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C Holliger

Publications and source records attributed to C Holliger.

At least 19 recordsLinked to original sources
PubMed1996

Anaerobic biodegradation of hydrocarbons.

Anaerobic biodegradation of aliphatic and aromatic hydrocarbons is a promising alternative to aerobic biodegradation treatments in bioremediation processes. It is now proven that, besides toluene, benzene and ethylbenzene can be oxidized under anaerobic redox conditions. Anaerobic bacteria have also been shown capable of utilizing substrates not only in the pure form, but also in complex hydrocarbon mixtures, such as crude oil. In addition, crucial steps in anaerobic treatment processes have been studied in vitro to better understand the enzymes involved in monoaromatic hydrocarbon degradation. Knowledge remains incomplete, however, about the anaerobic degradation of aliphatic and polycyclic aromatic hydrocarbons.

Anaerobiosis↗
PubMed1996

The proton/electron ration of the menaquinone-dependent electron transport from dihydrogen to tetrachloroethene in "Dehalobacter restrictus".

In the anaerobic respiration chain of "Dehalobacter restrictus," dihydrogen functioned as the electron donor and tetrachloroethene (PCE) functioned as the electron acceptor. The hydrogenase faced the periplasm, and the PCE reductase faced the cytoplasmic side of the membrane. Both activities were associated with the cytoplasmic membrane. UV spectroscopy showed that membrane-bound menaquinone (MQ) was reduced by oxidation of H2 and reoxidized by reduction of PCE, indicating that MQ functions as an electron mediator. Fast proton liberation (t1/2 = 6 +/- 2 s) during electron transport from H2 to PCE and to trichloroethene (TCE) after addition of either PCE or TCE to H2-saturated cells resulted in an extrapolated H+/e- ratio of 1.25 +/- 0.2. This ratio indicated that besides the formation of protons upon oxidation of H2, vectorial translocation of protons from the inside to the outside could also occur. Proton liberation was inhibited by carbonylcyanide m-chlorophenylhydrazone (CCCP), 2-n-heptyl-4-hydroxyquinoline N-oxide (HOQNO), and CuCl2. Fast proton liberation with an H+/e- ratio of 0.65 +/- 0.1 was obtained after addition of the MQ analog 2,3-dimethyl-1,4-naphthoquinone (DMN) as an oxidant pulse. This acidification was also inhibited by CCCP, HOQNO, and CuCl2. Oxidation of reduced DMN by PCE was not associated with fast acidification. The results with DMN indicate that the consumption and release of protons associated with redox reactions of MQ during electron transfer from H2 to PCE both occurred at the cytoplasmic side of the membrane. The PCE reductase was photoreversibly inactivated by 1-iodopropane, indicating that a corrinoid was involved in the PCE reduction.

Bacteria↗
PubMed1994

Reductive dehalogenation as a respiratory process.

Anaerobic bacteria can reductively dehalogenate aliphatic and aromatic halogenated compounds in a respiratory process. Only a few of these bacteria have been isolated in pure cultures. However, long acclimation periods, substrate specificity, high dehalogenation rates, and the possibility to enrich for the dehalogenation activity by subcultivation in media containing an electron donor indicate that many of the reductive dehalogenations in the environment are catalyzed by specific bacteria. Molecular hydrogen or formate appear to be good electron donors for the enrichment of such organisms. Furthermore, systems have to be employed which supply the cultures with the halogenated compounds beyond their toxicity level. All bacteria that are presently available in pure culture and grow with a halogenated compound as electron acceptor are members of new genera. Based on experimental results with the membrane-impermeable electron mediator methyl viologen, a model of the respiration system of Dehalobacter restrictus, a tetrachloroethene-dechlorinating bacterium, is presented. Further studies of the biochemistry and energetics of respiratory-dehalogenating strains will help to understand the mechanisms involved and perhaps reveal the evolutionary origin of the dehalogenating enzyme systems.

Anaerobiosis↗
PubMed1994

Physiological meaning and potential for application of reductive dechlorination by anaerobic bacteria.

The physiological meaning of reductive dechlorination reactions catalyzed by anaerobic bacteria can be explained as a co-metabolic activity or as a novel type of respiration. Co-metabolic activities have been found mainly with alkyl halides. They are non-specific reactions catalyzed by various enzyme systems of facultative as well as obligate anaerobic bacteria. In contrast, the reductive dechlorinations involved in metabolic respiration processes are very specific reactions. Only a limited number of alkyl and aryl chlorinated compounds is presently known to function as a terminal electron acceptor in a few, recently isolated bacteria. Metabolic dechlorination rates are in general several orders of magnitude higher than co-metabolic ones. Both reaction types are suitable for the anaerobic treatment of waste streams.

Bacteria, Anaerobic↗
PubMed1993

A highly purified enrichment culture couples the reductive dechlorination of tetrachloroethene to growth.

A microscopically pure enrichment culture of a gram-negative anaerobic bacterium, in the present article referred to as PER-K23, was isolated from an anaerobic packed-bed column in which tetrachloroethene (PCE) was reductively transformed to ethane via trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), chloroethene, and ethene. PER-K23 catalyzes the dechlorination of PCE via TCE to cis-1,2-DCE and couples this reductive dechlorination to growth. H2 and formate were the only electron donors that supported growth with PCE or TCE as an electron acceptor. The culture did not grow in the absence of PCE or TCE. Neither O2, NO3-, NO2-, SO4(2-), SO3(2-), S2O3(2-), S, nor CO2 could replace PCE or TCE as an electron acceptor with H2 as an electron donor. Also, organic electron acceptors such as acetoin, acetol, dimethyl sulfoxide, fumarate, and trimethylamine N-oxide and chlorinated ethanes, DCEs, and chloroethene were not utilized. PER-K23 was not able to grow fermentatively on any of the organic compounds tested. Transferring the culture to a rich medium revealed that a contaminant was still present. Dechlorination was optimal between pH 6.8 and 7.6 and a temperature of 25 to 35 degrees C. H2 consumption was paralleled by chloride production, PCE degradation, cis-1,2-DCE formation, and growth of PER-K23. Electron balances showed that all electrons derived from H2 or formate consumption were recovered in dechlorination products and biomass. Exponential growth could be achieved only in gently shaken cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Biodegradation, Environmental↗
PubMed1992

Enrichment and properties of an anaerobic mixed culture reductively dechlorinating 1,2,3-trichlorobenzene to 1,3-dichlorobenzene.

Hexachlorobenzene (HCB), pentachlorobenzene (QCB), all three isomers of tetrachlorobenzene (TeCB), 1,2,3-trichlorobenzene (1,2,3-TCB), and 1,2,4-TCB were reductively dechlorinated by enrichment cultures in the presence of lactate, glucose, ethanol, or isopropanol as the electron donor. The enrichment cultures originated from percolation columns filled with Rhine River sediment in which dechlorination of TCBs and dichlorobenzenes (DCBs) occurred. A stable consortium obtained by transfer on lactate as the energy and carbon source in the presence of 1,2,3-TCB dechlorinated this isomer stoichiometrically to 1,3-DCB. Dechlorinating activity could only be maintained when an electron donor was added. Lactate, ethanol, and hydrogen appeared to be the best substrates. Optimal temperature and pH for dechlorination were 30 degrees C and 7.2, respectively. The specificity of the enrichment on lactate and 1,2,3-TCB was tested after approximately 60 transfers (after 2.5 years). HCB and QCB were stoichiometrically dechlorinated to 1,3,5-TCB and minor amounts of 1,2,4-TCB. 1,3,5-TCB was the sole product formed from 1,2,3,5-TeCB, while 1,2,3,4-TeCB and 1,2,4,5-TeCB were converted to 1,2,4-TCB. 1,2,4-TCB, 1,3,5-TCB, and the three isomers of DCB were not dechlorinated during 4 weeks of incubation. For further enrichment of the 1,2,3-TCB-dechlorinating bacteria, a two-liquid-phase (hexadecane-water) system was used with hydrogen as the electron donor and 1,2,3-TCB or CO2 as the electron acceptor. Methanogens and acetogens were the major substrate-competing (H2-CO2) microorganisms in the two-liquid-phase system. Inhibition of methanogenesis by 2-bromoethanesulfonic acid did not influence dechlorination, and acetogens which were isolated from the enrichment culture did not have dechlorinating activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria, Anaerobic↗
PubMed1992

Evidence for the involvement of corrinoids and factor F430 in the reductive dechlorination of 1,2-dichloroethane by Methanosarcina barkeri.

Cobalamin and the native and diepimeric forms of factor F430 catalyzed the reductive dechlorination of 1,2-dichloroethane (1,2-DCA) to ethylene or chloroethane (CA) in a buffer with Ti(III) citrate as the electron donor. Ethylene was the major product in the cobalamin-catalyzed transformation, and the ratio of ethylene to CA formed was 25:1. Native F430 and 12,13-di-epi-F430 produced ethylene and CA in ratios of about 2:1 and 1:1, respectively. Cobalamin dechlorinated 1,2-DCA much faster than did factor F430. Dechlorination rates by all three catalysts showed a distinct pH dependence, correlated in a linear manner with the catalyst concentration and doubled with a temperature increase of 10 degrees C. Crude and boiled cell extracts of Methanosarcina barkeri also dechlorinated 1,2-DCA to ethylene and CA with Ti(III) citrate as the reductant. The catalytic components in boiled extracts were heat and oxygen stable and had low molecular masses. Fractionation of boiled extracts by a hydrophobic interaction column revealed that part of the dechlorinating components had a hydrophilic and part had a hydrophobic character. These chemical properties of the dechlorinating components and spectral analysis of boiled extracts indicated that corrinoids or factor F430 was responsible for the dechlorinations. The ratios of 3:1 to 7:1 of ethylene and CA formed by cell extracts suggested that both cofactors were concomitantly active.

Cobamides↗
PubMed1992

Methyl-coenzyme M reductase of Methanobacterium thermoautotrophicum delta H catalyzes the reductive dechlorination of 1,2-dichloroethane to ethylene and chloroethane.

Reductive dechlorination of 1,2-dichloroethane (1,2-DCA) to ethylene and chloroethane (CA) by crude cell extracts of Methanobacterium thermoautotrophicum delta H with H2 as the electron donor was stimulated by Mg-ATP. The heterodisulfide of coenzyme M (CoM) and 7-mercaptoheptanoylthreonine phosphate together with Mg-ATP partially inhibited ethylene production but stimulated CA production compared Mg-ATP alone. The pH optimum for the dechlorination was 6.8 (at 60 degrees C). Michaelis-Menten kinetics for initial product formation rates with different 1,2-DCA concentrations indicated the enzymatic character of the dechlorination. Apparent Kms for 1,2-DCA of 89 and 119 microM and Vmaxs of 34 and 20 pmol/min/mg of protein were estimated for ethylene and CA production, respectively. 3-Bromopropanesulfonate, a specific inhibitor for methyl-CoM reductase, completely inhibited dechlorination of 1,2-DCA. Purified methyl-CoM reductase, together with flavin adenine dinucleotide and a crude component A fraction which reduced the nickel of factor F430 in methyl-CoM reductase, converted 1,2-DCA to ethylene and CA with H2 as the electron donor. In this system, methyl-CoM reductase was also able to transform its own inhibitor 2-bromoethanesulfonate to ethylene.

Ethyl Chloride↗
PubMed1990

Reductive dechlorination of 1,2-dichloroethane and chloroethane by cell suspensions of methanogenic bacteria.

Concentrated cell suspensions of methanogenic bacteria reductively dechlorinated 1,2-dichloroethane via two reaction-mechanisms: a dihalo-elimination yielding ethylene and two hydrogenolysis reactions yielding chloroethane and ethane, consecutively. The transformation of chloroethane to ethane was inhibited by 1,2-dichloroethane. Stimulation of methanogenesis caused an increase in the amount of dechlorination products formed, whereas the opposite was found when methane formation was inhibited. Cells of Methanosarcina barkeri grown on H2/CO2 converted 1,2-dichloroethane and chloroethane at higher rates than acetate or methanol grown cells.

Biodegradation, Environmental↗
PubMed1984

Prostaglandin synthesis inhibitors and vasa recta erythrocyte velocities in the rat.

Vasa recta erythrocyte velocities (VRBC) in the exposed renal papilla of anesthetized water-loaded rats were determined before and 60 min after intravenous administration of a prostaglandin synthesis inhibitor (indomethacin, meclofenamate) or the inhibitor vehicle alone. The change in VRBC of ascending and descending vasa recta for the inhibitor group [-17 +/- 5% (SE)] was different from that for controls (+12 +/- 4%, P less than 0.002). Erythrocyte velocities were also determined in vasa recta of antidiuretic rats before and 30 min after administration of indomethacin or vehicle alone. Prostaglandin synthesis inhibition was again associated with a significant decrease in VRBC compared with control (-24 +/- 4% vs. +28 +/- 20%, respectively, P less than 0.025). These findings suggest that prostaglandins play a similar role in regulating blood flow in the renal medulla in water diuresis and antidiuresis.

Animals↗
PubMed1983

Direct determination of vasa recta blood flow in the rat renal papilla.

Blood flow in vasa recta capillaries of the exposed renal papilla of young antidiuretic rats (n = 18) was determined by an adaptation of the video-photometric technique of Intaglietta. The erythrocyte velocity and capillary diameter in vasa recta (n = 97) were measured at the same location by means of fluorescence video microscopy, with fluorescein-labeled bovine gamma-globulin as a plasma marker. A factor relating erythrocyte velocity to mean cross-sectional blood velocity was determined in vitro to permit the calculation of single vasa recta blood flows from the measured indices, erythrocyte velocity and capillary diameter. Mean blood flow in descending vasa recta was 8.83 +/- 0.96 (SE) nl/min, significantly greater than that in ascending vasa recta, 4.82 +/- 0.34 nl/min. The total numbers of ascending and descending vasa recta at the base of the exposed papilla were also determined. Over 1500 vasa recta were identified as ascending vasa recta or descending vasa recta in electron micrographs of three papillas. At this level in the papilla (2 mm from the tip), there were four ascending vasa recta for each descending vas rectum. From the total numbers of ascending vasa recta and descending vas rectum, single vessel blood flows were converted to total blood flow. Total blood outflow in all ascending vasa recta, 11.3 microliter/min, substantially exceeded total blood inflow in all descending vasa recta, 5.2 microliter/min. The difference between outflow and inflow (6.1 microliter/min) represents an estimate of water by the papillary microcirculation, and is more than adequate to accommodate the known rate of water reabsorption from the collecting ducts of the exposed papilla.

Animals↗
PubMed1983

Effects of glucagon, vasoactive intestinal peptide, and vasopressin on villous microcirculation and superior mesenteric artery blood flow of the rat.

The effects of the peptide hormones glucagon, vasoactive intestinal peptide, and vasopressin on the microcirculation of single jejunal villi were studied in anesthetized rats. By means of a recently developed in vivo video-microscopy technique, the red blood cell velocity (pretreatment value: 2.1 +/- 0.1 mm X s-1) and the diameter of the red blood cell column (5.5 +/- 0.2 micron) were measured in the villous arcade vessels. From these parameters, an index of blood flow was calculated in order to determine changes in response to intravenous infusions of the peptides. During the infusions of glucagon and vasopressin, simultaneous measurements were made of superior mesenteric artery blood flow and villous arcade flow. Glucagon (1 microgram X kg-1 X min-1) increased villous arcade flow markedly to 150.1 +/- 13.7% of control, while superior mesenteric artery flow remained unchanged. Vasoactive intestinal peptide (1 microgram X kg-1 X min-1) produced a dilation of the arcade vessel with a commensurate reduction of red cell velocity, leaving the flow index unaltered. Vasopressin (14.3 mU X kg-1 X min-1) was found to be a potent vasoconstrictor at the mucosal level, and since red cell velocity also decreased, villous flow was reduced substantially, paralleling a reduction of superior mesenteric artery flow. After the vasopressin infusion, a reactive hyperemia occurred in the villous arcades. No such increase in blood flow was observed in the superior mesenteric artery. From these findings, we conclude that the villous microvasculature is influenced by various hormones and, therefore, must occupy a prominent position in control of the circulation of the small intestine.

Animals↗
PubMed1977

[Microcirculation studies on rat small intestine villi in vivo].

A method of observing and studying the microcirculation in the jejunal villus of the living rat is described. It permits measurement of the velocity of plasma gaps and of the diameters of the various vessels, and is based on transillumination of the exposed mucosa. The motility of the gut is overcome by allowing the intestine to adhere to the water-immersion lens. The problems of mucous secretion are resolved by administration of N-acetyl-L-cystein. A direct arteriovenous connection between arterioles and the venous system of the villus is postulated. Plasma gap velocity is 1.78 +/- 0.62 mm/sec in the arterioles and 0.42 +/- 0.08 mm/sec in the capillaries. The measured diameter of the of the erythrocyte column in the vessels is: central artery: 9.14 +/- 1.89 micron; "arcade" arteriole part I, II and III respectively: 5.88 +/- 1.05 micron, 6.69 +/- 1.04 micron, 8.86 +/- 1.63 micron; venule: 13.58 +/- 2.67 micron; capillaries: 4.56 +/- 0.57 micron. The method also allows puncture of the villus vessels.

Acetylcysteine↗