Biomedical subjects

F Widdel

Publications and source records attributed to F Widdel.

28 records · Page 2Linked to original sources

PubMed1994

Anaerobic oxidation of hydrocarbons in crude oil by new types of sulphate-reducing bacteria.

Many crude oil constituents are biodegradable in the presence of oxygen; however, a substantial anaerobic degradation has never been demonstrated. An unusually low content of n-alkanes in oils of certain deposits is commonly attributed to selective utilization of these hydrocarbons by aerobic microorganisms. On the other hand, oil wells and production fluids were shown to harbour anaerobic sulphate-reducing bacteria, but their actual electron donors and carbon sources were unknown. On the basis of nutritional properties of various bacterial isolates it was assumed that fatty acids and H2 are potential electron donors for sulphate reduction in situ. Here we demonstrate that hydrocarbons in crude oil are used directly by sulphate-reducing bacteria growing under strictly anoxic conditions. A moderately thermophilic pure culture selectively utilizes n-alkanes in oil for sulphate reduction to sulphide. In addition, a mesophilic sulphate-reducing enrichment culture is shown to oxidize alkylbenzenes in oil. Thus, sulphate-reducing bacteria utilizing aliphatic and aromatic hydrocarbons as electron donors may present a significant source of sulphide in oil deposits and oil production plants.

Anaerobiosis↗

PubMed1994

Anaerobic oxidation of ferrous iron by purple bacteria, a new type of phototrophic metabolism.

Anoxic iron-rich sediment samples that had been stored in the light showed development of brown, rusty patches. Subcultures in defined mineral media with ferrous iron (10 mmol/liter, mostly precipitated as FeCO3) yielded enrichments of anoxygenic phototrophic bacteria which used ferrous iron as the sole electron donor for photosynthesis. Two different types of purple bacteria, represented by strains L7 and SW2, were isolated which oxidized colorless ferrous iron under anoxic conditions in the light to brown ferric iron. Strain L7 had rod-shaped, nonmotile cells (1.3 by 2 to 3 microns) which frequently formed gas vesicles. In addition to ferrous iron, strain L7 used H2 + CO2, acetate, pyruvate, and glucose as substrate for phototrophic growth. Strain SW2 had small rod-shaped, nonmotile cells (0.5 by 1 to 1.5 microns). Besides ferrous iron, strain SW2 utilized H2 + CO2, monocarboxylic acids, glucose, and fructose. Neither strain utilized free sulfide; however, both strains grew on black ferrous sulfide (FeS) which was converted to ferric iron and sulfate. Strains L7 and SW2 grown photoheterotrophically without ferrous iron were purple to brownish red and yellowish brown, respectively; absorption spectra revealed peaks characteristic of bacteriochlorophyll a. The closest phototrophic relatives of strains L7 and SW2 so far examined on the basis of 16S rRNA sequences were species of the genera Chromatium (gamma subclass of proteobacteria) and Rhodobacter (alpha subclass), respectively. In mineral medium, the new isolates formed 7.6 g of cell dry mass per mol of Fe(II) oxidized, which is in good agreement with a photoautotrophic utilization of ferrous iron as electron donor for CO2 fixation. Dependence of ferrous iron oxidation on light and CO2 was also demonstrated in dense cell suspensions. In media containing both ferrous iron and an organic substrate (e.g., acetate, glucose), strain L7 utilized ferrous iron and the organic compound simultaneously; in contrast, strain SW2 started to oxidize ferrous iron only after consumption of the organic electron donor. Ferrous iron oxidation by anoxygenic phototrophs is understandable in terms of energetics. In contrast to the Fe3+/Fe2+ pair (E0 = +0.77 V) existing in acidic solutions, the relevant redox pair at pH 7 in bicarbonate-containing environments, Fe(OH)3 + HCO3-/FeCO3, has an E0' of +0.2 V. Ferrous iron at pH 7 can therefore donate electrons to the photosystem of anoxygenic phototrophs, which in purple bacteria has a midpoint potential around +0.45 V. The existence of ferrous iron-oxidizing anoxygenic phototrophs may offer an explanation for the deposition of early banded-iron formations in an assumed anoxic biosphere in Archean times.

Anaerobiosis↗

PubMed1993

Complete oxidation of toluene under strictly anoxic conditions by a new sulfate-reducing bacterium.

A toluene-degrading sulfate-reducing bacterium, strain Tol2, was isolated from marine sediment under strictly anoxic conditions. Toluene was toxic if applied directly to the medium at concentrations higher than 0.5 mM. To provide toluene continuously at a nontoxic concentration, it was supplied in an inert hydrophobic carrier phase. The isolate had oval, sometimes motile cells (1.2 to 1.4 by 1.2 to 2.0 microns). The doubling time was 27 h. Toluene was completely oxidized to CO2, as demonstrated by measurement of the degradation balance. The presence of carbon monoxide dehydrogenase and formate dehydrogenase indicated a terminal oxidation of acetyl coenzyme A via the CO dehydrogenase pathway. The use of hypothetical intermediates of toluene degradation was tested in growth experiments and adaptation studies with dense cell suspensions. Results do not support a degradation of toluene via one of the cresols or methylbenzoates, benzyl alcohol, or phenylacetate as free intermediate. Benzyl alcohol did not serve as growth substrate; moreover, it was a strong, specific inhibitor of toluene degradation, whereas benzoate utilization was not affected by benzyl alcohol. Sequencing of 16S rRNA revealed a relationship to the metabolically dissimilar genus Desulfobacter and on a deeper level to the genus Desulfobacterium. The new genus and species Desulfobacula toluolica is proposed.

Anaerobiosis↗

PubMed1992

Structure determination of two new amino acid-containing derivatives of adenosine from tRNA of thermophilic bacteria and archaea.

Two new nucleosides have been identified in unfractionated transfer RNA of two thermophilic bacteria, Thermodesulfobacterium commune, and Thermotoga maritima, six hyperthermophilic archaea, including Pyrobaculum islandicum, Pyrococcus furiosus and Thermococcus sp. and two mesophilic archaea, Methanococcus vannielii and Methanolobus tindarius. Structures were determined primarily by mass spectrometry, as 3-hydroxy-N-[[(9-beta-D-ribofuranosyl-9H-purin-6- yl)amino]carbonyl]norvaline, (hn6A), structure 1, and 3-hydroxy-N-[[(9-beta-D-ribofuranosyl-9H-2-methylthiopurin-6- yl)amino]carbonyl]norvaline (ms2hn6A), 2. The amino acid side chain was characterized as 3-hydroxynorvaline (3) by gas chromatography-mass spectrometry of the trimethylsilyl derivative after cleavage from 1 and 2 by alkaline hydrolysis. Evidence for the amino acid-purine carbamoyl linkage was obtained from the collision-induced dissociation mass spectrum of trimethylsilylated 1, and the total structure was confirmed by chemical synthesis of 1.

Adenosine↗

PubMed1989

Natural relationships among sulfate-reducing eubacteria.

Phylogenetic relationships among 20 nonsporeforming and two endospore-forming species of sulfate-reducing eubacteria were inferred from comparative 16S rRNA sequencing. All genera of mesophilic sulfate-reducing eubacteria except the new genus Desulfomicrobium and the gliding Desulfonema species were included. The sporeforming species Desulfotomaculum ruminis and Desulfotomaculum orientis were found to be gram-positive organisms sharing 83% 16S rRNA sequence similarity, indicating that this genus is diverse. The gram-negative nonsporeforming species could be divided into seven natural groups: group 1, Desulfovibrio desulfuricans and other species of this genus that do not degrade fatty acids (this group also included "Desulfomonas" pigra); group 2, the fatty acid-degrading "Desulfovibrio" sapovorans; group 3, Desulfobulbus species; group 4, Desulfobacter species; group 5, Desulfobacterium species and "Desulfococcus" niacini; group 6, Desulfococcus multivorans and Desulfosarcina variabilis; and group 7, the fatty acid-oxidizing "Desulfovibrio" baarsii. (The quotation marks are used to indicate the need for taxonomic revision.) Groups 1 to 3 are incomplete oxidizers that form acetate as an end product; groups 4 to 7 are complete oxidizers. The data were consistent with and refined relationships previously inferred by oligonucleotide catalogs of 16S rRNA. Although the determined relationships are generally consistent with the existing classification based on physiology and other characteristics, the need for some taxonomic revision is indicated.

Base Sequence↗

PubMed1986

Growth of methanogenic bacteria in pure culture with 2-propanol and other alcohols as hydrogen donors.

Two types of mesophilic, methanogenic bacteria were isolated in pure culture from anaerobic freshwater and marine mud with 2-propanol as the hydrogen donor. The freshwater strain (SK) was a Methanospirillum species, the marine, salt-requiring strain (CV), which had irregular coccoid cells, resembled Methanogenium sp. Stoichiometric measurements revealed formation of 1 mol of CH(4) by CO(2) reduction, with 4 mol of 2-propanol being converted to acetone. In addition to 2-propanol, the isolates used 2-butanol, H(2), or formate but not methanol or polyols. Acetate did not serve as an energy substrate but was necessary as a carbon source. Strain CV also oxidized ethanol or 1-propanol to acetate or propionate, respectively; growth on the latter alcohols was slower, but final cell densities were about threefold higher than on 2-propanol. Both strains grew well in defined, bicarbonate-buffered, sulfide-reduced media. For cultivation of strain CV, additions of biotin, vitamin B(12), and tungstate were necessary. The newly isolated strains are the first methanogens that were shown to grow in pure culture with alcohols other than methanol. Bioenergetic aspects of secondary and primary alcohol utilization by methanogens are discussed.

Journal Article↗

PubMed1982

The bacteria of the sulphur cycle.

This paper concentrates on the bacteria involved in the reductions and oxidations of inorganic sulphur compounds under anaerobic conditions. The genera of the dissimilatory sulphate-reducing bacteria known today are discussed with respect to their different capacities to decompose and oxidize various products of fermentative degradations of organic matter. The utilization of molecular hydrogen and formate by sulphate reducers shifts fermentations towards the energetically more favourable formation of acetate. Since acetate amounts to about two-thirds of the degradation products of organic matter, the complete anaerobic oxidation of acetate by several genera of the sulphate-reducing bacteria is an important function for terminal oxidation in sulphate-sufficient environments. The results of pure culture studies agree well with ecological investigations of several authors who showed the significance of sulphate reduction for the complete oxidation of organic matter in anaerobic marine habitats. In the dissimilatory sulphur-reducing bacteria of the genus Desulfuromonas the oxidation of acetate is linked to the reduction of elemental sulphur. Major characteristics of the anaerobic, sulphide-oxidizing phototrophic green and purple sulphur bacteria as well as of some facultative anoxygenic cyanobacteria, are given. By the formation of elemental sulphur and sulphate, these bacteria establish sulphur cycles with the sulphide-forming bacteria. In view of the morphological diversity of the sulphate-reducing bacteria and question of possible evolutionary relations to phototrophic sulphur bacteria is raised.

Bacteria↗

PubMed1981

Studies on dissimilatory sulfate-reducing bacteria that decompose fatty acids. I. Isolation of new sulfate-reducing bacteria enriched with acetate from saline environments. Description of Desulfobacter postgatei gen. nov., sp. nov.

Three strains (2ac9, 3ac10 and 4ac11) of oval to rod-shaped, Gram negative, nonsporing sulfate-reducing bacteria were isolated from brackish water and marine mud samples with acetate as sole electron donor. All three strains grew in simple defined media supplemented with biotin and 4-aminobenzoic acid as growth factors. Acetate was the only electron donor utilized by strain 2ac9, while the other two strains used in addition ethanol and/or lactate. Sulfate served as electron acceptor and was reduced to H2S. Complete oxidation of acetate to CO2 was shown by stoichiometric measurements with strain 2ac9 in batch cultures using sulfate, sulfite or thiosulfate as electron acceptors. With sulfate an average growth yield of 4.8 g cell dry weight was obtained per mol of acetate oxidized; with sulfite or thiosulfate the growth yield on acetate was about twice as high. None of the strains contained desulfoviridin. In strain 2ac9 cytochromes of the b- and c-type were detected. Strain 2ac9 is described as type strain of the new species and genus, Desulfobacter postgatei.

Acetates↗

PubMed1981

Sporulation and further nutritional characteristics of Desulfotomaculum acetoxidans.

Acetate-oxidizing sulfate-reducing bacteria of the Desulfotomaculum acetoxidans type have been enriched from animal manure, rumen content and dung contaminated freshwater habitats, indicating that they are primarily intestinal bacteria. Sporulation was observed only when acetate was the organic substrate; with butyrate, which allowed faster growth than acetate, spore formation never occurred. The cone-shaped highly refractile areas adjacent to the spores in spore-forming mother cells were shown to be gas vacuoles. Biotin was the only growth factor required by Desulfotomaculum acetoxidans strain 5575 in minimal media with sulfate and acetate or other organic substrates.

Acetates↗

PubMed1977

A new anaerobic, sporing, acetate-oxidizing, sulfate-reducing bacterium, Desulfotomaculum (emend.) acetoxidans.

A new strictly anaerobic, polarly flagellated, sporing, acetate-oxidizing, sulfate-reducing bacterium was isolated from anaerobic fresh or sea water mud samples. The oxidation of acetate to CO2 is stoichiometrically linked to the formation of H2S from sulfate. Ethanol, butanol and butyrate are also used. Hydrogen, lactate or pyruvate are not used as electron donors; organic substances are not fermented. A cytochrome of the b-type and a supposed sulfite reductase, P582, were detected spectrophotometrically. An emended description of the genus Desulfotomaculum is proposed which includes the new bacterium as the species Desulfotomaculum acetoxidans.

Acetates↗