Tetrachloroethylene as electron acceptor for the anaerobic degradation of benzoate

Abstract Teltrachloroethylene (PCE) was biotransformed by reductive dehalgenation under anoxic conditions with benzoate as the electron donor. The experiments were carried out under batch culture conditions with biomass from an anoxic fixed bed reactor fed with benzoate and PCE. Inhibition of methanogenesis by bromoethane-sulfonic acid (BES) resulted in a complete inhibition of benzoate degradation. Benzoate, however, was decomposed in the presence of BES if PCE was added to the cultures. With 2.8 mmol/1 PCE, that was transformed to 1.4 mmol/1 cis-1,2-dichloroethylene (DCE) and 3.8 mmol/1 chloride, 2 mmol/1 benzoate were degraded to about 3.2 mmol/1 acetate. The elimination of benzoate was directly proportional to DCE accumulation, ranging between 1:0.5 and 1:1.     

Amperometric method for monitoring anaerobic respiration with nitrous oxide as the terminal electron acceptor

A commercially available Clark-type electrode with a platinum cathode, commonly used for monitoring oxygen uptake, may also be used to monitor respiration with N₂O. The disadvantages of this system include a high sensitivity to O₂, which may be overcome by excluding O₂, and sensitivity to acetylene. The advantage of the method is that it may be used to monitor directly the reduction of N₂O by respiring cells.     

Trimethylamine oxide: a terminal electron acceptor in anaerobic respiration of bacteria.

Trimethylamine oxide (TMAO) stimulated both the anaerobic growth rate and the growth yield of Proteus NTHC 153. The molar growth yield from glucose and pyruvate in tryptone/yeast extract medium doubled in the presence of TMAO, and the organism grew anaerobically on the non-fermentable substrates L-lactate and formate when TMAO was added to the medium. We conclude that TMAO stimulated growth by serving as a terminal electron acceptor in an oxidative phosphorylation process.     

Stimulating the anaerobic degradation of aromatic hydrocarbons in contaminated sediments by providing an electrode as the electron acceptor

The possibility that electrodes might serve as an electron acceptor to simulate the degradation of aromatic hydrocarbons in anaerobic contaminated sediments was investigated. Initial studies with Geobacter metallireducens demonstrated that although toluene was rapidly adsorbed onto the graphite electrodes it was rapidly oxidized to carbon dioxide with the electrode serving as the sole electron acceptor. Providing graphite electrodes as an electron acceptor in hydrocarbon‐contaminated sediments significantly stimulated the removal of added toluene and benzene. Rates of toluene and benzene removal accelerated with continued additions of toluene and benzene. [¹⁴C]‐Toluene and [¹⁴C]‐benzene were quantitatively recovered as [¹⁴C]‐CO₂, demonstrating that even though the graphite adsorbed toluene and benzene they were degraded. Introducing an electrode as an electron acceptor also accelerated the loss of added naphthalene and [¹⁴C]‐naphthalene was converted to [¹⁴C]‐CO₂. The results suggest that graphite electrodes can serve as an electron acceptor for the degradation of aromatic hydrocarbon contaminants in sediments, co‐localizing the contaminants, the degradative organisms and the electron acceptor. Once in position, they provide a permanent, low‐maintenance source of electron acceptor. Thus, graphite electrodes may offer an attractive alternative for enhancing contaminant degradation in anoxic environments.     

Metabolic profiles and aprE expression in anaerobic cultures of Bacillus subtilis using nitrate as terminal electron acceptor

Cultures using nitrate as the terminal electron acceptor were conducted in Schaeffer's medium to evaluate the growth performance and metabolic profiles of Bacillus subtilis, and its potential to express the aprE (subtilisin) gene under anoxic conditions. Nitrate was converted to ammonia through nitrite reduction; and different product profiles were observed during the growth phase when nitrate was added at various concentrations (4-24 mM) to Schaeffer's medium containing glucose (4 g l(-1)). If nitrate was not limiting, then acetic acid and acetoin were accumulated, suggesting a limitation of reduced cofactors but, if nitrate became limiting, then lactic acid and butanediol were accumulated, suggesting an excess of reduced cofactors. Due to a strong lysis at the onset of the end of the growth phase, sporulation frequency and aprE expression were negligible in anaerobic batch cultures. Fed-batch fermentation allowed the development of a stationary phase through a continuous supply of glucose and nitrate. In this case, sporulation frequency was almost null, but interestingly aprE expression was similar to that found in aerobic cultures.     

Metabolomic analyses show that electron donor and acceptor ratios control anaerobic electron transfer pathways in Shewanella oneidensis

This study investigated the physiological impact of changing electron donor–acceptor ratios on electron transfer pathways in the metabolically flexible subsurface bacterium Shewanella oneidensis, using batch and chemostat cultures, with an azo dye (ramazol black B) as the model electron acceptor. Altering the growth rate did result in changes in biomass yield, but not in other key physiological parameters including the total cytochrome content of the cells, the production of extracellular flavin redox shuttles or the potential of the organism to reduce the azo dye. Dramatic increases in the ability to reduce the dye were noted when cells were grown under conditions of electron acceptor (fumarate) limitation, although the yields of extracellular redox mediators (flavins) were similar under conditions of electron donor (lactate) or acceptor limitation. FT-IR spectroscopy confirmed shifts in the metabolic fingerprints of cells grown under these contrasting conditions, while spectrophotometric analyses supported a critical role for c-type cytochromes, expressed at maximal concentrations under conditions of electron acceptor limitation. Finally, key intracellular metabolites were quantified in batch experiments at various electron donor and acceptor ratios and analysed using discriminant analysis and a Bayesian network to construct a central metabolic pathway model for cells grown under conditions of electron donor or acceptor limitation. These results have identified key mechanisms involved in controlling electron transfer in Shewanella species, and have highlighted strategies to maximise reductive activity for a range of bioprocesses.     

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

1. With fumarate as the terminal electron acceptor and either H₂ or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.
2. Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.
3. Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.
4. In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.
5. During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H₂ or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO₂.
6. The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H₂ or formate were not detected in the bacterium.

     

Molecular oxygen as electron acceptor in the NADH-nitrate reductase system

This paper describes first experimental evidence that dissolved molecular oxygen acts as an electron acceptor in the NADH-nitrate reductase system. The molecular mechanism and possible physiological implications on the induction mechanism of nitrate reductase by nitrate ion are discussed.     

Failure of denitrifying bacteria to utilize benzoic acid under anaerobic conditions with nitrate as the only terminal electron acceptor

Summary (Ring-U)-¹⁴C-benzoate was not utilized by various denitrifying bacteria (pure cultures of Pseudomonas aeruginosa, Acinetobacter sp. and Moraxella sp. or a mixed population) in the presence of nitrate as the only electron acceptor (completely anaerobic conditions). In the presence of only traces of molecular oxygen (introduced by porous tubing), denitrification did occur under inappropriate experimental conditions. This indicates that an apparent anaerobic fission of the benzene nucleus may occur.     

Growth of the yeast Hansenula anomala with nitrate as sole source of nitrogen under aerobic and anaerobic conditions

Summary The oxygen requirement ofHansenula anomala growing in batch culture on nitrate as sole source of nitrogen was examined. An aeration rate of 0.03 vvm or a constant oxygen partial pressure of 0.01 bar is sufficient for optimal growth.     

Fe(III) as an electron acceptor for H2 oxidation in thermophilic anaerobic enrichment cultures from geothermal areas

Six sustainable enrichment cultures of thermophilic H₂-oxidizing microorganisms utilizing Fe(III) as an electron acceptor were obtained from geothermally heated environments located on two continents (America, Eurasia) and on islands in the Northern (Iceland) and Southern (Fiji) hemispheres, demonstrating the wide distribution of these microorganisms. The main products of amorphic Fe(III) oxide reduction were magnetite and siderite. The observed temperature range for Fe(III) reduction in growing cultures was from 55°C to 87°C, extending the known limits for growth of Fe(III)-reducing microorganisms producing extracellular magnetite to nearly 90°C. Received: August 13, 1996 / Accepted: January 17, 1997     

Rhein as an electron acceptor for various flavoproteins and for electron transport particles

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) which has been previously employed as an inhibitor for electron transport particles, NADH dehydrogenase, and other flavoproteins is reducible under physiological conditions. Soluble hydrogenase from Alcaligenes eutrophus H 16, several flavoproteins, and electron transport particles from baker's yeast and from beef heart were found to catalyse NADH oxidation with 9 micrometers to 2mM rhein as the electron acceptor. Dithionite or enzymatically reduced rhein (lambda max = 408 nm) is immediately reoxidized to rhein lambda max = 437 nm) by oxygen. Cyclovoltagrams reveal the midpoint redox potentials --0.240 V, -0.270 V, -0.280 V, -0.335 V at pH 6.0, 7.0, 7.7, 9.2, respectively. Due to its redox behaviour, caution should be exercised using rhein as a flavin-site-directed inhibitor for biological electron transfer systems.     

Reduced sulfur and nitrogen compounds and molecular hydrogen as electron donors for anaerobic CO2 photoreduction in Anacystis nidulans

Photosynthesis by Anacystis nidulans was studied in presence of reduced sulfur or nitrogen compounds, or of hydrogen. O₂ evolution and CO₂ fixation were depressed by sulfide, sulfite, cysteine, thioglycollate, hydroxylamine and hydrazine. Sulfite, cysteine and hydrazine inhibited O₂ evolution much more strongly than CO₂ fixation, indicating ability to supply electrons for CO₂ photoreduction; DCMU suppressed these photoreductions. In contrast, some anoxygenic photosynthetic CO₂ fixation insensitive to DCMU was found with sulfide, thiosulfate and hydrogen. Emerson enhancement studies confirmed that sulfite, cysteine and hydrazine acted on photosystem II, while photoreduction supported by sulfide, thiosulfate and hydrogen needed photosystem I only.Sulfite was photooxidized to sulfate, sulfide to elemental sulfur, and thiosulfate to sulfate plus elemental sulfur; the sulfur accumulated inside the cells. Results on the stoichiometries of the photoreductions were consistent with the photooxidation products determined. Inhibitor studies suggested photosynthetic CO₂ fixation through the Calvin cycle.While photoreduction by all reductants used was found to be constitutive in Anacystis, the process was stimulated by anaerobic preincubation with the reductants only in the cases of hydrogen and thiosulfate; this adaptation was prevented by chloramphenicol and by O₂. Anaerobic photoautotrophic growth of Anacystis was, however, not observed; the increase in dry weight with H₂ and thiosulfate was not accompanied by cell multiplication or by an increase in chlorophyll content. Parallel short-term experiments with Chlorella did not reveal any constitutive photoreduction in this eukaryotic alga.Abbreviations CAP chloramphenicol - CCCP carbonyl cyanide m-chlorophenylhydrazone - DBMIB dibromothymoquinone - DCMU dichlorophenyl dimethyl urea - DSPD disalicylidenepropane diamine-(1,3) - EDAC 1-ethyl-3(3-dimethylaminopropyl-) carbodiimide