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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 22 (1998), S. 0 
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The capacity of some bacteria to metabolize hydrocarbons in the absence of molecular oxygen was first recognized only about ten years ago. Since then, the number of hydrocarbon compounds shown to be catabolized anaerobically by pure bacterial cultures has been steadily increasing. This review summarises the current knowledge of the bacterial isolates capable of anaerobic mineralization of hydrocarbons, and of the biochemistry and molecular biology of enzymes involved in the catabolic pathways of some of these substrates. Several alkylbenzenes, alkanes or alkenes are anaerobically utilized as substrates by several species of denitrifying, ferric iron-reducing and sulfate-reducing bacteria. Another group of anaerobic hydrocarbon degrading bacteria are ‘proton reducers’ that depend on syntrophic associations with methanogens. For two alkylbenzenes, toluene and ethylbenzene, details of the biochemical pathways involved in anaerobic mineralization are known. These hydrocarbons are initially attacked by novel, formerly unknown reactions and oxidized further to benzoyl-CoA, a common intermediate in anaerobic catabolism of many aromatic compounds. Toluene degradation is initiated by an unusual addition reaction of the toluene methyl group to the double bond of fumarate to form benzylsuccinate. The enzyme catalyzing this first step has been characterized at both the biochemical and molecular level. It is a unique type of glycyl-radical enzyme, an enzyme family previously represented only by pyruvate-formate lyases and anaerobic ribonucleotide reductases. Based on the nature of benzylsuccinate synthase as a radical enzyme, a hypothetical reaction mechanism for the addition of toluene to fumarate is proposed. The further catabolism of benzylsuccinate to benzoyl-CoA and succinyl-CoA appears to occur via reactions of a modified β-oxidation pathway. Ethylbenzene is first oxidized at the methylene carbon to 1-phenylethanol and subsequently to acetophenone, which is then carboxylated to 3-oxophenylpropionate and converted to benzoyl-CoA and acetyl-CoA. Anaerobic mineralization of alkanes involves an oxygen-independent oxidation to fatty acids, followed by β-oxidation. In one strain of an alkane-mineralizing sulfate-reducing bacterium, the activation appears to proceed via a chain-elongation, possibly by addition of a C1-group at the terminal methyl group of the alkane. Finally, aspects concerned with the regulation and ecological significance of anaerobic hydrocarbon catabolic pathways are discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 31 (1985), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The survival after oxygen stress was studied with eight species of sulfate-reducing bacteria. In the absence of sulfide all species tolerated 6 min of aeration without loss of viability. Even after 3 h of aeration the viability of four species (Desulfovibrio vulgaris, D. desulfuricans, D. salexigens and Desulfobacter postgatei) was not impaired. Four other species were sensitive to 3 h of aeration: the surviving fractions of Desulfotomaculum ruminis, D. nigrificans and Desulfococcus multivorans were about 1%, that of Desulfotomaculum orientis about 0.01%. Formation of spores resulted in oxygen resistance of D. orientis. Reducing agents did not protect the vegetative cells of this strain against oxygen toxicity. In contrast, sulfhydryl group-containing agents increased the oxygen sensitivity considerably.Growth of sulfate- and sulfur-reducing bacteria in oxygen-sulfide gradients in agar tubes was studied. In the gradients these strictly anaerobic bacteria revealed oxygen-dependent growth in sulfate- and sulfur-free medium. Three sulfate-reducing bacteria that could not use thiosulfate or sulfur as electron acceptor failed to grow in oxygen-sulfide gradients. Obviously, not directly molecular oxygen, but oxidation products of sulfide, such as thiosulfate or sulfur, were used as electron acceptors and were continuously regenerated in a cycling process from sulfide by autoxidation. The conceivable ecological significance of a short sulfur cycle driven by autoxidation of sulfide is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 31 (1985), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Methanosarcina barkeri cells were observed in ammonia-free anaerobic acetate enrichments for sulfate-reducing bacteria. The capacity of Methanosarcina to grow diazotrophically was proved with a pure culture in mineral media with methanol. The cell yields with N2 or NH4+ ions as nitrogen source were 2.2 g and 6.1 g dry weight, respectively, per mol of methanol. Growth experiments with 15N2 revealed that 84% of the cell nitrogen was derived from N2. Acetylene was highly toxic to Methanosarcina and only reduced at concentrations lower than 100 μmol dissolved per 1 of medium. Assimilation of N2 and reduction of acetylene were inhibited by NH4+ ions. The experiments show that N2 fixation occurs not only in eubacteria but also in archaebacteria. The ecological significance of diazotrophic growth of Methanosarcina is discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 266-269 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Biological formation of methane is the terminal process of biomass degradation in aquatic habitats where oxygen, nitrate, ferric iron and sulphate have been depleted as electron acceptors. The pathway leading from dead biomass to methane through the metabolism of anaerobic bacteria and archaea ...
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 25 (1986), S. 169-174 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary In anaerobic corrosion experiments, hydrogenase-positiveDesulfovibrio strains, grown with limiting lactate concentrations in the presence of steel wool, formed more sulphide than expected or observed with lactate alone. The additional sulphide obviously originated from sulphate reduction with cathodically formed hydrogen from the steel surface. The hydrogenasenegativeD. sapovorans did not produce additional sulphide. The observations agree with the theory of von Wolzogen Kühr and van der Vlugt (1934) that explains anaerobic corrosion as a cathodic depolarization of iron surfaces by hydrogen-consuming sulphate-reducing bacteria. The influence of the iron surface area, the salt concentration and the pH-value on the utilization of cathodically formed hydrogen was investigated. The significance of an additional organic electron donor for the corrosion of iron in aqueous environments is discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 163 (1995), S. 96-103 
    ISSN: 1432-072X
    Keywords: Anaerobic degradation ; Aromatic hydrocarbons ; Alkylbenzenes ; Ethylbenzene ; Crude oil ; Denitrifying bacteria ; Phylogeny ; Thauera selenatis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Anaerobic degradation of alkylbenzenes with side chains longer than that of toluene was studied in freshwater mud samples in the presence of nitrate. Two new denitrifying strains, EbN1 and PbN1, were isolated on ethylbenzene and n-propylbenzene, respectively. For comparison, two further denitrifying strains, ToN1 and mXyN1, were isolated from the same mud with toluene and m-xylene, respectively. Sequencing of 16SrDNA revealed a close relationship of the new isolates to Thauera selenatis. The strains exhibited different specific capacities for degradation of alkylbenzenes. In addition to ethylbenzene, strain EbN1 utilized toluence, but not propylbenzene. In contrast, propylbenzene-degrading strain PbN1 did not grow on toluene, but was able to utilize ethylbenzene. Strain ToN1 used toluene as the only hydrocarbon substrate, whereas strain mXyN1 utilized both toluene and m-xylene. Measurement of the degradation balance demonstrated complete oxidation of ethylbenzene to CO2 by strain EbN1. Further characteristic substrates of strains EbN1 and PbN1 were 1-phenylethanol and acetophenone. In contrast to the other isolates, strain mXyN1 did not grow on benzyl alcohol. Benzyl alcohol (also m-methylbenzyl alcohol) was even a specific inhibitor of toluene and m-xylene utilization by strain mXyN1. None of the strains was able to grow on any of the alkylbenzenes with oxygen as electron acceptor. However, polar aromatic compounds such as benzoate were utilized under both oxic and anoxic conditions. All four isolates grew anaerobically on crude oil. Gas chromatographic analysis of crude oil after growth of strain ToN1 revealed specific depletion of toluene.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 152 (1989), S. 479-483 
    ISSN: 1432-072X
    Keywords: Methanogenic bacteria ; Alcohols ; Alcohol dehydrogenase ; Ethanol ; Acetaldehyde ; Acetate ; NADP ; Factor F420 ; Methanogenium organophilum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methanogenium organophilum, a non-autotrophic methanogen able to use primary and secondary alcohols as hydrogen donors, was grown on ethanol. Per mol of methane formed, 2 mol of ethanol were oxidized to acetate. In crude extract, an NADP+-dependent alcohol dehydrogenase (ADH) with a pH optimum of about 10.0 catalyzed a rapid (5 μmol/min·mg protein; 22°C) oxidation of ethanol to acetaldehyde; after prolonged incubation also acetate was detectable. With NAD+ only 2% of the activity was observed. F420 was not reduced. The crude extract also contained F420: NADP+ oxidoreductase (0.45 μmol/min·mg protein) that was not active at the pH optimum of ADH. With added acetaldehyde no net reduction of various electron acceptors was measured. However, the acetaldehyde was dismutated to ethanol and acetate by the crude extract. The dismutation was stimulated by NADP+. These findings suggested that not only the dehydrogenation of alcohol but also of aldehyde to acid was coupled to NADP+ reduction. If the reaction was started with acetaldehyde, formed NADPH probably reduced excess aldehyde immediately to ethanol and in this way gave rise to the observed dismutation. Acetate thiokinase activity (0.11 μmol/min·mg) but no acetate kinase or phosphotransacetylase activity was observed. It is concluded that during growth on ethanol further oxidation of acetaldehyde does not occur via acetylCoA and acetyl phosphate and hence is not associated with substrate level phosphorylation. The possibility exists that oxidation of both ethanol and acetaldehyde is catalyzed by ADH. Isolation of a Methanobacterium-like strain with ethanol showed that the ability to use primary alcohols also occurs in genera other than Methanogenium.
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  • 8
    ISSN: 1432-072X
    Keywords: Thermophilic Methanocoecus ; Deep sea hydrothermal vent methanogen ; Plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An extremely thermophilic methanogen was isolated from a hydrothermal vent core sample from Guaymas Basin, Gulf of California, at a depth of 2003 m. The isolate, designated strain AG86, was a coccoid autotroph using H2-CO2 as energy and carbon source with a growth temperature range of 48 to 92°C, optimum, 85°C. AG86 required NaCl and Mg2+ and trace amounts of selenite and tungstate. Vitamins were not required. However, yeast extract, Casamino acids and Trypticase stimulated growth significantly. When grown in the presence of these stimulants and at the optimal growth temperature and pH 6.5, the minimum doubling time was 20 min. Cells were fragile and readily lysed by detergents. The mol% G+C was 33%. These results and partial 16S rRNA sequencing indicated that AG86 belonged to the genus Methanococcus and closely resembled Methanococcus jannaschii. Tests for extrachromosomal DNA revealed a plasmid in AG86 and two plasmids in M. jannaschii. Different patterns were obtained from restriction endonuclease digestion of the three plasmids, and no homology was observed with DNA-DNA hybridization.
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  • 9
    ISSN: 1432-072X
    Keywords: Key words Phototrophic bacteria ; Photoheterotrophic growth ; Aromatic hydrocarbons ; Toluene ; Benzylsuccinate ; 16S rRNA sequence analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The capacity of anoxygenic phototrophic bacteria to utilize aromatic hydrocarbons was investigated in enrichment cultures with toluene. When mineral medium with toluene (provided in an inert carrier phase) was inoculated with activated sludge and incubated under infrared illumination (〉 750 nm), a red-to-brownish culture developed. Agar dilution series indicated the dominance of two types of phototrophic bacteria. One type formed red colonies, had rod-shaped cells with budding division, and grew on benzoate but not on toluene. The other type formed yellow-to-brown colonies, had oval cells, and utilized toluene and benzoate. One strain of the latter type, ToP1, was studied in detail. Sequence analysis of the 16S rRNA gene and DNA-DNA hybridization indicated an affiliation of strain ToP1 with the species Blastochloris sulfoviridis, a member of the α-subclass of Proteobacteria. However, the type strain (DSM 729) of Blc. sulfoviridis grew neither on toluene nor on benzoate. Light-dependent consumption of toluene in the presence of carbon dioxide and formation of cell mass by strain ToP1 were demonstrated in quantitative growth experiments. Strain ToP1 is the first phototrophic bacterium shown to utilize an aromatic hydrocarbon. In the supernatant of toluene-grown cultures and in cell-free extracts incubated with toluene and fumarate, the formation of benzylsuccinate was detected. These findings indicate that the phototrophic bacterium activates toluene anaerobically by the same mechanism that has been reported for denitrifying and sulfate-reducing bacteria. The natural abundance of phototrophic bacteria with the capacity for toluene utilization was examined in freshwater habitats. Counting series revealed that up to around 1% (1.8 × 105 cells per gram dry mass of sample) of the photoheterotrophic population cultivable with acetate grew on toluene.
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  • 10
    ISSN: 1432-072X
    Keywords: Desulfotomaculum ; Sulfate reduction ; Autotrophic growth ; Carbon dioxide reduction to acetate ; Hydrogen ; Carbon monoxide ; Methanol ; Fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth of Desulfotomaculum orientis, D. ruminis, D. nigrificans and the Desulfotomaculum strains TEP, TWC and TWP, that were newly isolated with sulfate and fatty acids, was studied using defined mineral media. Four of these strains grew with hydrogen plus sulfate as the only energy source. Under these conditions the growth yield of D. orientis in batch culture was 7.5 g cell dry mass per mol sulfate reduced. Growth on methanol with growth yields of about 6 g cell dry mass per mol sulfate was obtained with D. orientis and strain TEP. All strains tested grew slowly with formate as electron donor. Fatty acids from propionate to palmitate were utilized by the strains TEP, TWC and TWP. D. orientis and the strains TEP and TWC were able to utilize the methoxyl groups of trimethoxybenzoate for growth. D. orientis was found to grow chemoautotrophically with hydrogen, carbon dioxide and sulfate; during growth with C1-compounds no additional organic carbon source was required. Furthermore, D. orientis was able to grow slowly in sulfate-free medium with formate, methanol, ethanol lactate, pyruvate or trimethoxybenzoate. Under these conditions acetate was excreted, indicating the function of carbon dioxide as electron acceptor in a homoacetogenic process. A growth-promoting effect of pyrophosphate added to the medium of Desulfotomaculum species was not observed. The results show a high catabolic and anabolic versatility among Desulfotomaculum species, and indicate that electron transport to sulfate can be the sole energy conserving process in this genus.
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