HR: 0800h
AN: B31A-0955    [Abstracts]
TI: Microbial arsenic oxidation in a shallow marine hydrothermal vent system
AU: * Amend, J P
EM: amend@wustl.edu
AF: Washington University, Dept. Earth and Planetary Sciences, St. Louis, MO 63130 United States
AU: Meyer-Dombard, D R
EM: darmeyer@artsci.wustl.edu
AF: Washington University, Dept. Earth and Planetary Sciences, St. Louis, MO 63130 United States
AU: Pichler, T
EM: pichler@shell.cas.usf.edu
AF: University of South Florida, Dept. Geology, Tampa, FL 33620 United States
AU: Price, R
EM: reprice@mail.usf.edu
AF: University of South Florida, Dept. Geology, Tampa, FL 33620 United States
AU: Herndon, E
EM: emherndo@artsci.wustl.edu
AF: Washington University, Dept. Earth and Planetary Sciences, St. Louis, MO 63130 United States
AU: Hsia, N
EM: nhsia@wustl.edu
AF: Washington University, Dept. Earth and Planetary Sciences, St. Louis, MO 63130 United States
AB: The toxic effects of arsenic are well documented, but this Group V element can also serve as an energy source to a diverse group of microorganisms. Most of the attention has been on arsenate (AsV) reduction, but the focus is shifting to include arsenite (AsIII) oxidation and subsequent immobilization through coprecipitation with iron (oxy)hydroxides. The shallow marine hydrothermal fluids near Ambitle Island, Papua New Guinea are characterized by arsenite concentrations of up to 1,000 μg/L. Directly proximal to the vent orifices, arsenate coprecipitates with 2-line ferrihydrite, coating rocks and corals in red and green biofilms up to 1 cm thick. DNA extracted from these coatings was amplified with archaeal- and bacterial-specific primers, and the 16S rRNA gene was sequenced. Both biofilm samples revealed archaeal communities exclusively composed of uncultured Crenarchaea. The bacterial members are primarily gamma Proteobacteria and Planctomycetes in the red biofilm, but 60% of the community in the green biofilm affiliate with the alpha Proteobacteria and candidate group OP11; there is minimal overlap in bacterial phylotypes between the two coatings. Slurries from these coatings were also used to inoculate geochemically designed growth media supplemented with various redox couples, including aerobic and anaerobic As(III) oxidation. On a medium targeting anaerobic, chemolithoautotrophic arsenic oxidation coupled to ferric iron reduction at 50 °C, predominantly rod-shaped organisms (~5×10⁵ cells/ml) were enriched. In contrast, on an aerobic arsenic oxidation medium, coccoid-shaped organisms (~3×10⁶ cells/ml) were enriched. The respective thermophilic microbial communities may be taking advantage of overall metabolisms represented by H₃AsO₃(aq) + 2FeOOH(s) + 3H⁺ = H₂AsO₄^- + 2Fe²⁺ + 3H₂O (1) and H₃AsO₃(aq) + 1/2O₂(aq) = H₂AsO₄^- + H⁺. (2) To date, no arsenite oxidizers are known to use ferric iron as a terminal electron acceptor (reaction 1). However, this environment, where arsenite-laden vent waters flow past mineral surfaces that can serve both as physical template and as oxidant, may be ideal for these putative organisms. On the other hand, a number of aerobic arsenite oxidizers have been described, especially among the bacteria, and reaction (2) is likely to support a microbial community involved in the oxidation and subsequent precipitation of arsenic.
DE: 0400 BIOGEOSCIENCES
SC: Biogeosciences [B]
MN: Fall Meeting 2005