Dissimilatory reduction

Lovley DR, EJP Phillips (1988) Novel mode of microbial energy metabolism organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. Appl Environ Microbiol 54 1472-1480. 

McEwan AG, IP Ridge, CA McDevitt, P Hugenholtz (2002) The DMSO reductase family of microbial molybdenum enzymes molecular properties and the role in the dissimilatory reduction of toxic elements. 

Sani RK, BM Peyton, WA Smith, WA Apekl, JN Petersen (2002) Dissimilatory reduction of Cr(VI), Fe(III), and U(VI) by Cellulomonas isolates. Appl Microbiol Biotechnol 60 192-199. 

Wildung RE, YA Gorby, KM Krupka, NJ Hess, SW LI, AE Plymale, JP McKinley, JK Fredrickson (2000) Effect of electron donor and solution chemistry on products of dissimilatory reduction of technetium by Shewanella putrefaciens. Appl Environ Microbiol 66 2451-2460. 

Organic Carbon Oxidation Microbially Coupled to Reduction of Fe(III)(hydr)oxide. More and more evidence is accumulating that bacteria can grow anaerobically by coupling organic carbon oxidation to the dissimilatory reduction of iron(III) oxides (Nealson, 1982 Arnold et al., 1986 Lovely and Philips, 1988 Nealson and Myers, 1990). 

Lovley, D. R and E. J. P. Phillips (1988), "Novel Mode of Microbial Energy Metabolism Organic Carbon Oxidation Coupled to Dissimilatory Reduction of Iron or Manganese", Applied and Environ. Microbiology 54/6, 1472-1480. 

Although the sediments in these systems accumulate Se over time, the small isotopic contrast suggests that dissimilatory reduction is not the dominant accumulation mechanism. If dissimilatory reduction of Se(VI) and/or Se(IV) to Se(0) by bacteria were the dominant mechanism, one would expect the accumulated Se(0) to be enriched in the lighter isotope. In the San Francisco Estuary case, this assumes that the isotopic fractionations measured by Ellis et al. (2003) can be extrapolated to much lower concentrations. Incorporation of Se into algae and macrophyte tissues, followed by decay of some material and conversion of its Se to Se(0), is more consistent with the observed Se isotope data. Notably, the mean Se isotope composition of the Se(0) in the sediments of the Herbel et al. (2002) study was identical to that of the macrophytes. 

Herbel MJ, Johnson TM, Oremland RS, Bullen TD (1998) Selenium stable isotope fractionation during bacterial dissimilatory reduction of selenium oxyanions (Abstract). EOS, Transact. A.G.U. 79, Suppl. F356... 

Fredrickson JK, Zachara JM, Kennedy DW, Dong H, Onstott TC, Hinman NW, Li S (1998) Biogenic iron mineralization accompanying the dissimilatory reduction of hydrous ferric oxide by a groundwater bacterium. Geochim Cosmochim Acta 62 3239-3257... 

Lovley DR, Phillips EJP (1988) Novel mode of microbial energy metabolism organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. App Environ Microbio 54 1472-1480 Lovley DR, Stolz JF, Nord Jr GL, Phillips EJP (1987) Anaerobic production of magnetite by a dissimilatoiy iron-reducing microorganism. Nature 330 252-254... 

In many instances, substrate phosphorylation is not coupled to oxidation of the electron donor source by the bacteria therefore, growth will result from oxidative phosphorylation with electrons energizing the plasma membrane for ATP production according to the chemiosmotic system. A list of bacteria displaying dissimilatory reduction where growth is coupled to reduction of metaPmetalloid electron acceptors is given in Table 16.4. 

Several proteins were reported to function as enzymes for the dissimilatory reduction of metals and nonessential elements. As Usted in Table 16.4, the most frequently reported proteins involved in metal reduction are the cytochromes from sulfate-reducing bacteria. The focus on these cytochromes supports the initial papers by Lovley and colleagues in which they reported that reduced cytochrome Cs from Desulfovibrio vulgaris Hildenborough reduces uranyl salts (Lovley et al. 1993a) and chromate (Lovley and PhUhps 1994). 

Slobodkin AI, Jeanthon C, L Haridon S, et al. 1999a. Dissimilatory reduction of Fe(III) by thermophlic bacteria and archaea in deep subsurface petroleum reservoirs of western Siberia. Curr Microbiol 39 99-102. 

Dissimilatory Reductions under Suboxic and Anoxic Conditions... 

At this site in the eastern tropical North Pacific, denitrification is responsible fiar the midwater loss of nitrate and production of nitrite. The size of the secondary nitrite maximum is dependent on the relative rates of its production from NO3 and its loss via dissimilatory reduction to N2. The amount of nitrate lost to denitrification is shown as the difference between the measured nitrate and the calculated nitrate. The latter was estimated by multiplying the observed phosphate concentrations by the average nitrate-to-phosphate ratio in the three deepest samples (11.9 1.6pmolN/L). Note that the zone of denitrification is restricted to mid-depths, i.e., the depths of the OMZ at this site. 

Figure 4.1 shows that NOs" is the stable form of nitrogen over the usual range of pe + pH in aerobic environments. The fact that most of the N2 in the atmosphere has not been converted to NO3 therefore indicates that the biological mediation of this conversion in both directions is inefficient. Hence NO3 reduction to N2 occurs by indirect mechanisms involving intermediaries. Dissimilatory reduction of N03 (i.e. where the nitrogen oxide serves as an electron acceptor for the cell s metabolism but the N reduced is not used by the microbes involved) potentially occurs by two processes denitrification. 

As discussed in Chapter 5, in submerged soils nitrification occurs in aerobic sites at the iloodwater-soil and root-soil interfaces. Denitrification occurs upon diffusion of the NO, to the anaerobic bulk soil. Denitrification is favoured over dissimilatory reduction to NH4+(NO, -> NO2 NH4+) because of the large ratio of available carbon to electron acceptors in submerged soils. Denitrification is likely to proceed completely to N2 with little accumulation of N2O because of the very large sink and therefore steep concentration gradient of O2, and because carbon is less likely to be limiting (Section 5.1). 

Zobrist.J., Dowdle, R.S., Davis, J.A. Orem-land, R.S. (2000) Mobilization of arsenite by dissimilatory reduction of adsorbed arsenate. Envon. Sci. Technol. 34 4747-4753... 

Removal of sulfate from the water column can occur by either assimi-latory or dissimilatory reduction. Assimilatory reduction occurs in the water column, whereas uptake by plankton results in the formation of organic S. 

Dissimilatory reduction by anaerobic bacteria occurs in the anoxic hy-polimnion of stratified lakes and in sediments just below the oxic-anoxic boundary. It produces H2S,... 

Oremland, R.S., Dowdle, P.R., Hoeft, S. et al. (2000) Bacterial dissimilatory reduction of arsenate and sulfate in meromictic Mono Lake, California. Geochimica et Cosmochimica Acta, 64(18), 3073-84. 

Dissimilatory Reduction in Surficial Sediments. Porewater profiles from a number of sites throughout Little Rock Lake show that sulfate is always depleted below the sediment-water interface (Figure 3). Sulfate depletion in porewaters occurs not onlyin the soft gyttja but also in sandy, littoral sites with organic contents < 10%. The observed depletion of sulfate and the occurrence of H2S indicate that the sediments are anoxic immediately below the sediment-water interface and that sulfate reduction occurs in surficial sediments. 

Seston Sulfur. Much of the sulfur that is immobilized by assimilatoiy uptake or dissimilatory reduction is oxidized and reenters the water column as sulfate. We have approached the question of seston-S recycling by comparing carbon/sulfur (C/S) ratios in seston and sediment and by following the fate of 35S in labeled algae added to laboratory sediment-water microcosms. 

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