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PubMed2005

Characterization and structural analysis of an active particulate methane monooxygenase trimer from Methylococcus capsulatus (Bath).

The oxidation of methane to methanol in methanotrophs is catalyzed by the enzyme methane monooxygenase (MMO). Two distinct forms of this enzyme exist, a soluble cytoplasmic MMO (sMMO) and a membrane-bound particulate form (pMMO). We describe here the biochemical characterization of a stable and active purified pMMO hydroxylase (pMMO-H) and report a three-dimensional (3D) structure, determined by electron microscopy and single-particle analysis at 23 A resolution. Both biochemical and structural data indicate that pMMO hydroxylase is trimeric, with each monomer unit comprised of three polypeptides of 47, 26, and 23 kDa. Comparison of the recent crystal structure [Lieberman, R. L., and Rosenzweig, A. C. (2005) Nature 434, 177] of an uncharacterized pMMO-H complex with the three-dimensional (3D) structure determined here yielded a good match between the principal features and the organization of the enzyme monomers into trimers. The data presented here advance our current understanding of particulate methane monooxygenase function by the characterization of an active form of the enzyme and the corresponding 3D structure.

Bacterial Proteins↗

PubMed2001

Measurements of methane emissions from landfills using a time correlation tracer method based on FTIR absorption spectroscopy.

Methane is an important climate gas contributing significantly to global warming. A large part of the anthropogenic emissions of methane comes from landfills. Due to the biogenic origin of these emissions and the inhomogeneous characteristics of landfills and their soil cover, these emissions show large spatial variation. Thus, development of reliable and cost-effective methods for measurements of these emissions is an important task and a challenge to the scientific community. Traditionally, field chamber methods have been used but also different area integrating methods based on downwind plume measurements. These measurements have been supported by meteorological data either directly from local measurements or by controlled release of tracer gas from the landfill providing the dispersion characteristics of the plume. In this paperwe describe a method,the Time Correlation Tracer method, combining controlled tracer gas release from the landfill with time-resolved concentration measurements downwind the landfill using FTIR absorption spectroscopy. The method has been tested and used on measurements at a landfill in southern Sweden over the past 1.5 years. The method has proven to be a usable method for measurements of total methane emission from landfills, and under favorable meteorological conditions we estimate an achievable accuracy of 15-30%. The real time analysis capability of the FTIR makes it possible to judge the success of the measurement already on site and to decide whether more measurements are necessary. The measurement strategy is relatively simple and straightforward, and one person can make a measurement from a medium sized landfill (1-4 ha) within a few days to a week depending on the meteorological situation.

Air Pollutants↗

PubMed2003

Influences of changes in multitopic tris(pyrazolyl)methane ligand topology on silver(I) supramolecular structures.

The reactions between silver tetrafluoroborate and the ligands 1,2,4,5-C(6)H(2)[CH(2)OCH(2)C(pz)(3)](4) (L1, pz = pyrazolyl ring), o-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L2), and m-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L3) yield coordination polymers of the formula (C(6)H(6)(-)(n)[CH(2)OCH(2)C(pz)(3)](n)(AgBF4)(m))( infinity ) (n = 4, m = 2, 1; n = 2, ortho substitution, m = 1, 2; meta substitution, m = 2, 3). In the solid state, L2 molecules dimerize by a pair of C-H.pi interactions, forming an arrangement that resembles the tetratopic ligand L1. In the solid-state structure of 1, each silver atom is kappa(2)-bonded to two tris(pyrazolyl)methane units from different ligands with the overall structure a polymer made up from 32-atom macrocyclic rings formed by bonding tris(pyrazolyl)methane groups from nonadjacent positions on the central arene rings to the same two silver atoms. In 2, each silver is bonded to two tris(pyrazolyl)methane units in the same kappa(2)-kappa(2) fashion as with 1, forming a polymer chain. The chains are organized into dimeric units by strong face-to-face pi-pi stacking between the central arene rings making bitopic L2 act as half of tetratopic L1. The chains in both structures are organized by weak C-H.F hydrogen bonds and pi-pi stacking interactions into very similar 3D supramolecular architectures. The structure of 3 contains three types of silvers with the overall 3D supramolecular sinusoidal structure comprised of 32-atom macrocycles. Infrared studies confirm the importance of the noncovalent interactions. Calculations at the DFT (B3LYP/6-31G) level of theory have been carried out on L2 and also support C-H.pi interactions. Electrospray mass spectral data collected from acetone or acetonitrile show the presence of aggregated species such as [(L)Ag(2)(BF(4))](+) and [(L)Ag(2)](2+), despite the fact that (1)H NMR spectra of all compounds show that acetonitrile completely displaces the ligand whereas acetone does not.

Crystallography, X-Ray↗

PubMed2006

Origin of the attraction in aliphatic C-H/pi interactions: infrared spectroscopic and theoretical characterization of gas-phase clusters of aromatics with methane.

An attractive intermolecular interaction between an aliphatic C-H bond and a pi-electron system (C-H/pi interaction) was characterized on the basis of infrared spectroscopy and high level ab initio calculations. Infrared spectroscopy was applied to several isolated methane clusters with benzene, toluene, p-xylene, mesitylene, and naphthalene in the gas phase, and the spectral changes of the C-H stretch bands in the methane moiety upon the cluster formation were observed. In the theoretical approach, interaction energies of the clusters were evaluated by high-level ab initio calculations. The forbidden symmetric C-H stretch transition weakly appeared in the IR spectra of the clusters, and it confirmed the small deformation of the methane moiety from the T(d)() symmetry, which was predicted by the ab initio calculations. On the other hand, the degenerated asymmetric C-H stretch band showed complicated splitting, which is qualitatively interpreted by a hindered rotor model. Low-frequency shifts upon the cluster formation were seen in the symmetric C-H stretch frequency, though the magnitude of the shifts was extremely small and no clear correlation with the interaction energy was found. On the other hand, the size of the calculated interaction energy well correlates with the polarizability of aromatics. The S(1)-S(0) electronic transition of the aromatic moiety was also observed, and it showed low-frequency shifts upon cluster formation. These results support the dominance of the dispersion interaction over the electrostatic and charge-transfer terms in the aliphatic C-H/pi interaction.

Benzene↗

PubMed1997

Reliability and reproducibility of breath hydrogen and methane in male diabetic subjects.

We studied the variability and reliability of breath hydrogen and methane as well as the alterations in intestinal gas profile in response to lactulose ingestion in 13 asymptomatic male patients with diabetes mellitus (DM). Seventeen healthy subjects served as controls. The prevalence of methane producers was 33% in DM and 45% among control subjects (P = NS). The prevalence of nonhydrogen producers was 7.7% and 5.9%, respectively. The coefficient for interday variation of H2 was 72.6 +/- 9.8% in DM and 49.7 +/- 9.8% in controls (P < 0.05). Similarly, the coefficient for interday variation of CH4 was 94.3 +/- 18.8 and 69.4 +/- 16.8% respectively (P = NS). The reproducibility of basal H2 and CH4 among diabetics as assessed by r1 (measure of reliability) was poorer among diabetics when breath analysis was performed on different days (P < 0.001). There was no significant difference between diabetics and controls with respect to basal or peak or area under the curve for H2 and CH4 in response to lactulose. We conclude that there is poor reproducibility of fasting breath gas levels among asymptomatic male subjects with diabetes. In addition, DM is not associated with alterations in hydrogen- or methane-producing potential.

Adult↗

PubMed1992

Possible methane-induced polar warming in the early Eocene.

Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of Earth without noticeably warming the tropics remains unresolved; increased amounts of greenhouse gases would be expected to warm all latitudes equally. Oceanic heat transport has been postulated as a mechanism for heating high latitudes, but it is difficult to explain the dynamics that would achieve this. Here we consider estimates of Eocene wetland areas and suggest that the flux of methane, an important greenhouse gas, may have been substantially greater during the Eocene than at present. Elevated methane concentrations would have enhanced early Eocene global warming, and also might specifically have prevented severe winter cooling of polar regions because of the potential of atmospheric methane to promote the formation of optically thick, polar stratospheric ice clouds.

Atmosphere↗

PubMed2001

Detection of chlorinated methanes by tin oxide gas sensors.

Tin oxide thin films prepared by thermal oxidation of Sn films were used for the detection of chlorinated methanes (CH2Cl2, CHCl3 and CCl4). This resulted in better chemical selectivity, sensitivity, response speed and detection limit than seen with previous detectors. The temperature dependence of the sensing of 1% CCl4 gas was studied and the best sensing behavior was observed at 300 degrees C. The films showed different chemical selectivity in both speed and direction of sensing response to each gas and were stable for more than 3 weeks under operating conditions. The films showed rapid gas sensing (<40 s to reach 90% of full response) and low detection limits (< 4 ppm CCl4). The role of oxygen in the detection of chlorinated methanes and in resistance changes without chlorinated methanes was also studied. The changes at the surface of the film after gas sensing were examined using scanning electron microscopy with energy-dispersive X-ray spectrometry.

Chlorofluorocarbons, Methane↗

PubMed1977

The soluble methane mono-oxygenase of Methylococcus capsulatus (Bath). Its ability to oxygenate n-alkanes, n-alkenes, ethers, and alicyclic, aromatic and heterocyclic compounds.

1. Methane mono-oxygenase of Methylococcus capsulatus (Bath) catalyses the oxidation of various substituted methane derivatives including methanol. 2. It is a very non-specific oxygenase and, in some of its catalytic properties, apparently resembles the analogous enzyme from Methylomonas methanica but differs from those found in Methylosinus trichosporium and Methylomonas albus. 3. CO is oxidized to CO2. 4. C1-C8 n-alkanes are hydroxylated, yielding mixtures of the corresponding 1- and 2-alcohols; no 3- or 4-alcohols are formed. 5. Terminal alkenes yield the corresponding 1,2-epoxides. cis- or trans-but-2-ene are each oxidized to a mixture of 2,3-epoxybutane and but-2-en-1-ol with retention of the cis or trans configuration in both products; 2-butanone is also formed from cis-but-2-ene only. 6. Dimethyl ether is oxidized. Diethyl ether undergoes sub-terminal oxidation, yielding ethanol and ethanal in equimolar amounts. 7. Methane mono-oxygenase also hydroxylates cyclic alkanes and aromatic compounds. However, styrene yields only styrene epoxide and pyridine yields only pyridine N-oxide. 8. Of those compounds tested, only NADPH can replace NADH as electron donor.

Alkanes↗

PubMed1984

Methane synthesis by membrane vesicles and a cytoplasmic cofactor isolated from Methanobacterium thermoautotrophicum.

Methanobacterium thermoautotrophicum when grown on ordinary culture medium has a tough cell wall which is lysozyme-resistant and difficult to disrupt by physical means. The cell wall, however, can be weakened by the addition of D-sorbitol to the growth medium and the organisms form protoplasts after lysozyme addition. This technique allowed the isolation of two types of intracellular small vesicles: (a) isolated by disruption of the total cell population (lysozyme-sensitive and lysozyme-resistant cells) by ultrafrequency sound and (b) isolated by osmotic lysis of protoplasts. For the first time, a small vesicle fraction isolated as in (a) was capable of synthesizing methane from CO2 and H2 without cytoplasm. There was, however, an absolute requirement for a small, heat-stable, oxygen-sensitive cofactor which was isolated from the cytoplasm. Methane synthesis with this vesicle fraction was inhibited by the detergent deoxycholate, and by the protonophores 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone. Mg2+-ATPase appeared to be located on the outer or cytoplasmic surface of the small vesicle fraction isolated as in (b). The results were consistent with a previously made suggestion [Sauer, Erfle & Mahadevan (1981) J. Biol. Chem. 256, 9843-9848] that the interior of the small intracellular vesicles becomes acid during methane synthesis.

Cell Fractionation↗

PubMed2003

Cofactor-independent oxygenation reactions catalyzed by soluble methane monooxygenase at the surface of a modified gold electrode.

Soluble methane monooxygenase (sMMO) is a three-component enzyme that catalyses dioxygen- and NAD(P)H-dependent oxygenation of methane and numerous other substrates. Oxygenation occurs at the binuclear iron active centre in the hydroxylase component (MMOH), to which electrons are passed from NAD(P)H via the reductase component (MMOR), along a pathway that is facilitated and controlled by the third component, protein B (MMOB). We previously demonstrated that electrons could be passed to MMOH from a hexapeptide-modified gold electrode and thus cyclic voltammetry could be used to measure the redox potentials of the MMOH active site. Here we have shown that the reduction current is enhanced by the presence of catalase or if the reaction is performed in a flow-cell, probably because oxygen is reduced to hydrogen peroxide, by MMOH at the electrode surface and the hydrogen peroxide then inactivates the enzyme unless removed by catalase or a continuous flow of solution. Hydrogen peroxide production appears to be inhibited by MMOB, suggesting that MMOB is controlling the flow of electrons to MMOH as it does in the presence of MMOR and NAD(P)H. Most importantly, in the presence of MMOB and catalase, the electrode-associated MMOH oxygenates acetonitrile to cyanoaldehyde and methane to methanol. Thus the electochemically driven sMMO showed the same catalytic activity and regulation by MMOB as the natural NAD(P)H-driven reaction and may have the potential for development into an economic, NAD(P)H-independent oxygenation catalyst. The significance of the production of hydrogen peroxide, which is not usually observed with the NAD(P)H-driven system, is also discussed.

Acetonitriles↗

PubMed2001

Bacterial populations occuring in a trichloroethylene-contaminated aquifer during methane injection.

Soil core samples were obtained from a trichloroethylene (TCE)-contaminated aquifer before and after the start of methane biostimulation. DNA was extracted directly from the soil samples, and denaturing gradient gel electrophoresis (DGGE) was used to analyse bacterial 16S ribosomal DNA fragments that were PCR amplified from these DNA samples. This analysis consistently detected two phylotypes in the methane-injected samples. These phylotypes were closely related to Methylobacter and Methylomonas, both belonging to type I methanotrophs. A competitive DGGE analysis using Methylosinus trichosporium OB3b cells as an internal quantitative standard showed that these populations accounted for 10(8)-10(9) cells g(-1) soil. These results showed that type I methanotrophs formed a significant proportion of the bacterial community during methane biostimulation. The implications of this finding for TCE bioremediation were discussed.

Biodegradation, Environmental↗

PubMed2005

Search for memory effects in methane hydrate: structure of water before hydrate formation and after hydrate decomposition.

Neutron diffraction with HD isotope substitution has been used to study the formation and decomposition of the methane clathrate hydrate. Using this atomistic technique coupled with simultaneous gas consumption measurements, we have successfully tracked the formation of the sI methane hydrate from a water/gas mixture and then the subsequent decomposition of the hydrate from initiation to completion. These studies demonstrate that the application of neutron diffraction with simultaneous gas consumption measurements provides a powerful method for studying the clathrate hydrate crystal growth and decomposition. We have also used neutron diffraction to examine the water structure before the hydrate growth and after the hydrate decomposition. From the neutron-scattering curves and the empirical potential structure refinement analysis of the data, we find that there is no significant difference between the structure of water before the hydrate formation and the structure of water after the hydrate decomposition. Nor is there any significant change to the methane hydration shell. These results are discussed in the context of widely held views on the existence of memory effects after the hydrate decomposition.

Chemistry, Physical↗

PubMed2004

Sulfur pollution suppression of the wetland methane source in the 20th and 21st centuries.

Natural wetlands form the largest source of methane (CH(4)) to the atmosphere. Emission of this powerful greenhouse gas from wetlands is known to depend on climate, with increasing temperature and rainfall both expected to increase methane emissions. This study, combining our field and controlled environment manipulation studies in Europe and North America, reveals an additional control: an emergent pattern of increasing suppression of methane (CH(4)) emission from peatlands with increasing sulfate (SO(4)(2-)-S) deposition, within the range of global acid deposition. We apply a model of this relationship to demonstrate the potential effect of changes in global sulfate deposition from 1960 to 2080 on both northern peatland and global wetland CH(4) emissions. We estimate that sulfur pollution may currently counteract climate-induced growth in the wetland source, reducing CH(4) emissions by approximately 15 Tg or 8% smaller than it would be in the absence of global acid deposition. Our findings suggest that by 2030 sulfur pollution may be sufficient to reduce CH(4) emissions by 26 Tg or 15% of the total wetland source, a proportion as large as other components of the CH(4) budget that have until now received far greater attention. We conclude that documented increases in atmospheric CH(4) concentration since the late 19th century are likely due to factors other than the global warming of wetlands.

Acid Rain↗

PubMed1997

Concentrations and emission rates of aerial ammonia, nitrous oxide, methane, carbon dioxide, dust and endotoxin in UK broiler and layer houses.

1. A survey of the concentration and emission rates of aerial ammonia, nitrous oxide, methane, carbon dioxide, dust and endotoxin was undertaken in 4 examples each of typical UK broiler, cage and perchery houses over 24 h during winter and summer. 2. Overall the air quality within the poultry houses was unsatisfactory as judged by the dual criteria of farmer health and bird performance. 3. Mean concentrations of ammonia ranged from 12.3 to 24.2 ppm while concentrations of methane and nitrous oxide were close to ambient levels. Mass concentrations of aerial dust ranged from 2 to 10 mg/m3 and 0.3 to 1.2 mg/m3 for inspirable and respirable fractions respectively, while endotoxin concentration was typically about 0.1 microgram/m3 (inspirable fraction). 4. Emission rates of gaseous ammonia were rapid (9.2 g (NH3)/h per 500 kg live body weight) and uniform across the three types of building, while emissions of methane and nitrous oxide were slow. Rates of dust emission ranged from 0.86 to 8.24 g/h per 500 kg live body weight in the inspirable size fraction.

Air Pollution, Indoor↗

PubMed2005

Transformation of chlorinated methanes by zero-valent aluminum coupled with Pd/Al2O3.

The transformation of chlorinated methanes by zero-valent aluminum under various pH conditions has been examined in the presence and absence of Pd/Al2O3. In the absence of Pd/Al2O3, carbon tetrachloride was primarily transferred to chloroform (65%) and dichloromethane (15.3%) at pH 2.5 while little of the hydrodehalogenation intermediates (approximately 5%) was found at pH 10.8. This indicates that carbon tetrachloride undergoes hydrodehalogenation at low pH but not at high pH. The low production of hydrodehalogenation intermediates at high pH could be attributed to the base-catalyzed hydrolysis of carbon tetrachloride resulting in the formation of products that can not be detected by the provided analytic methods. In the presence of Pd/Al2O3, degradation rates were increased by a factor of 10-43 compared to the system without Pd/Al2O3, suggesting Pd/Al2O3, serves as a catalyst. Further, complete degradation of carbon tetrachloride by zero-valent aluminum with Pd/Al2O3 led directly to methane (86.4%) without formation and accumulation of dichloromethane at pH 9.0. The direct transformation of carbon tetrachloride to methane can be rationalized by the catalytic hydrodehalogenation occurring at the palladium surface. The study indicates aluminum coupled with Pd/Al2O3 is an environmentally-friendly technology for treatment of chlorinated organic contaminants.

Aluminum Oxide↗

PubMed2006

Impact of water table depth on forest soil methane turnover in laboratory soil cores deduced from natural abundance and tracer 13C stable isotope experiments.

We investigated turnover of methane (CH4) in soils from a poorly drained UK forest. In situ, this forest exhibited a negligible soil-atmosphere CH4 flux, whereas adjacent grassland plots were sources of CH4. We hypothesised that the forest plots exhibited reduced anaerobic CH4 production through water-table draw down. Consequently, we exposed soil cores from under oak to high and low water-table conditions in the laboratory. Methane fluxes increased significantly in the high water-table (1925+/-1702 mug CH4 m(-2) h(-1)) compared to the low one (-3.5+/-6.8 microg CH4 m(-2) h(-1)). Natural abundance delta13C values of CH4 showed a strong depletion in high water-table cores (-56.7+/-2.9 per thousand) compared to methane in ambient air (-46.0 per thousand) indicative of methanogenic processes. The delta13C values of CH4 from low water-table cores (delta13C-46.8+/-0.2 per thousand) was similar to ambient air and suggested little alteration of headspace CH4 by the soil microbial community. In order to assess the CH4 oxidizing activity of the two treatments conclusively, a 13CH4 spike was added to the cores and 13CO2 production was measured as the by-product of CH4 oxidation. 13CH4 oxidation rates were 57.5 (+/-12.7) and 0.5 (+/-0.1) microg CH4 m(-2) h(-1) for high and low water-tables, respectively. These data show that the lower water-table hydrology treatment impacted methanogenic processes without stimulating methanotrophy.

Carbon Isotopes↗

PubMed1998

The effect of porcine bile acids on methane production by rumen contents in vitro.

Hindgut fermentation differs from rumen fermentation by a lower methane production and the presence of reductive acetogenesis. Bile acids which are lost into the lower digestive tract may have a promoting effect on reductive acetogenesis in the hindgut. In this experiment it was investigated if bile acids induce reductive acetogenesis in rumen fermentation in vitro. Rumen contents from a fistulated cow were incubated in vitro with ground hay and increasing amounts of porcine bile acids or bile acid salts. Bile acids inhibited methane production up to 70% of the control incubation. The concomitant increase in propionate production compensated for the lower methane production so that the 2H-recoveries were in a normal range between 79-92%. Therefore the occurrence of reductive acetogenesis could be excluded. It is concluded, that bile acids are a controlling factor in caecal methanogenesis.

Animals↗

PubMed2004

Anaerobic digestion and methane generation potential of rose residue in batch reactors.

In the study, anaerobic digestion of residues from rose oil industry was investigated by using a laboratory scale completely mixed batch reactor in volume of 10 L and 4 small reactors in volume of 400 mL. Ten liters reactor isolated with a water jacket and 0.4 L reactors settled into a water bath were operated at 35 +/- 1 degrees C. The study supplies biochemical methane potential of hydrolyzed and original residues. Experimental results showed that hydrolyzed rose residue produced a bit more methane than original residue. Methane production results were analyzed with first-order and Chen&Hashimoto's models, and Chen&-Hashimoto's model was found to be more suitable than first-order kinetic model.

Bacteria, Anaerobic↗