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PI-Submitted Research Highlights for
Subsurface Biogeochemical Research Program

A Novel Iron-Loving Bacterium from the Deep Subsurface

Kenneth M. Kemner
Argonne National Laboratory

Highlight

16 February 2017

New research has uncovered the bacterium Orenia metallireducens, a microorganism from two kilometers deep underground capable of reducing iron.

The Science
A novel microorganism capable of withstanding high temperatures and briny water was isolated from a geological formation located two kilometers deep within the Illinois Basin. This bacterium, dubbed Orenia metallireducens, has many distinctive properties that allow it to reduce iron minerals such as goethite and hematite. These findings expand our knowledge of how bacteria survive in the deep, hostile environments of the terrestrial subsurface and provide further insights into how life might exist on other planetary bodies.

The Impact
The discovery of O. metallireducens expands our knowledge of the metabolic diversity of bacteria that inhabit the subsurface. Previously thought to be largely sterile, we now know that microbial life dwells deep within the fractures and pore spaces of rocks that make up the Earth’s crust. These bacteria drive many of the biogeochemical cycles that occur within the subsurface, driving the dissolution and precipitation of minerals as well as the breakdown of organic matter. Understanding the microbially-driven mechanisms behind these geochemical transformations is essential for parameterizing Earth system models that seek to quantify the flux of carbon between the atmosphere, soil, and subsurface.

Summary
The microbial reduction of ferric iron minerals is widespread in both terrestrial and marine environments and is potentially one of the earliest forms of metabolisms to evolve on Earth. Due to the abundance of ferric minerals in the Earth’s crust, Fe(III) reduction is of global environmental significance, particularly in the subsurface where it contributes to water quality, contaminant fate and transport, and the biogeochemical cycling of carbon. Taking groundwater that was sampled from two kilometers deep underground, we isolated a novel member of the phylum Firmicutes, named Orenia metallireducens strain Z6. We found O. metallireducens to have a number of unique properties, including the ability to reduce ferric iron minerals across a broad range of temperature, pH, and salinity. O. metallireducens also lacks the c-type cytochromes that are typically present in bacteria capable of reducing ferric iron such as Geobacter and Shewanella species. We also found that O. metallireducens is the only member of the order Halanaerobiales that is capable of reducing crystalline iron minerals such as goethite and hematite. The results of this study significantly expand the scope of phylogenetic affiliations, metabolic capabilities, and catalytic mechanisms that are known for iron-reducing microorganisms.

Contacts (BER PM)
Dr. Roland F. Hirsch
Program Officer, U.S. DOE Office of Science
roland.hirsch@science.doe.gov; (301) 903-9009

(PI Contact)
Dr. Kenneth M. Kemner
Argonne National Laboratory
kemner@anl.gov; (630) 252-1163

Funding
This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory, which is supported by the DOE Subsurface Biogeochemical Research Program, Office of Biological and Environmental Research, Office of Science. Use of the Electron Microscopy Center at Argonne and the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at Argonne was performed under Contract DE-AC02-06CH11357. This work, including the efforts of Yiran Dong, Robert A. Sanford, Randall A. Locke, Jr., and Bruce W. Fouke, was funded by U.S. Department of Energy (DOE) (DE-FC26-05NT42588). Parts of this work, including the efforts of Yiran Dong, Robert A. Sanford, Janet Y. Chang, and Bruce Fouke, was also funded by National Aeronautics and Space Administration (NASA) (NNA13AA91A).

Publication
Yiran Dong, Robert A. Sanford, Maxim I. Boyanov, Kenneth M. Kemner, Theodore M. Flynn, Edward J. O’Loughlin, Yun-Juan Chang, Randall A. Locke Jr., Joseph R. Weber, Sheila M. Egan, Roderick I. Mackie, Isaac Cann, and Bruce W. Fouke (2016). “Orenia metallireducens sp. nov. strain Z6, a novel metal-reducing member of the phylum Firmicutes from the deep subsurface.” Applied and Environmental Microbiology,Vol. 82 (21), pp. 6440–6453. doi: 10.1128/aem.02382-16.

Related Links
Subsurface Science Scientific Focus Area at Argonne National Laboratory

Article (PDF):
Appl. Environ. Microbiol.-2016-Dong-6440-53.pdf

This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory, which is supported by the DOE Subsurface Biogeochemical Research Program, Office of Biological and Environmental Research, Office of Science. Use of the Electron Microscopy Center at Argonne and the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at Argonne was performed under Contract DE-AC02-06CH11357. This work, including the efforts of Yiran Dong, Robert A. Sanford, Randall A. Locke, Jr., and Bruce W. Fouke, was funded by U.S. Department of Energy (DOE) (DE-FC26-05NT42588). Parts of this work, including the efforts of Yiran Dong, Robert A. Sanford, Janet Y. Chang, and Bruce Fouke, was also funded by National Aeronautics and Space Administration (NASA) (NNA13AA91A).


Photo micrograph of Orenia metallireducens strain Z6. Inset focus shows peritrichous pili produced by the organism. This bacterium was isolated from groundwater sampled from 2 kilometers deep within the Illinois Basin and is capable of reducing crystalline forms of ferric iron such as goethite and hematite. 

Source: This image was taken by the first author (Dr. Yiran Dong of the University of Illinois at Urbana-Champaign). It has not been used in a journal. She has given written permission for it to be used in the highlights database and other BER purposes. 

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