Sulfates, reduction

Free sulfur is rarely present in crude oils, but it can be found in suspension or dissolved in the liquid. The crude from Goldsmith (Texas, USA.) is richest in free sulfur (1% by weight for a total sulfur content of 2.17%). It could be produced by compounds in the reservoir rock by sulfate reduction (reaction 8.2). 

In water containing sulfate, the use of the electrolysis protection process with low water consumption can sometimes result in the formation of small amounts of HjS, which is detectable by the smell. Sulfate reduction occurs through the action of bacteria in anaerobic areas (e.g., in the slurry zone of the tank). 

On the other hand, electrochemical sulfate reduction has not been confirmed... 

R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

Dissimilatory sulfate reduction (SO - - H2S) Sulfate-reducing bacteria... 

The case of bacterial reduction of sulfate to sulfide described by Berner (1984) provides a useful example. The dependence of sulfate reduction on sulfate concentration is shown in Fig. 5-4. Here we see that for [SO ] < 5 mM the rate is a linear function of sulfate concentration but for [SO4 ] > 10 itiM the rate is reasonably independent of sulfate concentration. The sulfate concentration in the ocean is about 28 mM and thus in shallow marine sediments the reduction rate does not depend on sulfate concentration. (The rate does depend on the concentration of organisms and the concentration of other necessary reactants - organic carbon in this case.) In freshwaters the sulfate concentration is... 

Fig. 5-4 The rate of bacterial sulfate reduction as a function of sulfate concentration. (Adapted from Berner (1984) with the permission of Pergamon Press.)...

Berner, R. A. (1972). Sulfate reduction, pyrite formation and the oceanic sulfur budget. In "The changing chemistry of the oceans" (D. Dyrssen and D. Jagner, eds). Wiley-Interscience, Stockholm. 

This key enzyme of the dissimilatory sulfate reduction was isolated from all Desulfovibrio strains studied until now 135), and from some sulfur oxidizing bacteria and thermophilic Archaea 136, 137). The enzymes isolated from sulfate-reducing bacteria contain two [4Fe-4S] clusters and a flavin group (FAD) as demonstrated by visible, EPR, and Mossbauer spectroscopies. With a total molecular mass ranging from 150 to 220 kDa, APS reductases have a subunit composition of the type 012)32 or 02)3. The subunit molecular mass is approximately 70 and 20 kDa for the a and )3 subunits, respectively. Amino-acid sequence data suggest that both iron-sulfur clusters are located in the (3 subunit... 

Sulfite reductase catalyzes the six-electron reduction of sulfite to sulfide, m essential enzymatic reaction in the dissimilatory sulfate reduction process. Several different types of dissimilatory sulfite reductases were already isolated from sulfate reducers, namely desul-foviridin (148-150), desulforubidin (151, 152), P-582 (153, 154), and desulfofuscidin (155). In addition to these four enzymes, an assimila-tory-type sulfite reductase was also isolated from D. vulgaris. Although all these enzymes have significantly different subunit composition and amino acid sequences, it is interesting to note that, as will be discussed later, all of them share a unique type of cofactor. 

Although the foregoing reactions involve dehalogenation by reduction or elimination, nucleophilic displacement of chloride may also be important. This has been examined with dihalomethanes using HS at concentrations that might be encountered in environments where active anaerobic sulfate reduction is taking place. The rates of reaction with HS exceeded those for hydrolysis and at pH values above 7 in systems that are in equilibrium with elementary sulfur, the rates with polysulfide exceeded those with HS. The principal product from dihalomethanes was the polythio-methylene HS (CH2-S) H (Roberts et al. 1992). 

The conditions under which these function and their regulation depend on the organism. For example, in Escherichia coli, oxygen represses the synthesis of the other reductases, and under anaerobic conditions the reductases for fumarate, DMSO, and TMAO are repressed by nitrate. This does not apply to Wolinella succinogenes in which sulfur represses the synthesis of the more positive electron acceptors nitrate and fumarate (Lorenzen et al. 1993). The DMSO reductase from Escherichia coli (Weiner et al. 1988) has a broad substrate versatility, and is able to reduce a range of sulfoxides and A-oxides. Anaerobic sulfate reduction is not discussed here in detail. 

Newman DK, EK Kennedy, JD Coates, D Ahmann, DJ Ellis, DR Lovley, EMM Morel (1997) Dissimilatory arsenate and sulfate reduction in Desulfotomaculum auripigmentum sp. nov. Arch Microbiol 168 ... 

Truly field experiments on microbial reactions are extremely difficult to carry out, but a series of microcosm experiments on the substrates that may support anaerobic sulfate reduction quite closely... 

There is evidence for the anaerobic degradation of alkanes to COj, plausibly under conditions of sulfate reduction. In experiments with sediment slurries from contaminated marine areas, was recovered from " C-hexadecane (Coates et al. 1997), and was inhibited by molybdate that is consistent with the involvement of sulfate reduction. Under sulfate-reducing conditions was produced from C[14,15]octacosane (CagHjg) (Caldwell et al. 1998). Different mechanisms have been elucidated for the anaerobic degradation of higher alkanes, and both occurred simultaneously in a sulfate-reducing consortium (Callaghan et al. 2006) ... 

Isotope fractionation during sulfate reduction by the hyperthermophilic Archaeoglobus fulgidus varied with the concentration of sulfate, and it was suggested that different pathways were operative at concentrations >0.6 or <0.3 mM (Habicht et al. 2005). 

Habicht KS, L Sailing, B Thamdrup, DE Canfield (2005) Effect of low sulfate concentrations on lactate oxidation and isotope fractionation during sulfate reduction by Archaeoglobus fulgidus strain Z. Appl Environ Microbiol 71 3110-3111. 

Woodruff, L.G. and Shanks, W.C. Ill (1988) Sulfur isotope. study of chimney minerals and vent fluids from 21°N East Pacific Rise Hydrothermal sulfur sources and disequilibrium sulfate reduction. J. Geophys. Res., 93, 4562-4572,... 

A sulfate-reducing bacterium was isolated by enrichment with a lactate-sulfate medium containing 3% NaCl. This isolate utilized lactate as an electron donor for sulfate reduction and contained desulfoviridin, typical of the genus Desulfovibrio [695]. 

G. G. Hoffmann and I. Steinfatt. Thermochemical sulfate reduction at steam flooding processes— chemical approach. In ACS Petrol Chem Div Preprints, volume 38, pages 181-184. 205th ACS Nat Mtg Enhanced Oil Recovery Symp (Denver, CO, 3/28-4/2), February 1993. 

Stein, O.R., Borden-Stewart, D.J., Hook, P.B., and Jones, W.L., Seasonal influence on sulfate reduction and zinc sequestration in subsurface treatment wetlands, Water Research, 41 (15), 3440-3448, 2007. 

Capone, D.G., Reese, D.D., and Kiene, R.P., Effects of metals on methanogenesis, sulfate reduction, carbon dioxide evolution, and microbial biomass in anoxic salt marsh sediments, Appl Environ Microbiol, 45 (5), 1586-1591, 1983. 

Aerobic respiration Denitrification Mn(IV) reduction Fe(III) reduction Sulfate reduction Methane fermentation Nitrogen fixation... 

Belle Glade Carbonate Hot acid Organic plant wastes Neutralization Bacterial sulfate reduction Methane production... 

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