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B Schink

Publications and source records attributed to B Schink.

At least 37 records · Page 2Linked to original sources
PubMed1999

Chlorobium ferrooxidans sp. nov., a phototrophic green sulfur bacterium that oxidizes ferrous iron in coculture with a "Geospirillum" sp. strain.

A green phototrophic bacterium was enriched with ferrous iron as sole electron donor and was isolated in defined coculture with a spirilloid chemoheterotrophic bacterium. The coculture oxidized ferrous iron to ferric iron with stoichiometric formation of cell mass from carbon dioxide. Sulfide, thiosulfate, or elemental sulfur was not used as electron donor in the light. Hydrogen or acetate in the presence of ferrous iron increased the cell yield of the phototrophic partner, and hydrogen could also be used as sole electron source. Complexed ferric iron was slowly reduced to ferrous iron in the dark, with hydrogen as electron source. Similar to Chlorobium limicola, the phototrophic bacterium contained bacteriochlorophyll c and chlorobactene as photosynthetic pigments, and also resembled representatives of this species morphologically. On the basis of 16S rRNA sequence comparisons, this organism clusters with Chlorobium, Prosthecochloris, and Pelodictyon species within the green sulfur bacteria phylum. Since the phototrophic partner in the coculture KoFox is only moderately related to the other members of the cluster, it is proposed as a new species, Chlorobium ferrooxidans. The chemoheterotrophic partner bacterium, strain KoFum, was isolated in pure culture with fumarate as sole substrate. The strain was identified as a member of the epsilon-subclass of the Proteobacteria closely related to "Geospirillum arsenophilum" on the basis of physiological properties and 16S rRNA sequence comparison. The "Geospirillum" strain was present in the coculture only in low numbers. It fermented fumarate, aspartate, malate, or pyruvate to acetate, succinate, and carbon dioxide, and could reduce nitrate to dinitrogen gas. It was not involved in ferrous iron oxidation but possibly provided a thus far unidentified growth factor to the phototrophic partner.

Bacteria, Anaerobic↗
PubMed1999

Anaerobic degradation of m-cresol by Desulfobacterium cetonicum is initiated by formation of 3-hydroxybenzylsuccinate.

The anaerobic bacterium Desulfobacterium cetonicum oxidized m-cresol completely with sulfate as electron acceptor. During growth, 3-hydroxybenzylsuccinate (identified by gas chromatography/mass spectroscopy and by comparison of high-performance liquid chromatography retention time and UV spectrum with a chemically synthesized reference compound) accumulated in the medium. This finding indicates that the methyl group of m-cresol is activated by addition to fumarate as in the case of anaerobic toluene metabolism. In cell-free extracts of D. cetonicum, the formation of 3-hydroxybenzylsuccinate from m-cresol and fumarate was detected at an activity of 0.5 nmol min(-1) (mg protein)(-1). This reaction depended strictly on anoxic assay conditions. Treatment with air resulted in a complete loss of activity; however, some activity could be recovered after restoring anoxic conditions. The activity was slightly membrane-associated. 3-Hydroxybenzylsuccinate was degraded via CoA thioesterification and further oxidation to 3-hydroxybenzoyl-CoA as subsequent steps in the degradation pathway.

Anaerobiosis↗
PubMed1999

Acetylene hydratase of Pelobacter acetylenicus. Molecular and spectroscopic properties of the tungsten iron-sulfur enzyme.

Acetylene hydratase of Pelobacter acetylenicus is a tungsten iron-sulfur protein involved in the fermentation of acetylene to ethanol and acetate. Expression of the enzyme was increased 10-fold by feeding a 50-L batch culture continuously with 104 Pa acetylene at pH 6.8-7.0. Acetylene hydratase was purified to homogeneity by a three-step procedure in either the absence or presence of dioxygen. The enzyme was a monomer with a molecular mass of 73 kDa (SDS/PAGE) or 83 kDa (matrix-assisted laser-desorption ionization MS) and contained 0.5 +/- 0.1 W (inductively coupled plasma/MS) and 1.3 +/- 0.1 molybdopterin-guanine dinucleotide per mol. Selenium was absent. EPR spectra (enzyme as isolated, under air) showed a signal typical of a [3Fe-4S] cluster with gav = 2.01, at 10 K. In enzyme prepared under N2/H2, this signal was absent and reaction with dithionite led to a rhombic signal with gz = 2.048, gy = 1.939 and gx = 1.920 indicative of a low-potential ferredoxin-type [4Fe-4S] cluster. Upon oxidation with hexacyanoferrate(III), a new signal appeared with gx = 2.007, gy = 2.019 and gz = 2.048 (gav = 2.022), which disappeared after further oxidation. The signal was still visible at 150 K and was tentatively assigned to a W(V) center. The iron-sulfur center of acetylene hydratase (prepared under N2/H2) gave a midpoint redox potential of -410 +/- 20 mV in a spectrophotometric titration with dithionite. Enzyme activity depended on the redox potential of the solution, with 50% of maximum activity at -340 +/- 20 mV. The presence of a pterin-guanine dinucleotide cofactor differentiates acetylene hydratase from the aldehyde ferredoxin oxidoreductase-type enzymes which have a pterin mononucleotide cofactor.

Bacteria, Anaerobic↗
PubMed1999

13C/12C isotope fractionation of aromatic hydrocarbons during microbial degradation.

The influence of microbial degradation on the 13C/12C isotope composition of aromatic hydrocarbons is presented using toluene as a model compound. Four different toluene-degrading bacterial strains grown in batch culture with oxygen, nitrate, ferric iron or sulphate as electron acceptors were studied as representatives of different environmental redox conditions potentially prevailing in contaminated aquifers. The biological degradation induced isotope shifts in the residual, non-degraded toluene fraction and the kinetic isotope fractionation factors alphaC for toluene degradation by Pseudomonas putida (1.0026 +/- 0.00017), Thauera aromatica (1.0017 +/- 0.00015), Geobacter metallireducens (1.0018 +/- 0.00029) and the sulphate-reducing strain TRM1 (1.0017 +/- 0.00016) were in the same range for all four species, although they use at least two different degradation pathways. A similar 13C/12C isotope fractionation factor (alphaC = 1.0015 +/- 0.00015) was observed in situ in a non-sterile soil column in which toluene was degraded under sulphate-reducing conditions. No carbon isotope shifts resulting from soil-hydrocarbon interactions were observed in a non-degrading soil column control with aquifer material under the same conditions. The results imply that microbial degradation of toluene can produce a 13C/12C isotope fractionation in the residual hydrocarbon fraction under different environmental conditions.

Carbon Isotopes↗
PubMed1999

Anaerobic degradation of naphthalene by a pure culture of a novel type of marine sulphate-reducing bacterium.

Incubation of marine sediment in anoxic, sulphate-rich medium in the presence of naphthalene resulted in the enrichment of sulphate-reducing bacteria. Pure cultures with short, oval cells (1.3 by 1.3-1.9 microm) were isolated that grew with naphthalene as the only organic carbon source and electron donor for sulphate reduction to sulphide. One strain, NaphS2, was characterized. It affiliated with completely oxidizing sulphate-reducing bacteria of the delta-subclass of the Proteobacteria, as revealed by 16S rRNA sequence analysis. 2-Naphthoate, benzoate, pyruvate and acetate were used in addition to naphthalene. Quantification of substrate consumption, sulphide formation and formed cell mass revealed that naphthalene was completely oxidized with sulphate as the electron acceptor.

Anaerobiosis↗
PubMed1998

Membrane-bound proton-translocating pyrophosphatase of Syntrophus gentianae, a syntrophically benzoate-degrading fermenting bacterium.

Syntrophus gentianae is a strictly anaerobic bacterium which ferments benzoate to acetate, CO2 and H2 in the presence of hydrogen-utilizing partner bacteria. Benzoate is activated by a benzoyl CoA ligase enzyme which forms AMP and pyrophosphate as coproducts. Pyrophosphatase activity was found to be largely membrane bound. Pyrophosphate hydrolysis was associated with proton translocation across the cytoplasmic membrane. Proton translocation could be abolished by the protonophor carbonylcyanide p-chlorophenylhydrazone, and could also be coupled to ATP formation in membrane vesicle preparations. The ratio of ATP formation/pyrophosphate hydrolysis was 1:3. The reverse reaction, ATP-dependent pyrophosphate synthesis, was possible with the same coupling stoichiometry. Pyrophosphatase was 90% saturated at 1 mM pyrophosphate; pyrophosphate concentrations higher than 5 mM inhibited enzyme activity. Inhibition studies with ATP and EDTA indicated that MgPPi- was probably the physiological substrate. The optimum temperature was 35 degrees C. In the presence of Mg2+, the enzyme was remarkably heat stable, with 50% of its maximum activity after 10 min at 60 degrees C. Exogenously added pyrophosphate could not be used for energy conservation.

Adenosine Triphosphate↗
PubMed1998

Anaerobic and aerobic oxidation of ferrous iron at neutral pH by chemoheterotrophic nitrate-reducing bacteria.

Nine out of ten anaerobic enrichment cultures inoculated with sediment samples from various freshwater, brackish-water, and marine sediments exhibited ferrous iron oxidation in mineral media with nitrate and an organic cosubstrate at pH 7.2 and 30 degrees C. Anaerobic nitrate-dependent ferrous iron oxidation was a biological process. One strain isolated from brackish-water sediment (strain HidR2, a motile, nonsporeforming, gram-negative rod) was chosen for further investigation of ferrous iron oxidation in the presence of acetate as cosubstrate. Strain HidR2 oxidized between 0.7 and 4.9 mM ferrous iron aerobically and anaerobically at pH 7.2 and 30 degrees C in the presence of small amounts of acetate (between 0.2 and 1.1 mM). The strain gained energy for growth from anaerobic ferrous iron oxidation with nitrate, and the ratio of iron oxidized to acetate provided was constant at limiting acetate supply. The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread capacity among mesophilic denitrifying bacteria. Since nitrate-dependent iron oxidation closes the iron cycle within the anoxic zone of sediments and aerobic iron oxidation enhances the reoxidation of ferrous to ferric iron in the oxic zone, both processes increase the importance of iron as a transient electron carrier in the turnover of organic matter in natural sediments.

Aerobiosis↗
PubMed1998

Anaerobic degradation of alpha-resorcylate by Thauera aromatica strain AR-1 proceeds via oxidation and decarboxylation to hydroxyhydroquinone.

Anaerobic degradation of alpha-resorcylate (3,5-dihydroxybenzoate) was studied with the denitrifying strain AR-1, which was assigned to the described species Thauera aromatica. alpha-Resorcylate degradation does not proceed via the benzoyl-CoA, the resorcinol, or the phloroglucinol pathway. Instead, alpha-resorcylate is converted to hydroxyhydroquinone (1,2,4-trihydroxybenzene) by dehydrogenative oxidation and decarboxylation. Nitrate, K3[Fe(CN)6], dichlorophenol indophenol, and the NAD+ analogue 3-acetylpyridine adeninedinucleotide were suitable electron acceptors for the oxidation reaction; NAD+ did not function as an electron acceptor. The oxidation reaction was strongly accelerated by the additional presence of the redox carrier phenazine methosulfate, which could also be used as sole electron acceptor. Oxidation of alpha-resorcylate with molecular oxygen in cell suspensions or in cell-free extracts of alpha-resorcylate- and nitrate-grown cells was also detected although this bacterium did not grow with alpha-resorcylate under an air atmosphere. alpha-Resorcylate degradation to hydroxyhydroquinone proceeded in two steps. The alpha-resorcylate-oxidizing enzyme activity was membrane-associated and exhibited maximal activity at pH 8.0. The primary oxidation product was not hydroxyhydroquinone. Rather, formation of hydroxyhydroquinone by decarboxylation of the unknown intermediate in addition required the cytoplasmic fraction and needed lower pH values since hydroxyhydroquinone was not stable at alkaline pH.

Anaerobiosis↗
PubMed1998

Energy conservation in the decarboxylation of dicarboxylic acids by fermenting bacteria.

Decarboxylation of dicarboxylic acids (oxalate, malonate, succinate, glutarate, and malate) can serve as the sole energy source for the growth of fermenting bacteria. Since the free energy change of a decarboxylation reaction is small (around -20 kJ per mol) and equivalent to only approximately one-third of the energy required for ATP synthesis from ADP and phosphate under physiological conditions, the decarboxylation energy cannot be conserved by substrate-level phosphorylation. It is either converted (in malonate, succinate, and glutarate fermentation) by membrane-bound primary decarboxylase sodium ion pumps into an electrochemical gradient of sodium ions across the membrane; or, alternatively, an electrochemical proton gradient can be established by the combined action of a soluble decarboxylase with a dicarboxylate/monocarboxylate antiporter (in oxalate and malate fermentation). The thus generated electrochemical Na+ or H+ gradients are then exploited for ATP synthesis by Na+- or H+-coupled F1F0 ATP synthases. This new type of energy conservation has been termed decarboxylation phosphorylation and is responsible entirely for ATP synthesis in several anaerobic bacteria.

Adenosine Triphosphate↗
PubMed1998

The fermenting bacterium Malonomonas rubra is phylogenetically related to sulfur-reducing bacteria and contains a c-type cytochrome similar to those of sulfur and sulfate reducers.

Malonomonas rubra is a microaerotolerant fermenting bacterium which can maintain its energy metabolism for growth by decarboxylation of malonate to acetate. 16S rRNA sequence analysis revealed that M. rubra is closely related to the cluster of mesophilic sulfur-reducing bacteria within the delta subclass of the Proteobacteria, with the fermenting bacterium Pelobacter acidigallici and the sulfur reducers Desulfuromusa kysingii, D. bakii and D. succinoxidans as closest relatives. The cells contain high amounts (up to 12% of the total cell protein content) of a c-type cytochrome which is present mainly (> 60%) in the cytoplasm and to minor parts in the periplasm (> 20%) and associated with the membrane fraction (> 10%), independent of the growth substrate. This cytochrome is a tetraheme cytochrome of 13,700 Da molecular mass with a midpoint redox potential of -0.210 V.M. rubra does not reduce sulfur or ferric iron compounds. Since this cytochrome appears not to be involved in the energy metabolism it is concluded that it is a remnant of sulfur-reducing ancestors of this bacterium, without a conceivable physiological function in its present energy metabolism.

Cytochrome c Group↗
PubMed1998

Fermentative degradation of 3-hydroxybenzoate in pure culture by a novel strictly anaerobic bacterium, Sporotomaculum hydroxybenzoicum gen. nov., sp. nov.

A strictly anaerobic bacterium, strain BT, from termite hindgut homogenates, was isolated in pure culture and grew on 3-hydroxybenzoate as sole source of carbon and energy. No other substrate tested was degraded, sulfate, sulfite, thiosulfate, nitrate, ferric iron, oxygen or fumarate were not reduced, and no electron transfer to partner organisms was observed. 3-Hydroxybenzoate was fermented to butyrate, acetate and CO2. Benzoate was detected in the culture supernatant as an intermediate. The isolate was a slightly motile, endosporeforming Gram-positive rod; 16S rDNA sequence analysis revealed a high similarity to members of the genus Desulfotomaculum. The G + C content of the DNA was 48 mol%. Strain BT differs from the members of the genus Desulfotomaculum significantly due to its lack of dissimilatory sulfate reduction, and is therefore described as the type strain of a new genus and species. Sporotomaculum hydroxybenzoicum gen. nov., sp. nov.

Animals↗
PubMed1998

Azoarcus anaerobius sp. nov., a resorcinol-degrading, strictly anaerobic, denitrifying bacterium.

A strictly anaerobic, nitrate-reducing bacterium, strain LuFRes1, was isolated using resorcinol as sole source of carbon and energy. The strain reduced nitrate to dinitrogen gas and was not able to use oxygen as an alternative electron acceptor. Cells were catalase-negative but superoxide-dismutase-positive. Resorcinol was completely oxidized to CO2. 16S rRNA sequence analysis revealed a high similarity with sequences of Azoarcus evansii and Azoarcus tolulyticus. Strain LuFRes1T (= DSM 12081T) is described as a new species of the genus Azoarcus, Azoarcus anaerobius.

Base Sequence↗
PubMed1998

Humic acid reduction by propionibacterium freudenreichii and other fermenting bacteria

Iron-reducing bacteria have been reported to reduce humic acids and low-molecular-weight quinones with electrons from acetate or hydrogen oxidation. Due to the rapid chemical reaction of amorphous ferric iron with the reduced reaction products, humic acids and low-molecular-weight redox mediators may play an important role in biological iron reduction. Since many anaerobic bacteria that are not able to reduce amorphous ferric iron directly are known to transfer electrons to other external acceptors, such as ferricyanide, 2,6-anthraquinone disulfonate (AQDS), or molecular oxygen, we tested several physiologically different species of fermenting bacteria to determine their abilities to reduce humic acids. Propionibacterium freudenreichii, Lactococcus lactis, and Enterococcus cecorum all shifted their fermentation patterns towards more oxidized products when humic acids were present; P. freudenreichii even oxidized propionate to acetate under these conditions. When amorphous ferric iron was added to reoxidize the electron acceptor, humic acids were found to be equally effective when they were added in substoichiometric amounts. These findings indicate that in addition to iron-reducing bacteria, fermenting bacteria are also capable of channeling electrons from anaerobic oxidations via humic acids towards iron reduction. This information needs to be considered in future studies of electron flow in soils and sediments.

Journal Article↗
PubMed1998

Growth of geobacter sulfurreducens with acetate in syntrophic cooperation with hydrogen-oxidizing anaerobic partners

Pure cultures of Geobacter sulfurreducens and other Fe(III)-reducing bacteria accumulated hydrogen to partial pressures of 5 to 70 Pa with acetate, butyrate, benzoate, ethanol, lactate, or glucose as the electron donor if electron release to an acceptor was limiting. G. sulfurreducens coupled acetate oxidation with electron transfer to an anaerobic partner bacterium in the absence of ferric iron or other electron acceptors. Cocultures of G. sulfurreducens and Wolinella succinogenes with nitrate as the electron acceptor degraded acetate efficiently and grew with doubling times of 6 to 8 h. The hydrogen partial pressures in these acetate-degrading cocultures were considerably lower, in the range of 0.02 to 0.04 Pa. From these values and the concentrations of the other reactants, it was calculated that in this cooperation the free energy change available to G. sulfurreducens should be about -53 kJ per mol of acetate oxidized, assuming complete conversion of acetate to CO2 and H2. However, growth yields (18.5 g of dry mass per mol of acetate for the coculture, about 14 g for G. sulfurreducens) indicated considerably higher energy gains. These yield data, measurement of hydrogen production rates, and calculation of the diffusive hydrogen flux indicated that electron transfer in these cocultures may not proceed exclusively via interspecies hydrogen transfer but may also proceed through an alternative carrier system with higher redox potential, e.g., a c-type cytochrome that was found to be excreted by G. sulfurreducens into the culture fluid. Syntrophic acetate degradation was also possible with G. sulfurreducens and Desulfovibrio desulfuricans CSN but only with nitrate as electron acceptor. These cultures produced cell yields of 4.5 g of dry mass per mol of acetate, to which both partners contributed at about equal rates. These results demonstrate that some Fe(III)-reducing bacteria can oxidize organic compounds under Fe(III) limitation with the production of hydrogen, and they provide the first example of rapid acetate oxidation via interspecies electron transfer at moderate temperature.

Journal Article↗
PubMed1998

Evidence of two oxidative reaction steps initiating anaerobic degradation of resorcinol (1,3-dihydroxybenzene) by the denitrifying bacterium Azoarcus anaerobius.

The denitrifying bacterium Azoarcus anaerobius LuFRes1 grows anaerobically with resorcinol (1,3-dihydroxybenzene) as the sole source of carbon and energy. The anaerobic degradation of this compound was investigated in cell extracts. Resorcinol reductase, the key enzyme for resorcinol catabolism in fermenting bacteria, was not present in this organism. Instead, resorcinol was hydroxylated to hydroxyhydroquinone (HHQ; 1,2,4-trihydroxybenzene) with nitrate or K3Fe(CN)6 as the electron acceptor. HHQ was further oxidized with nitrate to 2-hydroxy-1,4-benzoquinone as identified by high-pressure liquid chromatography, UV/visible light spectroscopy, and mass spectroscopy. Average specific activities were 60 mU mg of protein-1 for resorcinol hydroxylation and 150 mU mg of protein-1 for HHQ dehydrogenation. Both activities were found nearly exclusively in the membrane fraction and were only barely detectable in extracts of cells grown with benzoate, indicating that both reactions were specific for resorcinol degradation. These findings suggest a new strategy of anaerobic degradation of aromatic compounds involving oxidative steps for destabilization of the aromatic ring, different from the reductive dearomatization mechanisms described so far.

Anaerobiosis↗
PubMed1998

A periplasmic and extracellular c-type cytochrome of Geobacter sulfurreducens acts as a ferric iron reductase and as an electron carrier to other acceptors or to partner bacteria.

An extracellular electron carrier excreted into the growth medium by cells of Geobacter sulfurreducens was identified as a c-type cytochrome. The cytochrome was found to be distributed in about equal amounts in the membrane fraction, the periplasmic space, and the surrounding medium during all phases of growth with acetate plus fumarate. It was isolated from periplasmic preparations and purified to homogeneity by cation-exchange chromatography, gel filtration, and hydrophobic interaction chromatography. The electrophoretically homogeneous cytochrome had a molecular mass of 9.57 +/- 0.02 kDa and exhibited in its reduced state absorption maxima at wavelengths of 552, 522, and 419 nm. The midpoint redox potential determined by redox titration was -0.167 V. With respect to molecular mass, redox properties, and molecular features, this cytochrome exhibited its highest similarity to the cytochromes c of Desulfovibrio salexigens and Desulfuromonas acetoxidans. The G. sulfurreducens cytochrome c reduced ferrihydrite (Fe(OH)3), Fe(III) nitrilotriacetic acid, Fe(III) citrate, and manganese dioxide at high rates. Elemental sulfur, anthraquinone disulfonate, and humic acids were reduced more slowly. G. sulfurreducens reduced the cytochrome with acetate as an electron donor and oxidized it with fumarate. Wolinella succinogenes was able to reduce externally provided cytochrome c of G. sulfurreducens with molecular hydrogen or formate as an electron donor and oxidized it with fumarate or nitrate as an electron acceptor. A coculture could be established in which G. sulfurreducens reduced the cytochrome with acetate, and the reduced cytochrome was reoxidized by W. succinogenes in the presence of nitrate. We conclude that this cytochrome can act as iron(III) reductase for electron transfer to insoluble iron hydroxides or to sulfur, manganese dioxide, or other oxidized compounds, and it can transfer electrons to partner bacteria.

Cytochrome c Group↗
PubMed1997

Acetylene degradation by new isolates of aerobic bacteria and comparison of acetylene hydratase enzymes.

Aerobic acetylene-degrading bacteria were isolated from soil samples. Two isolates were assigned to the species Rhodococcus opacus, two others to Rhodococcus ruber and Gordona sp. They were compared with known strains of aerobic acetylene-, cyanide-, or nitrile-utilizing bacteria. The acetylene hydratases of R opacus could be measured in cell-free extracts only in the presence of a strong reductant like titanium(III) citrate. Expression of these enzymes was molybdenum-dependent. Acetylene hydratases in cell-free extracts of R ruber and Gordona spp. did not require addition of reductants. No cross-reactivity could be found between cell-free extracts of any of these aerobic isolates and antibodies raised against the acetylene hydratase of the strictly anaerobic fermenting bacterium Pelobacter acetylenicus. These results show that acetylene hydratases are a biochemically heterogeneous group of enzymes.

Acetylene↗