santini, Rachel N. Vanden Hoven

    Abstract:

    The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an α2β2 configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per α2β2 unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of Alcaligenes faecalis, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of Aeropyrum pernix, Sulfolobus tokodaii, and Chloroflexus aurantiacus. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome bc1 and b6f complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an aroA mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate.