Concomitant Reduction Of Sulfate Research Articles

Sabkha and Burrow-Mediated Dolomitization in the Mississippian Debolt Formation, Northwestern Alberta, Canada

Dolomitized burrows in the Mississippian (Visean) Debolt Formation of northwestern Alberta, Canada form the primary reservoir intervals in the Dunvegan gas field. Sedimentological and ichnological analyses suggest a carbonate ramp setting that includes subenvironments such as sabkhas, hypersaline lagoons, restricted subtidal lagoons, intertidal mud flats, and peloidal shoals. Dolomitization occurs primarily within oxidized muds and highly bioturbated sediments, with the primary mode being sabkha-associated precipitation. In this context, dolomitization within the burrows also appears to be mediated by sulfate-reducing bacteria. δ18O values for dolomite within burrows (mean 2.4‰) are enriched by 1.3‰ relative to calcite values (mean 1.1‰) within the burrows. This degree of fractionation is similar for dolomite and calcite that have precipitated from the same solution. It is therefore suggested that the protodolomite precipitated in equilibrium with calcite rather than by replacement of pre-existing calcite. Isotopic values of δ13C measured for dolomite associated with burrows (mean 3.4‰) and matrix (mean 3.5‰) is slightly enriched relative to measured calcite values (mean 3.2‰ for matrix; mean 3.1‰ for burrows). These isotopic trends are common for modern dolomite that has precipitated in equilibrium with seawater where concomitant sulfate reduction and organic carbon-oxidation is inferred to occur near the surface.

Reduction of uranium(VI) under sulfate-reducing conditions in the presence of Fe(III)-(hydr)oxides

Hexavalent uranium [U(VI)] dissolved in a modified lactate-C medium was treated under anoxic conditions with a mixture of an Fe(III)-(hydr)oxide mineral (hematite, goethite, or ferrihydrite) and quartz. The mass of Fe(III)-(hydr)oxide mineral was varied to give equivalent Fe(III)-mineral surface areas. After equilibration, the U(VI)-mineral suspensions were inoculated with sulfate-reducing bacteria, Desulfovibrio desulfuricans G20. Inoculation of the suspensions containing sulfate-limited medium yielded significant G20 growth, along with concomitant reduction of sulfate and U(VI) from solution. With lactate-limited medium, however, some of the uranium that had been removed from solution was resolubilized in the hematite treatments and, to a lesser extent, in the goethite treatments, once the lactate was depleted. No resolubilization was observed in the lactate-limited ferrihydrite treatment even after a prolonged incubation of 4 months. Uranium resolubilization was attributed to reoxidation of the uraninite by Fe(III) present in the (hydr)oxide phases. Analysis by U L 3 -edge XANES spectroscopy of mineral specimens sampled at the end of the experiments yielded spectra similar to that of uraninite, but having distinct features, notably a much more intense and slightly broader white line consistent with precipitation of nanometer-sized particles. The XANES spectra thus provided strong evidence for SRB-promoted removal of U(VI) from solution by reductive precipitation of uraninite. Consequently, our results suggest that SRB mediate reduction of soluble U(VI) to an insoluble U(IV) oxide, so long as a suitable electron donor is available. Depletion of the electron donor may result in partial reoxidation of the U(IV) to soluble U(VI) species when the surfaces of crystalline Fe(III)-(hydr)oxides are incompletely reduced.

A Syntrophic Propionate-Oxidizing, Sulfate-Reducing Bacterium from a Fluidized Bed Reactor

Summary A mixed-culture HP1 was enriched with propionate/sulfate from a methanogenic fluidized bed reactor fed with propionate as the sole organic carbon source in a medium low in sulfate. The mixed-culture contained strain HP 1.1 as the only propionate-oxidizer, which was Gram-negative, lemon- or peanut-shaped, 0.95-1.15 x 1.4-2.4 µm in size, occurred singly or in pairs, and did not form endospores. Strain HP1.1 oxidized propionate to acetate and carbon dioxide with concomitant reduction of sulfate. Scanning electron microscopy revealed that strain HP1.1 was morphologically distinct from Syntrophobacter wolinii and Desulfobulbus propionicus. We separated strain HP1.1 from other strains by Percoll gradient centrifugation, and from these cells the total sequence of 16S rDNA from the PCR-amplified 16S rRNAgene from DNA was obtained. The phylogenetic analysis revealed that strain HP1.1 was less closely related to Syntrophobacter wolinii than to two recently described, propionate-oxidizing strains MPOB and KoPropl within the 8-subclass of the Proteobacteria (Ddrner, 1992; Harmsen et al., 1995), while a more distant relationship was found to Desulfobulbus propionicus.

Anaerobic oxidation of saturated hydrocarbons to CO2 by a new type of sulfate-reducing bacterium

n-Hexadecane added as electron donor and carbon source to an anaerobic enrichment culture from an oil production plant or to anoxic marine sediment samples allowed dissimilatory sulfate reduction to sulfide. The enrichment from the oil field was purified via serial dilutions in liquid medium under a hexadecane phase and in agar medium with caprylate. A pure culture of a sulfate-reducing bacterium, strain Hxd3, with relatively tiny cells (0.4–0.5 by 0.8–2 μm) was isolated that grew anaerobically on hexadecane without addition of further organic substrates. Most of the cells were found to adhere to the hydrocarbon phase. It was verified that neither organic impurities in hexadecane nor residual oxygen were responsible for growth. Strain Hxd3 was grown with n-hexadecane of high purity (≥99.5%) in anoxic glass ampoules sealed by fusion. Of 0.4 ml hexadecane added per l (1.4 mmol per l), 90% was degraded with concomitant reduction of sulfate. Controls with pasteurized cells or a common Desulfovibrio species neither consumed hexadecane nor reduced sulfate. Incubation of cell-free medium with low reducing capacity and a redox indicator showed that the ampoules were completely oxygen-tight. Measured degradation balances and enzyme activities suggested a complete oxidation of the alkane to CO2 via the carbon monoxide dehydrogenase pathway. However, the first step in anaerobic alkane oxidation is unknown. On hexadecane, strain Hxd3 produced as much as 15 to 20 mM H2S, but growth was rather slow; with 5% inoculum, cultures were fully grown after 5 to 7 weeks. The new sulfate reducer grew on alkanes from C12 to C20, 1-hexadecene, 1-hexadecanol, 2-hexadecanol, palmitate and stearate. Best growth occurred on stearate (doubling time around 26 h). Growth on soluble fatty acids such as caprylate was very poor. Alkanes with chains shorter than C12, lactate, ethanol or H2 were not used. Strain Hxd3 is the first anaerobe shown to grow definitely on saturated hydrocarbons.

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments.

Colony counts of acetate-, propionate- and L-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers. Anaerobic mineralization of acetate, propionate and L-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. L-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, L-lactate and ethanol were oxidized with concomitant sulfate reduction. L-Lactate and pyruvate could be fermented by most of the isolated strains.

Geologic Controls on Mineral-Matter Content of Coal in Central Appalachian Basin: ABSTRACT

Mineral-matter content of coal in the central Appalachian basin was primarily controlled by chemical conditions in a peat-forming paleoenvironment. Coal that is low in mineral matter was derived from peat that accumulated under highly acidic conditions (pH<4.5), whereas coal having high mineral-matter content was derived from peat that accumulated under pH conditions ranging from 4.5 to 7.5. Highly acid conditions during the peat-forming stage of coal formation favored leaching of mineral matter and inhibited bacterial degradation. Increasing pH resulting from buffering by dissolved calcium carbonate species could have (1) reduced the degree of leaching of mineral matter and (2) concentrated mineral matter, including sulfur compounds, because of increased bacterial deg adation of peat and concomitant sulfate reduction. Coal that has a low mineral-matter content (1) is associated with noncalcareous sedimentary sequences; (2) has a high kaolinite to illite ratio; and (3) has a relatively low calcium carbonate content. The converse is true for coal having high mineral-matter content. Mineral matter other than calcium, iron, and sulfur in Appalachian basin coal is dominated by inherent ash derived from plants. Calcium, iron, and sulfur contents are thought to have been fixed primarily by chemical reactions indirectly resulting from bacterial degradation during the early stages of coal formation. End_of_Article - Last_Page 689------------