5 items with the tag “oxidation

  • Chemolithotrophic Microbial Oxidation of Insoluble Fe(II)-Bearing Minerals
    NAI 2009 University of Wisconsin Annual Report

    Ferrous iron (Fe(II)) can serve as an energy source for a wide variety of chemolithotrophic microorganisms (organisms that gain energy from metabolism of inorganic compounds). Thought to be one of the oldest forms of microbial metabolism on Earth, Fe(II) oxidation may also have played a role in past (and possibly, present) life on Mars, whose crust is rich in Fe(II)-bearing silicate minerals (e.g. ultramafic basalt rocks). The initial goal of this project is to determine whether an established chemolithoautotrophic Fe(II)-oxidizing, nitrate-reducing culture can grow by oxidation of Fe(II) in basalt glass. Preliminary experiments suggest that the culture is able to oxidize a significant portion of the Fe(II) content of fresh basalt glass from Kilauea, a shield volcano in Hawaii that represents an analog for ancient volcanic activity on Mars.

    ROADMAP OBJECTIVES: 4.1 6.1 7.1
  • Project 2A: Chemolithotrophic Microbial Oxidation of Basalt Glass
    NAI 2010 University of Wisconsin Annual Report

    Ferrous iron (Fe(II)) can serve as an energy source for a wide variety of chemolithotrophic microorganisms (organisms that gain energy from metabolism of inorganic compounds). Fe(II) oxidation may have played a role in past (and possibly, present) life on Mars, whose crust is rich in Fe(II)-bearing silicate minerals (e.g. ultramafic basalt rocks). The goal of this project is to determine whether an established chemolithoautotrophic Fe(II)-oxidizing, nitrate-reducing culture can grow by oxidation of Fe(II) in basalt glass. Experiments showed that the culture is able to oxidize a significant portion (approximately 1%) of the Fe(II) content of fresh basalt glass from Kilauea, a shield volcano in Hawaii that represents an analog for ancient volcanic activity on Mars. The ratio of Fe(II) oxidized to nitrate reduced was consistent with the expected 1:5 stoichiometry, suggesting that the culture oxidized Fe(II) with nitrate in a manner analogous to its metabolism of other (e.g. aqueous) Fe(II) forms.

    ROADMAP OBJECTIVES: 2.1 6.2 7.1
  • Project 4A: Characterization of Novel Solid-Phase Fe(II)-Oxidizing Chemolithotrophic Bacteria From Subsurface Environments
    NAI 2011 University of Wisconsin Annual Report

    Ferrous iron (Fe(II)) can serve as an energy source for a wide variety of chemolithotrophic microorganisms (organisms that gain energy from metabolism of inorganic compounds). Fe(II) oxidation may have played a role in past (and possibly, present) life on Mars, whose crust is rich in primary Fe(II)-bearing silicate minerals, as well as Fe-bearing clay minerals formed during weathering of primary silicates. This project examined the physiological and phylogenetic properties of novel solid-phase Fe(II)-oxidizing bacteria (FeOB) isolated from subsurface sediments from the Columbia River basin in eastern Washington, as well as clay-rich subsoils from Madison, WI. The organisms were enriched using biotite (a Fe(II)-bearing primary silicate mineral) as an energy source, and purified on organics-containing medium. The capacity of the isolates to oxidize soluble and solid-phase Fe(II) compounds was assessed, and the 16S rRNA gene sequence for each of the isolate was determined. The results revealed that a wide variety of Proteobacteria are capable of catalyzing solid-phase Fe(II) oxidation, including several groups of organisms not previously known as FeOB. These results confirm and expand our knowledge of solid-phase chemolithotrophic Fe(II) oxidation on Earth, and bolster the concept of mineral-associated Fe(II) oxidation as a potential basis for microbial life on other terrestrial planets.

    ROADMAP OBJECTIVES: 3.2 5.1
  • Project 4E: Preliminary Studies of Fe Isotope Biogeochemistry in Fe-Rich Yellowstone National Park Hot Springs
    NAI 2012 University of Wisconsin Annual Report

    This preliminary project provided background information for future studies of the structure, function, and signatures (living and non-living) of Fe redox-based microbial life in the volcanic terrain of Yellowstone National Park (YNP). The focus on Fe redox-based systems stems from our expanding knowledge of the wide range of microbial energy metabolisms that are known to be associated with Fe redox transformations on Earth and potentially on other planets. Moreover, Fe redox transformations provide the potential for generation of mineralogical, isotopic, and organic biosignatures of past and present microbial life, which represent premier targets for testing the hypothesis that life currently exists or existed in the past on Mars. Preliminary data on Fe geochemistry and isotopic composition, and microbial community composition, was obtained for two contrasting Fe-rich springs in YNP: Chocolate Pots (CP), a warm, circumneutral environment that has formed on top of the Pleistocene-age Lava Creek Tuff, where a mixture of Fe-rich acid-sulfate geothermal fluids and neutral-pH groundwater from the Gibbon River catchment emerge to the surface; and The Gap site, a hot, acid-sulfate spring in the Norris Basin which supports active chemolithotrophic Fe(II) oxidation, analogous to other hot spring environments in YNP. The geochemical data demonstrated significant changes in aqueous Fe abundance and/or speciation along the flow paths at both sites, leading to accumulation of abundant Fe(III) oxides as well as aqueous Fe(III) at the acidic Gap site. A distinct separation in Fe isotope composition between aqueous Fe and deposited Fe(III) oxides (mainly amorphous Fe-Si coprecipitates) was also detected, with the oxide enriched in 56Fe relative to 54Fe as expected for redox-driven Fe isotope fractionation. However, the degree of fractionation was less the value of ca. 3 ‰ expected in closed system at isotope equilibrium. We suggest that internal regeneration of Fe(II) via dissimilatory Fe(III) reduction could enrich the aqueous Fe(II) pool in the heavy isotope, leading a much lower degree of Fe isotope fractionation – and hence a fundamentally different pattern of Fe isotope fractionation – than would occur in a strictly Fe(II) oxidation-driven reaction system. In support of this argument, an initial set of culturing experiments designed to recovery thermophilic Fe(III)-reducing organisms from CP and Gap materials resulted in the recovery of active Fe(III) reducers from both sites. In addition, preliminary pyrosequencing of 16S rRNA genes recovered from Gap solids provide evidence for Fe(III) reduction potential by the resident microflora. Particularly in the case of the Gap, sequences related to known Archaeal fermenters and elemental S/Fe(III) oxide reducers were abundant.

    ROADMAP OBJECTIVES: 2.1 5.1 5.3
  • Project 2F: Potential for Lithotrophic Microbial Oxidation of Fe(II) in Basalt Glass
    NAI 2012 University of Wisconsin Annual Report

    Ferrous iron (Fe(II)) can serve as an energy source for a wide variety of chemolithotrophic microorganisms (organisms that gain energy from metabolism of inorganic compounds). Fe(II) oxidation may have played a role in past (and possibly, present) life on Mars, whose crust is rich in primary Fe(II)-bearing silicate minerals, as well as Fe-bearing clay minerals formed during weathering of primary silicates. This project examined the potential for microbial oxidation of Fe(II) in basaltic glass. Recent research suggests that near‐surface hydrothermal venting may have occurred during past periods of active volcanic/tectonic activity on Mars. Such activities could have produced basalt glass phases that might have served as energy sources for chemolithotrophic microbial activity. Previous and ongoing NAI‐supported studies have shown that an established chemolithoautotrophic Fe(II)‐oxidizing, nitrate‐reducing culture can grow by oxidation of Fe(II) insoluble Fe(II)‐bearing phyllosilicate phases such as biotite and smectite. The initial goal of this project was to determine whether or not this culture is capable of oxidizing Fe(II) in basalt glass. In addition we tested basaltic glass oxidation by a culture of Desulfitobacterium frappieri, as previous studies demonstrated that D. frappieri is capable of nitrate-dependent oxidation of structural Fe(II) in smectite. Finally, in situ and enrichment culturing experiments were conducted to determine whether indigenous Fe(II)-oxidizing organisms in a groundwater iron seep were capable of colonization and oxidation of basaltic glass. The results of these experiments showed that while the various cultures were readily capable of smectite oxidation with nitrate, none were able to carry-out significant oxidation of Fe(II) in basalt glass. We speculate that Fe(II) atoms in the amorphous glass are somehow occluded and therefore not accessible to outer membrane cytochrome systems thought to be involved in extracellular Fe(II) oxidation.

    ROADMAP OBJECTIVES: 2.1 5.1 5.3