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  • Active transport  (1)
  • Competition  (1)
  • Demethoxylation  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Acetate as a source of reducing equivalents in the reductive dechlorination of 2,5-dichlorobenzoate (1991)
    Springer
    Archives of microbiology 156 (1991), S. 356-361 
    Details
    ISSN: 1432-072X
    Keywords: Acetate oxidation ; Reduction equivalents ; Dehalogenation ; Dechlorination ; Demethoxylation ; Desulfomonile tiedjei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Desulfomonile tiedjei is the key dechlorinating organism in a three-tiered bacterial consortium that grows on the methanogenic degradation of 3-chlorobenzoate. 2,5-Dichlorobenzoate, however, is only converted to 2-chlorobenzoate and is not a methanogenic substrate for the consortium. The dechlorinator uses hydrogen produced from benzoate by the benzoate degrading member of consortium as its source of reducing equivalents for the dechlorination reaction. Incubation of 3-chlorobenzoate grown consortium cells with 2,5-dichlorobenzoate resulted in the consumption of acetate concurrent with the formation of 2-chlorobenzoate indicating that acetate can serve as an alternative source of reducing equivalents for reductive dechlorination. This interpretation was confirmed by the finding that the formation of 14CO2 from 2-14C-labeled acetate was stoichiometric. The addition of hydrogen to 2,5-dichlorobenzoate metabolizing cells resulted in (i) an 2.7-fold increase in the rate of dechlorination, and (ii) a drop in the amount of label recovered as CO2+CH4 from methyl 14C-labeled acetate, indicating that hydrogen was the preferred source of reducing equivalents for reductive dechlorination. Benzoate, an indirect source of H2 in the consortium, also inhibited the oxidation of acetate, while glucose, methanol, and butyrate did not affect labeled gas production and therefore were not suitable electron donors. Concomittant to dechlorination of 2,5-dichlorobenzoate 3- and 4-methoxybenzoate were converted to 3- and 4-hydroxybenzoate respectively. These conversions stimulated the rate of dechlorination 2-fold. Demethylation of 4-methoxybenzoate stimulated, but demethylation of 3-methoxybenzoate inhibited the oxidation of benzoate during the dechlorination of 2,5-dichlorobenzoate, suggesting that these isomers are metabolized through different pathways. Experiments with benzoate, 3-chlorobenzoate and 2,5-dichlorobenzoate metabolizing cells amended with 14CO2 showed that actively dechlorinating cells catalyzed an exchange reaction between CO2 and acetate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248710
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Assimilatory nitrate uptake in Pseudomonas fluorescens studied using nitrogen-13 (1981)
    Springer
    Archives of microbiology 129 (1981), S. 135-140 
    Details
    ISSN: 1432-072X
    Keywords: Pseudomonas fluorescens ; Assimilatory nitrate reduction ; Nitrate reductase ; Nitrate uptake ; Active transport ; Nitrogen-13 ; Short-lived isotope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanism of nitrate uptake for assimilation in procaryotes is not known. We used the radioactive isotope, 13N as NO3 -, to study this process in a prevalent soil bacterium, Pseudomonas fluorescens. Cultures grown on ammonium sulfate or ammonium nitrate failed to take up labeled nitrate, indicating ammonium repressed synthesis of the assimilatory enzymes. Cultures grown on nitrite or under ammonium limitation had measurable nitrate reductase activity, indicating that the assimilatory enzymes need not be induced by nitrate. In cultures with an active nitrate reductase, the form of 13N internally was ammonium and amino acids; the amino acid labeling pattern indicated that 13NO3 - was assimilated via glutamine synthetase and glutamate synthase. Cultures grown on tungstate to inactivate the reductase concentrated NO3 - at least sixfold. Chlorate had no effect on nitrate transport or assimilation, nor on reduction in cell-free extracts. Ammonium inhibited nitrate uptake in cells with and without active nitrate reductases, but had no effect on cell-free nitrate reduction, indicating the site of inhibition was nitrate transport into the cytoplasm. Nitrate assimilation in cells grown on nitrate and nitrate uptake into cells grown with tungstate on nitrite both followed Michaelis-Menten kinetics with similar K mvalues, 7 μM. Both azide and cyanide inhibited nitrate assimilation. Our findings suggest that Pseudomonas fluorescens can take up nitrate via active transport and that nitrate assimilation is both inhibited and repressed by ammonium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455349
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  • 3
    Electronic Resource
    Electronic Resource
    Competition between sulfate-reducing and methanogenic bacteria for H2 under resting and growing conditions (1984)
    Springer
    Archives of microbiology 137 (1984), S. 26-32 
    Details
    ISSN: 1432-072X
    Keywords: Desulfovibrio ; Methanospirillum ; Methanobacterium ; Methanosarcina ; Hydrogen kinetics ; Competition ; Monod kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The basis for the outcome of competition between sulfidogens and methanogens for H2 was examined by comparing the kinetic parameters of representatives of each group separately and in co-culture. Michaelis-Menten parameters (V max and K m) for four methanogens and five sulfate-reducing bacteria were determined from H2-depletion data. Further, Monod growth parameters (μmax, K s, Y H2) for Desulfovibrio sp. G11 and Methanospirillum hungatei JF-1 were similarly estimated. H2 K m values for the methanogenic bacteria ranged from 2.5 μM (Methanospirillum PM1) to 13 μM for Methanosarcina barkeri MS; Methanospirillum hungatei JF-1 and Methanobacterium PM2 had intermediate H2 K m estimates of 5 μM. Average H2 K m estimates for the five sulfidogens was 1.2 μM. No consistent difference among the V max estimates for the above sulfidogens (mean=100 nmol H2 min-1 mg-1 protein) and methanogens (mean=110 nmol H2 min-1 mg-1 protein) was found. A two-term Michaelis-Menten equation accurately predicted the apparent H2 K m values and the fate of H2 by resting co-cultures of sulfate-reducers and methanogens. Half-saturation coefficients (K s) for H2-limited growth of Desulfovibrio sp. G11 (2–4 μM) and Methanospirillum JF-1 (6–7 μM) were comparable to H2 K m estimates obtained for these organisms. Maximum specific growth rates for Desulfovibrio sp. G11 (0.05 h-1) were similar to those of Methanospirillum JF-1 (0.05–0.06 h-1); whereas G11 had an average yield coefficient 4 x that of JF-1. Calculated μmax and V max/K m values for the methanogens and sulfidogens studied predict that the latter bacterial group will process more H2 whether these organisms are in a growing or resting state, when the H2 concentration is in the first-order region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425803
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    Paper (German National Licenses)
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