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  • 1
    ISSN: 1432-072X
    Keywords: Desulfotomaculum orientis ; Continuous culture ; Energetics of sulfate reduction ; Activation of sulfate ; Hydrogen ; Autotrophic growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Desulfotomaculum orientis (strain Singapore 1) was grown autotrophically with H2+CO2 and sulfate, thiosulfate or sulfite as electron acceptor in sulfide- and pH-controlled continuous culture. Under sulfate-limiting conditions real growth yields of up to 9.7 g cell dry mass per mol sulfate were obtained. Electron acceptor limitation resulted in the excretion of up to 14.5 mmol acetate per liter, formed by reduction of CO2 with H2. Acetate production was not coupled to an increase of growth yields: under hydrogen-limiting conditions only 1.6 mmol acetate per liter was produced, and even higher growth yields of up to 12,4 g cell dry mass per mol sulfate were obtained. With thiosulfate or sulfite as electron acceptor growth yields increased up to 17.9 g cell dry mass per mol electron acceptor. Growth yields were not simply correlated with the growth rate, and did not allow the determination of maintenance coefficients and the extrapolation to maximal yields at infinite growth rate (Y max). The maximal growth rates (μmax) with sulfate and thiosulfate were 0.090 and 0.109 h-1, respectively, if cells were grown continuously in sulfidostat culture under nonlimiting conditions. The net energy yield of sulfate reduction and the energy requirement for the activation of sulfate by Desulfotomaculum orientis are discussed.
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  • 2
    ISSN: 1432-072X
    Keywords: Sulfate-reducing bacteria ; Dissimilatory reduction of nitrate and nitrite to ammonia ; Chemostat culture ; Nitrate reductase ; Nitrite reductase ; Desulfobulbus propionicus ; Desulfovibrio desulfuricans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two of nine sulfate reducing bacteria tested,Desulfobulbus propionicus andDesulfovibrio desulfuricans (strain Essex 6), were able to grow with nitrate as terminal electron acceptor, which was reduced to ammonia. Desulfovibrio desulfuricans was grown in chemostat culture with hydrogen plus limiting concentrations of nitrate, nitrite or sulfate as sole energy source. Growth yields up to 13.1, 8.8 or 9.7 g cell dry mass were obtained per mol nitrate, nitrite or sulfate reduced, respectively. The apparent half saturation constants (K s) were below the detection limits of 200, 3 or 100 μmol/l for nitrate, nitrite of sulfate, respectively. The maximum growth rates {ie63-1} raised from 0.124 h-1 with sulfate and 0.150 h-1 with nitrate to 0.193 h-1 with nitrite as electron acceptor. Regardless of the electron acceptor in the culture medium, cell extracts exhibited absorption maxima corresponding to cytochromec and desulfoviridin. Nitrate reductase was found to be inducible by nitrate or nitrite, whereas nitrite reductase was synthesized constitutively. The activities of nitrate and nitrite reductases with hydrogen as electron donor were 0.2 and 0.3 μmol/min·mg protein, respectively. If limiting amounts of hydrogen were added to culture bottles with nitrate as electron acceptor, part of the nitrate was only reduced to the level of nitrite. In media containing nitrate plus sulfate or nitrite plus sulfate, sulfate reduction was suppressed. The results demonstrate that the ammonification of nitrate or nitrite can function as sole energy conserving process in some sulfate-reducing bacteria.
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  • 3
    ISSN: 1432-072X
    Keywords: Desulfovibrio desulfuricans ; Dissimilatory sulfate reduction ; Proton-anion symport ; Sulfite ; Thiosulfate ; Sulfide electrode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract pH changes and sulfide production upon addition of sulfate, sulfite or thiosulfate to non-buffered H2-saturated cell suspensions of Desulfovibrio desulfuricans were studied by means of electrodes. The addition of these electron acceptors resulted in a rapid alkalinization of the suspension which was accompanied by sulfide production. At-2° C, alkalinization without immediate sulfide production could be obtained. After addition of 35S-labelled sulfate at-2° C, the label was found to be concentrated 7,500-fold in the cells, while 2 protons per sulfate molecule had disappeared from the outer bulk phase. Alkalinization and sulfide production from micromolar electron acceptor additions depended on the transmembraneous proton gradient (Δ pH), and were reversibly inhibited in alkaline solution (pH〉8.0) or by the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP). Protonophore-inhibited sulfide production from sulfite or thiosulfate could be restored if the cell membranes were permeabilized by the detergent cetyltrimethylammonium bromide (CTAB), or if downhill transport was made possible by the addition of electron acceptors at millimolar concentrations. Sulfate was not reduced under these conditions, presumably because the cells did not contain ATP for its activation. K+-and Na+-ionophores such as nigericin, valinomycin or monensin appeared to be of limited efficiency in D. desulfuricans. In most experiments, sulfate reduction was inhibited by the K+−H+ antiporter nigericin in the presence of K+, but not by the thiocyanate anion or the K+-transporter valinomycin. The results indicate that sulfate, sulfite and thiosulfate are taken up by proton-anion symport, presumably as undissociated acids with an electroneutral mechanism, driven by the transmembraneous pH gradient (Δ pH) or by a solute gradient. Kinetics of alkalinization and sulfide production in cells grown with different electron acceptors revealed that D. desulfuricans has different specific uptake systems for sulfate and thiosulfate, and obviously also for sulfite. It is proposed that the electron acceptor transport finally will not consume net energy during growth in buffered medium: The protons taken up during active electron acceptor transport leave the cell with the reduced end-product by simple passive diffusion of H2S.
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  • 4
    ISSN: 1432-072X
    Keywords: Dissimilatory sulfate reduction ; Electron transport-driven proton translocation ; Hydrogenase ; Desulfovibrio desulfuricans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Proton translocation by washed cells of the sulfate-reducing bacterium Desulfovibrio desulfuricans strain Essex 6 was studied by means of pH and sulfide electrodes. Reversible extrusion of protons could be induced either by addition of electron acceptors to cells incubated under hydrogen, or by addition of hydrogen to cells incubated in the presence of an appropriate electron acceptor. Proton translocation was increased in the presence of ionophores that dissipate the membrane potential (thiocyanate, methyl triphenylphosphonium cation, but not valinomycin) and was sensitive to the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP). Upon micromolar additions of H2, usually sulfide was formed in stoichiometric amounts, and extrapolated H+/H2 ratios were 1.8±0.5 with sulfate, 2.3±0.3 with sulfite and 0.5±0.1 with thiosulfate. In several experiments hydrogen pulses caused increased proton extrusion not associated with sulfide production. This was a hint that sulfite might be reduced via intermediates. In the absence of H2S formation, extrapolated H+/H2 ratios were 3.1±0.8 with sulfate, 3.4±1.1 with sulfite, 4.4±0.8 with thiosulfate and 6.3±1.2 with oxygen. Micromolar pulses of electron acceptors to cells incubated under H2 caused less proton translocation than H2 pulses in presence of excess of electron acceptor; extrapolated H+/H2 ratios were 1.3±0.4 with sulfite, 3.3±0.9 with nitrite and 4.2±0.5 with oxygen. No proton translocation was observed after micromolar pulses of sulfate, thiosulfate or nitrate to cells incubated under hydrogen in the presence of thiocyanate. Inhibition experiments with CO and CuCl2 revealed that the hydrogenase activity was localized in the intracellular space, and that no periplasmic hydrogenase was present. The results indicate that D. desulfuricans can generate a proton gradient by pumping protons across the cytoplasmic membrane.
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  • 5
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    Springer
    Archives of microbiology 152 (1989), S. 296-301 
    ISSN: 1432-072X
    Keywords: Desulfotomaculum ruminis ; D. acetoxidans ; D. nigrificans ; D. orientis ; Desulfovibrio vulgaris ; Sulfate activation ; ATP sulfurylase ; Pyrophosphatase ; Pyrophosphate:acetate kinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Enzyme activities conceivably involved in the activation of sulfate were studied with Desulfotomaculum ruminis, D. acetoxidans, D. nigrificans, D. orientis, and Desulfovibrio vulgaris. Cell lysates of these species revealed activities of at least 8 nkat/mg protein (i.e., 480 nmol per min and mg protein) of ATP sulfurylase, acetate kinase, phosphotransacetylase and adenylate kinase. ADP sulfurylase was not detected. Pyrophosphatase activity was high (73 to 97 nkat/mg protein) in Desulfotomaculum orientis and Desulfovibrio vulgaris. In these strains pyrophosphatase was activated by addition of a reductant (dithionite). In Desulfotomaculum ruminis, D. acetoxidans, and D. nigrificans, only low pyrophosphatase activity (2.5 to 6.3 nkat/mg protein) was measured, which was not reductant-activated. Some hints indicated a membrane association of the pyrophosphatase in D. ruminis, and possibly also in D. acetoxidans and D. nigrificans. Activities of a pyrophosphate-dependent acetate kinase (PPi:acetate kinase), a PPi:AMP kinase or a polyphosphate:AMP kinase were not detected or negligible. The results are not in favour of the assumption that pyrophosphate formed by ATP sulfurylase during sulfate activation might be utilized to form acetyl phosphate in Desulfotomaculum species. Contrary results of other authors were shown to be artefacts caused by chemical hydrolysis of acetyl phosphate in the molybdate-sulfuric acid reagent used for phosphate determination.
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  • 6
    ISSN: 1432-072X
    Keywords: Transmembrane proton gradient ; Desulfovibrio desulfuricans CSN ; 31P NMR ; Cytoplasmic pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The transmembrane proton gradient of the sulfate-reducing bacterium Desulfovibrio desulfuricans strain CSN has been determined by in vivo31P nuclear magnetic resonance (NMR) spectroscopy in the absence of dioxygen. At pH 7.0 in the medium (pHex) the intracellular pH (pHin) was 7.5. By lowering pHex to 5.9 pHin decreased to 7.1. At pHex greater than 7.7 the transmembrane proton gradient (ΔpH) was zero. The uncouplers 3,3′,4′,5-tetrachlorosalicylanilide (TCS) and carbonylcyanide-m-chlorophenylhydrazone (CCCP), or the permeant anion thiocyanate caused complete dissipation of ΔpH.
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  • 7
    ISSN: 1432-072X
    Keywords: Chlorobium vibrioforme ; Desulfuromonas acetoxidans ; Purple nonsulfur bacteria ; Sulfur cycle ; H2 Photoproduction ; Electron donor acetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The marine green sulfur bacterium Chlorobium vibrioforme strain 1930 produced H2 and elemental sulfur from sulfide or thiosulfate under N limitation in the light. H2 production depended on nitrogenase and occurred only in the absence of ammonia. Methionine sulfoximine, an inhibitor of glutamine synthetase, prevented the switch-off by ammonia. In defined syntrophic cocultures of the acetate-oxidizing, sulfur-reducing bacterium Desulfuromonas acetoxidans with green sulfur bacteria, H2 was produced from acetate via a light-driven sulfur cycle. The sulfur-reducing bacterium could not be replaced by sulfate-reducing bacteria in these experiments. In a coculture of the marine Chlorobium vibrioforme strain 1930 and the sulfur-reducing bacterium Desulfuromonas acetoxidans strain 5071, optimum long-term H2 production from acetate was obtained with molecular nitrogen as N source, at low light intensity (110 μmol · m-2 · s-1), in sulfide-reduced mineral medium (2 mM Na2S) at pH 6.8. Traces of sulfide (10 μM) were sufficient to keep the sulfur cycle running. The coculture formed no poly-β-hydroxyalkanoates (PHA), but 20%–40% polysaccharide per cell dry mass. Per mol acetate added, the coculture formed 3.1 mol of H2 (78% of the theoretical maximum). Only 8% of the reducing equivalents was incorporated into biomass. The maximum rate of H2 production was 1300 ml H2 per day and g cell dry mass.
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  • 8
    ISSN: 1432-072X
    Keywords: Protonmotive force ; Membrane potential ; pH gradient ; Sodium ion gradient ; Sulfate transport ; Sodium ; sulfate symport ; Na+/H+ antiport ; Proton-stimulated ATP synthase ; Marine sulfate-reducing bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The sodium ion gradient and the membrane potential were found to be the driving forces of sulfate accumulation in the marine sulfate reducer Desulfovibrio salexigens. The protonmotive force of −158 mV, determined by means of radiolabelled membrane-permeant probes, consisted of a membrane potential of −140 mV and a pH gradient (inside alkaline) of 0.3 at neutral pHout. The sodium ion gradient, as measured with silicone oil centrifugation and atomic absorption spectroscopy, was eightfold ([Na+]out/[Na+]in) at an external Na+ concentration of 320 mM. The resulting sodium ionmotive force was −194 mV and enabled D. salexigens to accumulate sulfate 20000-fold at low external sulfate concentrations (〈0.1 μM). Under these conditions high sulfate accumulation occurred electrogenically in symport with three sodium ions (assuming equilibrium with the sodium ion-motive force). With increasing external sulfate concentrations sulfate accumulation decreased sharply, and a second, low-accumulating system symported sulfate electroneutrally with two sodium ions. The sodium-ion gradient was built up by electrogenic Na+/H+ antiport. This was demonstrated by (i) measuring proton translocation upon sodium ion pulses, (ii) studying uptake of sodium salts in the presence or absence of the electrical membrane potential, and (iii) the inhibitory effect of the Na+/H+ antiport inhibitor propylbenzilylcholin-mustard HCl (PrBCM). With resting cells ATP synthesis was found after proton pulses (changing the pH by three units), but neither after pulses of 500 mM sodium ions, nor in the presence of the uncoupler tetrachorosalicylanilide (TCS). It is concluded that the energy metabolism of the marine strain D. salexigens is based primarily on the protonmotive force and a protontranslocating ATPase.
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  • 9
    ISSN: 1432-072X
    Keywords: Key words     Sulfite reductase ; Desulfoviridin ; Membranes ; Carbon monoxide ; Reconstitution ; Cytochrome c3 ; Hydrogenase ; Ion chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract      The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fraction. On SDS-PAGE, both mSiR and sS iR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO3 –→H2S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c 3 from D. desulfuricans. The specific activity of mSiR was 103 nmol H2 min–1 mg–1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to differentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented th at, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO3 –→H2S was achieved by a membrane-bound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.
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  • 10
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Cultures from three groups of phototrophic bacteria (green sulphur bacteria, purple non-sulphur bacteria and purple sulphur bacteria) were investigated in respect of the quantum requirement for H2 production (QH2). Rates of H2 formation were determined by means of a Clark-type H2 electrode with dense suspensions of whole cells and malate, acetate or sulphide as electron donor. At low light intensities (0–3 W·m−2 of monochromatic light) the minimum quantum requirement was 8.6 quanta per H2 with Chlorobium vibrioforme, 7.5 with Rhodospirillum rubrum, and 23.2 with Ectothiorhodospira shaposhnikovii. The physiological efficiency, defined as the measured QH2 compared to the theoretical value calculated from the energy requirement of the physiological processes involved, was 94%, 88%, or 28%, respectively. With increasing light intensities the quantum requirement also increased. Various hydrogenase inhibitors either inhibited both H2 uptake and production (Cu2+, NO), or affected neither of these activities (CO, C2H2, N2O, ethylenedinitrilotetraacetate). An uptake hydrogenase-deficient Hup−-mutant of R. rubrum had higher rates of net H2 production but a similar quantum requirement. The energetic efficiency of H2 production by various biological and artificial systems is discussed.
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