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PubMed1976

Anaerobic transport of amino acids coupled to the glycerol-3-phosphate-fumarate oxidoreductase system in a cytochrome-deficient mutant of Escherichia coli.

The uptake of proline and glutamine by cytochrome-deficient cells of Escherichia coli SASX76 grown aerobically on glucose or anaerobically on pyruvate was stimulated by these two substrates. Pyruvate could not stimulate transport in the glucose-grown cells. Uptake of these amino acids energized by glucose was inhibited by inhibitors of the Ca2+, Mg2+-stimulated ATPase such as DCCD, pyrophosphate, and azide, and by the uncouplers CCCP and 2,4-dinitrophenol. Glycerol (or glycerol 3-phosphate) in the presence of fumarate stimulated the transport of proline and glutamine under anaerobic conditions in cytochrome-deficient cells but not in membrane vesicles prepared from these cells although glycerol 3-phosphate-fumarate oxidoreductase activity could be demonstrated in the vesicle preparation. In contrast, in vesicles prepared from cytochrome-containing cells of E. coli SASX76 amino acid transport was energized under anaerobic conditions by this system. Inhibitors of the Ca2+, Mg2+-activated ATPase and uncoupling agents inhibited the uptake of proline and glutamine in cytochrome-deficient cells dependent on the glycerol-fumarate oxidoreductase system. Ferricyanide could replace fumarate as an electron acceptor to permit transport of phenylalanine in cytochrome-deficient or cytochrome-containing cells under anaerobic conditions. It is concluded that in cytochrome-deficient cells using glucose, pyruvate, or glycerol in the presence of fumarate, transport of both proline and glutamine under under anaerobic conditions is energized by ATP through the Ca2+, Mg2+-activated ATPase. In cytochrome-containing cells under anaerobic conditions electron transfer between glycerol and fumarate can also drive transport of these amino acids.

Adenosine Triphosphatases↗

PubMed1980

Isolation and functional aspects of the fumarate reductase involved in the phosphorylative electron transport of Vibrio succinogenes.

1. The fumarate reductase of Vibrio succinogenes, the terminal component of the electron transport chain of the bacterium, was extracted from the cytoplasmic membrane with Triton X=100 and purified to homogeneity (approx. 30-fold) by means of chromatograhy on hydroxyapatite and DEAE-Sephadex. The enzyme eluted from the ion-exchange column in two forms, one containing and the other lacking cytochrome b. 2. The enzyme lacking cytochrome b consisted of two peptides (Mr 79 000 and 31 000) which were present in a molar ratio of 1:1. The cytochrome-containing species contained an additional peptide (Mr 25 000) which was present in twice the molar amount of the others (2:1:1). 3. The hydrodynamic properties indicate that the functional enzymes consist of only one set of the corresponding peptides. 4. Each of the two enzyme molecules contains one protein-bound FAD which is linked to the Mr 79 000 peptide. Both enzyme species contain 9-10 mol iron-sulfur per mol of FAD which is associated with the Mr 79 000 and the Mr 31 000 peptide. Cytochrome b is present in an amount of 2 mol/mol of FAD, half of the cytochrome b has a midpoint potential of -20 mV. 5. The enzyme catalyzed two types of reaction. (a) Fumarate reduction by viologen radicals or anthrahydroquinonesulfonate, as well as succinate oxidation by ferricyanide or methylene blue, was independent of cytochrome b. (b) The activities of fumarate reduction by naphthohydroquinones and those of succinate oxidation by naphthoquinones were cytochrome b-dependent. This indicates that the electron transport from menaquinone to fumarate reductase in the membrane of the bacterium is mediated by a single component, cytochrome b (-20 mV). 6. The Km for fumarate was 0.35 mM with menadiol as the donor and that for succinate as 20 mM in the reverse reaction. Succinate oxidation was competitively inhibited by fumarate with a Ki of 0.35 mM.

Cell Membrane↗

PubMed1987

Possible role of the NADH-fumarate reductase in superoxide anion and hydrogen peroxide production in Trypanosoma brucei.

Mitochondrial membranes from Trypanosoma brucei procyclic trypomastigotes generated superoxide anion and hydrogen peroxide in a 2:1 ratio when supplemented with NADH. Fumarate inhibited hydrogen peroxide formation (Ki = 16 microM) with the same affinity as it stimulated NADH-fumarate reductase activity. Superoxide anion production was also 65% inhibited by fumarate (Ki = 20 microM). The KM for NADH of the NADH-fumarate reductase (60 microM) was also similar to that for hydrogen peroxide generation in the absence of fumarate (30 microM). These results suggest that the NADH-fumarate reductase is involved as a source for free radical generation in T. brucei mitochondria.

Animals↗

PubMed2002

Fumarate respiration of Wolinella succinogenes: enzymology, energetics and coupling mechanism.

Wolinella succinogenes performs oxidative phosphorylation with fumarate instead of O2 as terminal electron acceptor and H2 or formate as electron donors. Fumarate reduction by these donors ('fumarate respiration') is catalyzed by an electron transport chain in the bacterial membrane, and is coupled to the generation of an electrochemical proton potential (Deltap) across the bacterial membrane. The experimental evidence concerning the electron transport and its coupling to Deltap generation is reviewed in this article. The electron transport chain consists of fumarate reductase, menaquinone (MK) and either hydrogenase or formate dehydrogenase. Measurements indicate that the Deltap is generated exclusively by MK reduction with H2 or formate; MKH2 oxidation by fumarate appears to be an electroneutral process. However, evidence derived from the crystal structure of fumarate reductase suggests an electrogenic mechanism for the latter process.

Bacillus subtilis↗

PubMed1993

Reversible electrochemistry of fumarate reductase immobilized on an electrode surface. Direct voltammetric observations of redox centers and their participation in rapid catalytic electron transport.

Fumarate reductase (Escherichia coli) can be immobilized in an extremely electroactive state at an electrode, with retention of native catalytic properties. The membrane-extrinsic FrdAB component adsorbs to monolayer coverage at edge-oriented pyrolytic graphite and catalyzes reduction of fumarate or oxidation of succinate, depending upon the electrode potential. In the absence of substrates, reversible redox transformations of centers in the enzyme are observed by cyclic voltammetry. The major component of the voltammograms is a pair of narrow reduction and oxidation signals corresponding to a pH-sensitive couple with formal reduction potential E degree' = -48 mV vs SHE at pH 7.0 (25 degrees C). This is assigned to two-electron reduction and oxidation of the active-site FAD. A redox couple with E degree' = -311 mV at pH 7 is assigned to center 2 ([4Fe-4S]2+/1+). Voltammograms for fumarate reduction at 25 degrees C, measured with a rotating-disk electrode, show high catalytic activity without the low-potential switch-off that is observed for the related enzyme succinate dehydrogenase. The catalytic electrochemistry is interpreted in terms of a basic model incorporating mass transport of substrate, interfacial electron transfer, and intrinsic kinetic properties of the enzyme, each of these becoming a rate-determining factor under certain conditions. Electrochemical reversibility is approached under conditions of low turnover rate, for example, as the supply of substrate to the active site is limited. In this situation, electrocatalytic half-wave potentials, E1/2, are similar for oxidation of bulk succinate and reduction of bulk fumarate and coincide closely with the E degree' value assigned to the FAD. At 25 degrees C and pH 7, the apparent KM for fumarate reduction is 0.16 mM, and kcat is 840 s-1. Accordingly the second-order rate constant, kcat/KM, is 5.3 x 10(6) M-1 s-1. Under the same conditions, oxidation of succinate is much slower. As the supply of fumarate to the enzyme is raised to increase turnover, the electrochemical reaction eventually becomes limited by the rate of electron transfer from the electrode. Under these conditions a second catalytic wave becomes evident, the E1/2 value of which corresponds to the reduction potential of the redox couple suggested to be center 2. This small boost to the catalytic current indicates that the low-potential [4Fe-4S] cluster can function as a second center for relaying electrons to the FAD.

Adsorption↗

PubMed2001

Probing the active site of L-aspartate oxidase by site-directed mutagenesis: role of basic residues in fumarate reduction.

L-Aspartate oxidase is a very particular oxidase which behaves as a fumarate reductase in anaerobic conditions. Its primary and tertiary structures present remarkable similarity with the soluble fumarate reductase (FRD) from Shewanella frigidimarina and the flavin subunit of the membrane-bound fumarate reductase from Escherichia coli and Wolinella succinogenes. This and other extensive similarities are consistent with the idea that a common catalytic mechanism for the reduction of fumarate operates for all members of this enzyme group and that the key residues involved in the substrate binding and catalysis are conserved. This manuscript reports information about the role of these basic residues in L-aspartate oxidase: R290, R386, H244, and H351. By means of site-directed mutagenesis, R290 and R386 are mutated to Leu and H351 and H244 are mutated both to Ala and Ser. H351, H244, and R386 mutants bind substrate analogues with higher dissociation constants and present lower k(cat)/K(m) values in the reduction of fumarate. Therefore, the results indicate that R386, H244, and H351 are important for the binding of the substrate fumarate and may play an important but not essential role in catalysis. R290, on the contrary, is mainly involved in catalysis and not in substrate binding since its mutation abolishes the catalytic activity without lowering the affinity of the enzyme for the substrate. The redox properties of all the mutants are identical to the wild-type. The findings are consistent with a model of L-aspartate oxidase active site based on the hypothesis proposed for the soluble FRD from S. fridimarina.

Alanine↗

PubMed1999

Transport and metabolism of exogenous fumarate and 3-phosphoglycerate in vascular smooth muscle.

The keto (linear) form of exogenous fructose 1,6-bisphosphate, a highly charged glycolytic intermediate, may utilize a dicarboxylate transporter to cross the cell membrane, support glycolysis, and produce ATP anaerobically. We tested the hypothesis that fumarate, a dicarboxylate, and 3-phosphoglycerate (3-PG), an intermediate structurally similar to a dicarboxylate, can support contraction in vascular smooth muscle during hypoxia. To assess ATP production during hypoxia we measured isometric force maintenance in hog carotid arteries during hypoxia in the presence or absence of 20 mM fumarate or 3-PG. 3-PG improved maintenance of force (p < 0.05) during the 30-80 min period of hypoxia. Fumarate decreased peak isometric force development by 9.5% (p = 0.008) but modestly improved maintenance of force (p < 0.05) throughout the first 80 min of hypoxia. 13C-NMR on tissue extracts and superfusates revealed 1,2,3,4-(13)C-fumarate (5 mM) metabolism to 1,2,3,4-(13)C-malate under oxygenated and hypoxic conditions suggesting uptake and metabolism of fumarate. In conclusion, exogenous fumarate and 3-PG readily enter vascular smooth muscle cells, presumably by a dicarboxylate transporter, and support energetically important pathways.

Animals↗

PubMed1999

Structure and mechanism of the flavocytochrome c fumarate reductase of Shewanella putrefaciens MR-1.

Fumarate respiration is one of the most widespread types of anaerobic respiration. The soluble fumarate reductase of Shewanella putrefaciens MR-1 is a periplasmic tetraheme flavocytochrome c. The crystal structures of the enzyme were solved to 2.9 A for the uncomplexed form and to 2.8 A and 2.5 A for the fumarate and the succinate-bound protein, respectively. The structures reveal a flexible capping domain linked to the FAD-binding domain. A catalytic mechanism for fumarate reduction based on the structure of the complexed protein is proposed. The mechanism for the reverse reaction is a model for the homologous succinate dehydrogenase (complex II) of the respiratory chain. In flavocytochrome c fumarate reductase, all redox centers are in van der Waals contact with one another, thus providing an efficient conduit of electrons from the hemes via the FAD to fumarate.

Amino Acid Oxidoreductases↗

PubMed2002

Cerebral dicarboxylate transport and metabolism studied with isotopically labelled fumarate, malate and malonate.

Transport and metabolism of dicarboxylates may be important in the glial-neuronal metabolic interplay. Further, exogenous dicarboxylates have been suggested as cerebral energy substrates. After intrastriatal injection of [(14) C]fumarate or [(14) C]malate, glutamine attained a specific activity 4.1 and 2.6 times higher than that of glutamate, respectively, indicating predominantly glial uptake of these four-carbon dicarboxylates. In contrast, the three-carbon dicarboxylate [(14) C]malonate gave a specific activity in glutamate which was approximately five times higher than that of glutamine, indicating neuronal uptake of malonate. Therefore, neurones and glia take up different types of dicarboxylates, probably by different transport mechanisms. Labelling of alanine from [(14) C]fumarate and [(14) C]malate demonstrated extensive malate decarboxylation, presumably in glia. Intravenous injection of 75 micromol [U-(13) C]fumarate rapidly led to high concentrations of [U-(13) C]fumarate and [U-(13) C]malate in serum, but neither substrate labelled cerebral metabolites as determined by (13) C NMR spectroscopy. Only after conversion of [U-(13) C]fumarate into serum glucose was there (13) C-labelling of cerebral metabolites, and only at <10% of that obtained with 75 micromol [3-(13) C]lactate or [2-(13) C]acetate. These findings suggest a very low transport capacity for four-carbon dicarboxylates across the blood-brain barrier and rule out a role for exogenous fumarate as a cerebral energy substrate.

Acetates↗

PubMed1982

Cell and ATP yields of Citrobacter freundii growing with fumarate and H2 or formate in continuous culture.

Out of 19 strains belonging to the family Enterobacteriaceae only Escherichia coli and Citrobacter strains fermented fumarate exclusively to succinate. This fermentation was dependent on the presence of molecular hydrogen or formate. The inability of these micro-organisms to convert fumarate to succinate, acetate and CO2 correlated with their lack, or low activity, of oxaloacetate decarboxylase. Continuous culture experiments were performed with Citrobacter freundii in minimal or complex medium with fumarate + H2 of formate, and the growth parameters were determined. From the data obtained, a Ymax fumarate dissimilated value of 10.5 +/- 0.8 g dry wt per mol fumarate dissimilated was calculated. This value demonstrates that, per mol fumarate reduced, at least 0.6 +/- 0.05 mol ATP is produced and subsequently used for biosynthetic purposes.

Adenosine Triphosphate↗

PubMed2004

Pharmacokinetics of oral fumarates in healthy subjects.

AIMS: To characterize the pharmacokinetics of fumarates in healthy subjects. METHODS: Ten subjects received a single fumarate tablet (containing 120 mg of dimethylfumarate and 95 mg of calcium-monoethylfumarate) in the fasted state and after a standardized breakfast in randomized order. Prior to and at fixed intervals after the dose, blood samples were drawn and the concentrations of monomethylfumarate, the biologically active metabolite, as well as dimethylfumarate and fumaric acid were measured using high-performance liquid chromatography. RESULTS: After a lag time, a transient increase in serum monomethylfumarate concentrations in the blood was observed, whereas dimethylfumarate and fumaric acid concentrations remained below the detection limit. The tlag was 240 min [range 60-603 min; 95% confidence interval (CI) 139, 471] shorter when the tablet was taken after an overnight fast (90 min; range 60-120 min; 95% CI 66, 107) than when taken with breakfast (300 min; range 180-723 min; 95% CI 0, 1002). The tmax was 241 min (range 60-1189 min, 95% CI 53, 781) shorter when the tablet was taken after an overnight fast (182 min; range 120-240 min; 95% CI 146, 211) than when taken with breakfast (361 min; range 240-1429 min; 95% CI 0, 1062). The mean Cmax for monomethylfumarate in the blood of fasting subjects was to 0.84 mg l(-1) (range 0.37-1.29 mg l(-1); 95% CI 0.52, 1.07) and did not differ from that in fed subjects (0.48 mg l(-1); range 0-1.22 mg l(-1); 95% CI 0, 5.55). CONCLUSIONS: The pharmacokinetics of monomethylfumarate in healthy subjects after a single tablet of fumarate are highly variable, particularly after food intake. Further experiments exploring the pharmacokinetics of oral fumarates are warranted in order to elucidate the mechanisms underlying variability in response in patients.

Administration, Oral↗

PubMed1973

Enzyme complex which couples glycerol-3-phosphate dehydrogenation to fumarate reduction in Escherichia coli.

Anaerobic growth of Escherichia coli on glycerol as carbon source and fumarate as hydrogen acceptor results in the induction of both anaerobic sn-glycerol-3-phosphate (G3P) dehydrogenase and fumarate reductase. In previous studies, the G3P dehydrogenase was measured by the G3P-dependent reduction of a tetrazolium dye mediated by phenazine methosulfate in the presence of flavine mononucleotide and flavine adenine dinucleotide, and fumarate reductase was measured by the fumarate-dependent oxidation of reduced flavine mononucleotide. Results from the present study indicate that these two enzymes actually constitute a functional complex which is sedimentable at 200,000 x g in 2 h and which can catalyze the dehydrogenation of G3P at the expense of fumarate without any added cofactor. This coupling activity is not constituted by simply mixing an extract containing anaerobic G3P dehydrogenase with another extract containing fumarate reductase. Additional evidence for an organized complex is provided by the high degree of sensitivity of the coupled reaction to low concentrations of the detergents Triton X-100 and Emasol 1130 in comparison with the individual activities of the two component enzymes measured with the aid of artificial cofactors.

Anaerobiosis↗

PubMed1978

Electron transport phosphorylation coupled to fumarate reduction by H2- and Mg2+-dependent adenosine triphosphatase activity in extracts of the rumen anaerobe Vibrio succinogenes.

Vibrio succinogenes, an anaerobic bacterium, obtains its energy for growth from H2 or formate oxidation coupled to the reduction of fumarate to succinate. Membrane preparations have been obtained from this organism that catalyze the synthesis of ATP during H2 oxidation coupled to fumarate reduction. Esterification of orthophosphate is dependent on electron transfer, as evidenced by the requirement for both H2 and fumarate. Phosphorylation is also dependent on ADP and is destroyed by boiling the membrane preparations. H2 utilized for fumarate reduction and succinate formed are stoichiometric. The phosphorylation is markedly uncoupled by pentachlorophenol and gramicidin, but to a lesser extent by dinitrophenol and methyl viologen. 2-n-Heptyl-4-hydroxyquinoline-N-oxide causes severe inhibition of H2 oxidation as well as phosphorylation, but oligomycin or antimycin A has no demonstrable effect. Among several electron acceptors tested, significant phosphorylation is observed only with fumarate. A Mg2+-dependent adenosine triphosphatase activity is present in both the membrane and soluble protein fractions. Highest activity is obtained with ATP as the substrate, and considerably less activity is obtained with other nucleoside triphosphates. The possibility that phosphorylation during "fumarate respiration" may play an important physiological role in the growth of many anaerobic and facultatively anaerobic bacteria is discussed.

Adenosine Triphosphatases↗

PubMed1987

Regulation of Escherichia coli fumarate reductase (frdABCD) operon expression by respiratory electron acceptors and the fnr gene product.

The fumarate reductase enzyme complex, encoded by the frdABCD operon, allows Escherichia coli to utilize fumarate as a terminal electron acceptor for anaerobic oxidative phosphorylation. To analyze the expression of fumarate reductase, protein and operon fusions were constructed between the frdA and the lacZ genes and introduced onto the E. coli chromosome at the lambda attachment site. Expression of beta-galactosidase from either fusion was increased 10-fold during anaerobic versus aerobic cell growth, increased an additional 1.5-fold by the presence of fumarate, the substrate, and decreased 23-fold by nitrate, a preferred electron acceptor. The addition of trimethylamine-N-oxide as an electron acceptor did not significantly alter frdA'-'lacZ expression. Control of frd operon expression is therefore exerted at the transcriptional level in response to the availability of the electron acceptors oxygen, fumarate, and nitrate. Anaerobic induction of frdA'-'lacZ expression was impaired in an fnr mutant and was restored when the fnr+ gene was provided in trans, thus establishing that the fnr gene product, Fnr, is responsible for the anaerobic activation of frd operon expression. Nitrate repression of frdA'-'lacZ expression was observed under either aerobic or anaerobic cell growth conditions in both wild-type and fnr mutant strains, demonstrating that the mechanism for nitrate repression is independent of nitrate respiration and oxygen control imparted by Fnr. Studies performed with a fnr'-'lacZ protein fusion confirmed that the fnr gene is expressed both aerobically and anaerobically. A model is proposed for the regulation of frdABCD operon expression in response to the availability of the alternate terminal electron acceptors oxygen, nitrate, and fumarate.

Aerobiosis↗

PubMed1967

Mechanism of fumaric acid accumulation in Rhizopus nigricans.

It is doubtful that the glyoxylate bypass plays a significant role in the accumulation of fumaric acid by fungi, as has been postulated. In high glucose media, which favor fumarate production, isocitrate lyase (threo-D(s) isocitrate glyoxylate lyase), which is the key enzyme of the glyoxylate bypass, is strongly repressed. The specific activity of this enzyme remains low as long as glucose is present in the medium, even though fumarate formation proceeds at a high level. In addition, the activity of isocitrate lyase is inhibited by phosphoenolpyruvate, which would be formed from glucose. Alternatively, evidence is presented that bulk accumulation of fumaric acid under aerobic conditions in high glucose media takes place through a C(3) plus C(1) carbon dioxide fixation. CO(2) fixation was measured by the direct incorporation of NaHC(14)O(3) into fumaric acid, and by demonstrating that the specific radioactivity of fumaric acid formed from uniformly labeled C(14)-glucose was decreased in the presence of nonradioactive carbonate. The extent of decrease in specific radioactivity is in accord with a C(3) plus C(1) CO(2) fixation mechanism.

Carbon Isotopes↗

PubMed1997

Effects and metabolism of fumarate in the perfused rat heart. A 13C mass isotopomer study.

The cardioprotective effects of fumarate have been linked to its metabolism to succinate through both oxidative and reductive pathways. To date, the relative contribution of these pathways is a subject of controversy. To address this question, we designed a protocol with 13C substrates and took advantage of 13C isotopomer analysis by gas chromatography-mass spectrometry. Rat hearts were perfused with 11 mM glucose, 1 mM lactate, 0.2 mM pyruvate, 0.2 mM [1-13C]octanoate, and 0.04 or 0.4 mM [U-13C4]fumarate. On reoxygenation after 40 min of severe hypoxia, hearts perfused with 0.4 mM fumarate showed a better recovery of contractile function and released less lactate dehydrogenase (an index of cellular necrosis) than those perfused with 0.04 mM fumarate. The 13C data showed that, in hypoxic hearts, fumarate conversion to succinate occurred only through reduction, although it accounted for only 16% of total succinate release. Most of the succinate was formed through the oxidation of alpha-ketoglutarate or its precursors (50 +/- 5%) and by another yet-unidentified pathway (34 +/- 4%). These data show that, in a model of hypoxia-reoxygenation, the cardioprotective effects of fumarate were associated with its predominant metabolism to succinate through the reductive pathway.

Animals↗

PubMed1999

Bioconversion of fumarate to succinate using glycerol as a carbon source.

In this study, a facultative bacterium that converts fumarate to succinate at a high yield was isolated. The yield of bioconversion was enhanced about 1.2 times by addition of glucose into culture medium at an initial concentration of 6 g/L. When the initial cell density was high (2 g/L), the succinate produced at pH 7.0 for initial fumarate concentrations of 30, 50, 80, and 100 g/L were 29.3, 40.9, 63.6, and 82.5 g/L, respectively, showing an increase with the initial fumarate concentration. The high yield of 96.8%/mole of fumarate in just 4 h was obtained at the initial fumarate concentration of 30 g/L. Comparing these values to those obtained with low cell culture (0.2 g/L), we found that the amount of succinate produced was similar, but the production rate in the high cell culture was about three times higher than was the case in the low cell culture. This strain converted fumarate to succinate at a rate of 3.5 g/L.h under the sparge of CO2.

Biodegradation, Environmental↗

PubMed2002

Continuous production of succinic acid by a fumarate-reducing bacterium immobilized in a hollow-fiber bioreactor.

Enterococcus faecalis RKY1, a fumarate-reducing bacterium, was immobilized in an asymmetric hollow-fiber bioreactor (HFBR) for the continuous production of succinic acid. The cells were inoculated into the shell side of the HFBR, which was operated in transverse mode. Since the pH values in the HFBR declined during continuous operation to about 5.7, it was necessary to change the feed pH from 7.0 to 8.0 after 24 h of operation in order to enhance production of succinic acid. During continuous operation with a medium containing fumarate and glycerol, the productivity of succinate was 3.0-10.9 g/(L x h) with an initial concentration of 30 g/L of fumarate, 4.9-14.9 g/(L x h) with 50 g/L of fumarate, and 7.2-17.1 g/(L x h) with 80 g/L of fumarate for dilution rates between 0.1 and 0.4 h(-1). The maximum productivity of succinate obtained by the HFBR (17.1 g of succinate/[L x h]) was 1.7 times higher than that of the batch bioconversions (9.9 g of succinate/ [L x h]) with 80 g/L of fumarate. Furthermore, the long-term stability of the HFBR was demonstrated with a continuously efficient production of succinate for more than 15 d (360 h).

Bacteriological Techniques↗