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 current 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 current knowledge of the metabolic diversity of bacteria that inhabit the subsurface. Previously thought to be largely sterile, researchers now know that microbial life dwells deep within the fractures and pore spaces of rocks that make up 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 iron minerals in 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, researchers isolated a novel member of the phylum Firmicutes, named Orenia metallireducens strain Z6. They found O. metallireducens to have numerous 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. The researchers also found that O. metallireducens is the only member of the order Halanaerobiales capable of reducing crystalline iron minerals such as goethite and hematite. This study’s results significantly expand the scope of phylogenetic affiliations, metabolic capabilities, and catalytic mechanisms that are known for iron-reducing microorganisms.

Principal Investigator

Kenneth Kemner
Argonne National Laboratory
kemner@anl.gov

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
paul.bayer@science.doe.gov

Funding

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

Related Links

• Subsurface Science Scientific Focus Area at Argonne National Laboratory

References