Geology topics

Elizabeth J.P. Phillips

Publications and source records attributed to Elizabeth J.P. Phillips.

25 records · Page 2Linked to original sources

USGS1990

Fe(III)-reducing bacteria in deeply buried sediments of the Atlantic Coastal Plain

The possibility that microorganisms are catalyzing the ongoing reduction of Fe(III) in the sediments of deep (20-250 m) aquifers was investigated. Acetate-oxidizing, Fe(III)-reducing bacteria were recovered from deep subsurface sediments, but only from sediments in which it appeared that Fe(III) reduction was the terminal electron-accepting process for oxidation of organic matter. The Fe(III)-reducing microorganisms were capable of reducing ferric oxides present in deep subsurface sediments. Although Fe(III) reduction in subsurface sediments is frequently regarded as an abiological reaction, the enzymatic reduction of Fe(III) by microorganisms reported here is the first mechanism of any kind actually shown to have the potential to couple the oxidation of organic matter to carbon dioxide with the reduction of Fe(III) under the environmental conditions typically found in deep aquifers. We propose that microbially catalyzed Fe(III) reduction is responsible for such late postdepositional phenomena as the formation of variegated red beds and the release of high concentrations of dissolved iron into anaerobic ground waters.

Geology↗

USGS1989

Oxidation of aromatic contaminants coupled to microbial iron reduction

THE contamination of sub-surface water supplies with aromatic compounds is a significant environmental concern1,2. As these contaminated sub-surface environments are generally anaerobic, the microbial oxidation of aromatic compounds coupled to nitrate reduction, sulphate reduction and methane production has been studied intensively1-7. In addition, geochemical evidence suggests that Fe(III) can be an important electron acceptor for the oxidation of aromatic compounds in anaerobic groundwater. Until now, only abiological mechanisms for the oxidation of aromatic compounds with Fe(III) have been reported8-12. Here we show that in aquatic sediments, microbial activity is necessary for the oxidation of model aromatic compounds coupled to Fe(III) reduction. Furthermore, a pure culture of the Fe(III)-reducing bacterium GS-15 can obtain energy for growth by oxidizing benzoate, toluene, phenol or p-cresol with Fe(III) as the sole electron acceptor. These results extend the known physiological capabilities of Fe(III)-reducing organisms and provide the first example of an organism of any type which can oxidize an aromatic hydrocarbon anaerobically.

Nature↗

USGS1989

Requirement for a microbial consortium to completely oxidize glucose in Fe(III)- reducing sediments

In various sediments in which Fe(III) reduction was the terminal electron-accepting process, [ 14 C]glucose was fermented to 14 C-fatty acids in a manner similar to that observed in methanogenic sediments. These results are consistent with the hypothesis that, in Fe(III)-reducing sediments, fermentable substrates are oxidized to carbon dioxide by the combined activity of fermentative bacteria and fatty acid-oxidizing, Fe(III)-reducing bacteria.

Maryland, Minnesota↗

USGS1989

Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens

The ability of Alteromonas putrefaciens to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory Fe(III) or Mn(IV) reduction was investigated. A. putrefaciens grew with hydrogen, formate, lactate, or pyruvate as the sole electron donor and Fe(III) as the sole electron acceptor. Lactate and pyruvate were oxidized to acetate, which was not metabolized further. With Fe(III) as the electron acceptor, A. putrefaciens had a high affinity for hydrogen and formate and metabolized hydrogen at partial pressures that were 25-fold lower than those of hydrogen that can be metabolized by pure cultures of sulfate reducers or methanogens. The electron donors for Fe(III) reduction also supported Mn(IV) reduction. The electron donors for Fe(III) and Mn(IV) reduction and the inability of A. putrefaciens to completely oxidize multicarbon substrates to carbon dioxide distinguish A. putrefaciens from GS-15, the only other organism that is known to obtain energy for growth by coupling the oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). The ability of A. putrefaciens to reduce large quantities of Fe(III) and to grow in a defined medium distinguishes it from a Pseudomonas sp., which is the only other known hydrogen-oxidizing, Fe(III)-reducing microorganism. Furthermore, A. putrefaciens is the first organism that is known to grow with hydrogen as the electron donor and Mn(IV) as the electron acceptor and is the first organism that is known to couple the oxidation of formate to the reduction of Fe(III) or Mn(IV). Thus, A. putrefaciens provides a much needed microbial model for key reactions in the oxidation of sediment organic matter coupled to Fe(III) and Mn(IV) reduction.

Applied and Environmental Microbiology↗

USGS1988

Manganese inhibition of microbial iron reduction in anaerobic sediments

Potential mechanisms for the lack of Fe(II) accumulation in Mn(IV)‐con‐taining anaerobic sediments were investigated. The addition of Mn(IV) to sediments in which Fe(III) reduction was the terminal electron‐accepting process removed all the pore‐water Fe(II), completely inhibited net Fe(III) reduction, and stimulated Mn(IV) reduction. In a solution buffered at pH 7, Mn(IV) oxidized Fe(II) to amorphic Fe(III) oxide. Mn(IV) naturally present in oxic freshwater sediments also rapidly oxidized Fe(II). A pure culture of a dissimilatory FE(III)‐ and Mn(FV)‐reducing organism isolated from the sediments reduced Fe(III) to Fe(II) in the presence of Mn(IV) when ferrozine was present to trap Fe(II) before Mn(IV) oxidized it. Depth profiles of dissolved iron and manganese reported in previous studies suggest that Fe(II) diffusing up from the zone of Fe(III) reduction is consumed within the Mn(IV)‐reducing zone. These results demonstrate that preferential reduction of Mn(IV) by Fe(III)‐reducing bacteria cannot completely explain the lack of Fe(II) accumulation in anaerobic, Mn(IV)‐containing sedments, and indicate that Mn(IV) oxidation of Fe(II) is the mechanism that ultimately prevents Fe(II) accumulation.

Geomicrobiology Journal↗

USGS1987

Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism

The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism 1 . The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments 2–4 . However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen 5 . We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and could account for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits.

Nature↗

USGS1987

Determination of Fe(III) and Fe(II) in oxalate extracts of sediment

A method was developed to determine the concentrations of oxalate-extractable Fe(III) and Fe(II) in sediments. Sediment was extracted in acid ammonium oxalate under N 2 . Iron(II) in the extract was determined with ferrozine. Iron(III) in the extract was reduced with hydroxylamine-hydrochloride, and total Fe in the extract was determined with ferrozine. Oxalate-extractable Fe(III) was calculated as the difference between Fe(II) and total Fe in the extract. Iron(II) was not oxidized, and Fe(III) was not reduced during the extraction. For an accurate estimate of oxalate-extractable Fe(III), fresh samples had to be analyzed, because air-drying or freeze-drying the samples oxidized Fe(II) to oxalate-extractable Fe(III). With a minimal increase in analytical effort, the method yields far more information on Fe geochemistry than the standard aerobic oxalate extraction method.

Soil Science Society of America Journal↗