Voytek Mary A.

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Mary A.

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  • Preprint
    A ubiquitous thermoacidophilic archaeon from deep-sea hydrothermal vents
    ( 2006-05-19) Reysenbach, Anna-Louise ; Liu, Yitai ; Banta, Amy B. ; Beveridge, Terry J. ; Kirshtein, Julie D. ; Schouten, Stefan ; Tivey, Margaret K. ; Von Damm, Karen L. ; Voytek, Mary A.
    Deep-sea hydrothermal vents play an important role in global biogeochemical cycles, providing biological oases at the seafloor that are supported by the thermal and chemical flux from the Earth’s interior. As hot, acidic and reduced hydrothermal fluids mix with cold, alkaline and oxygenated seawater, minerals precipitate to form porous sulphide-sulphate deposits. These structures provide microhabitats for a diversity of prokaryotes that exploit the geochemical and physical gradients in this dynamic ecosystem. It has been proposed that fluid pH in the actively-venting sulphide structures is generally low (pH<4.5)2 yet no extreme thermoacidophile has been isolated from vent deposits. Culture-independent surveys based on rRNA genes from deep-sea hydrothermal deposits have identified a widespread euryarchaeotal lineage, DHVE23-6. Despite DHVE2’s ubiquity and apparent deep-sea endemism, cultivation of this group has been unsuccessful and thus its metabolism remains a mystery. Here we report the isolation and cultivation of a member of the DHVE2 group, which is an obligate thermoacidophilic sulphur or iron reducing heterotroph capable of growing from pH 3.3 to 5.8 and between 55 to 75°C. In addition, we demonstrate that this isolate constitutes up to 15% of the archaeal population, providing the first evidence that thermoacidophiles may be key players in the sulphur and iron cycling at deep-sea vents.
  • Preprint
    Methods for measuring denitrification : diverse approaches to a difficult problem
    ( 2005-07-15) Groffman, Peter M. ; Altabet, Mark A. ; Bohlke, John K. ; Butterbach-Bahl, Klaus ; David, Mark B. ; Firestone, Mary K. ; Giblin, Anne E. ; Kana, Todd M. ; Nielsen, Lars Peter ; Voytek, Mary A.
    Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2), is important to primary production, water quality and the chemistry and physics of the atmosphere at ecosystem, landscape, regional and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses and future prospects for the different methods. Methodological approaches covered include; 1) acetylene-based methods, 2) 15N tracers, 3) direct N2 quantification, 4) N2/Ar ratio quantification, 5) mass balance approaches, 6) stoichiometric approaches, 7) methods based on stable isotopes, 8) in situ gradients with atmospheric environmental tracers and 9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.