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1.
Conversion of methanol to CH4 has a large isotope effect so that a small contribution of methanol-dependent CH4 production may decrease the 13CH4 of total CH4 production. Therefore, we investigated the role of methanol for CH4 production. Methanol was not detectable above 10 M in anoxic methanogenic rice field soil. Nevertheless, addition of 13C-labeled methanol (99% enriched) resulted in immediate accumulation of 13CH4. Addition of 0.1 M 13C-methanol resulted in increase of the 13CH4 from –47 to –6 within 2 h, followed by a slow decrease. Addition of 1 M 13C-methanol increased 13CH4 to +500 within 4 h, whereas 10 M increased 13CH4 to +2500 and continued to increase. These results indicate that the methanol concentrations in situ, which diluted the 13C-methanol added, were 0.1 M and that the turnover of methanol contributed only about 2% to total CH4 production at 0.1 M. However, contribution increased up to 5 and 17% when 1 and 10 M methanol were added, respectively. Anoxic rice soil that was incubated at different temperatures between 10 and 37 °C exhibited maximally 2–6% methanol-dependent methanogenesis about 1–2 h after addition of 1 M 13C-methanol. Only at 50 °C, contribution of methanol to CH4 production reached a maximum of 10%. After longer (7–10 h) incubation, however, contribution generally was only 2–4%. Methanol accumulated in the soil when CH4 production was inhibited by chloroform. However, the accumulated methanol accounted for only up to 0.7 and 1.2% of total CH4 production at 37 and 50 °C, respectively. Collectively, our results show that methanol-dependent methanogenesis was operating in anoxic rice field soil but contributed only marginally to total CH4 production and the isotope effect observed at both low and high temperature.  相似文献   

2.
Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10-2 mol l–1, gibberellic acid (GA3) 3.10-2 mol l–1, and 6-benzylaminopurine (BA) 2 mol l–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l–1, GA3 14 mol l–1, and kinetin 5 mol l–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l–1 and BA 10 mol l–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA3 gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy  相似文献   

3.
Methane formation from acetate in cell suspensions of Methanosarcina barkeri was inhibited by low concentrations (5 M) of propyl iodide. Inhibition was abolished by short exposure of the suspension to light which strongly indicates that a corrinoid enzyme is involved in methanogenesis from acetate. Propyl iodide (5M) had no effect on the exchange reaction between the carboxyl group of acetate and 14CO2, and on methane formation from methanol, from H2 and methanol, or from H2 and CO2. These findings indicate that the proposed corrinoid enzyme has a role in methyl group transfer to coenzyme M after C-C cleavage of acetate.Dedicated to Professor N. Pfennig on the occasion of his 60th birthday  相似文献   

4.
Single-chain Fv molecules in monovalent (sFv) and divalent [(sFv')2] forms exhibit highly specific tumor targeting in mice as a result of their small size and rapid systemic clearance. As a consequence, there is a rapid reversal of the sFv blood/tumor gradient, resulting in diminished retention of sFv species in tumors. In this report we investigate two distinct strategies, dose escalation and repetitive intravenous (i.v.) dosing, aiming to increase the absolute selective retention of radiolabeled anti-c-erbB-2125I-741F8 (sFv')2 in c-erbB-2-overexpressing SK-OV-3 tumors in mice with severe combined immunodeficiency (SCID). A doseescalation strategy was applied to single i.v. injections of125I-741F8 (sFv')2. Doses from 50 g to 1000 g were administered without a significant decrease in tumor targeting or specificity. High doses resulted in large increases in the absolute retention of125I-741F8 (sFv')2. For example, raising the administered dose from 50 g to 1000 g increased the tumor retention 24 h after injection from 0.46 g/g to 9.5 g/g, and resulted in a net increase of greater than 9 /g. Over the same dose range, the liver retention rose from 0.06 g/g to 1 g/g, and resulted in a net increase of less than 1 g/g. The retention of 9.5 g/g in tumor 24 h fllowing the 1000-g dose of (sFv')2 was comparable to that seen 24 h after a 50-g dose of125I-741F8 IgG, indicating that the use of large doses of (sFv')2 may partially offset their rapid clearance. When two doses were administered by i.v. injection 24 h apart, the specificity of delivery to tumor observed after the first dose was maintained following the second injection. Tumor retention of125I-741F8 (sFv')2 was 0.32 g/g at 24 h and 0.22 g/g at 48 h following a single injection of 20 g/g, while 0.04 g/ml and 0.03 g/ml were retained in blood at the same assay times. After a second 20-g injection at the 24-h assay time, tumor retention increased to 0.49 g/g, and blood retention was 0.06 g/ml, at the 48-h point. These results suggest that multiple high-dose administrations of radiolabeled 741F8 (sFv')2 may lead to the selective tumor localization of therapeutic radiation doses.Supported by National Cancer Institute (NCI) National Cooperative Drug Discovery Group grant U01 CA51880, CA06927, an appropriation from the Commonwealth of Pennsylvania, and the Bernard A. and Rebecca S. Bernard Foundation  相似文献   

5.
Rusanov  I. I.  Lein  A. Yu.  Pimenov  N. V.  Yusupov  S. K.  Ivanov  M. V. 《Microbiology》2002,71(4):479-487
Seasonal investigations of methane distribution and rates of its oxidation and generation in the water column and sediments of the Black Sea northwestern shelf were carried out within the framework of the interdisciplinary projects European River–Ocean Systems (EROS-2000, EROS-21) and Biogenic Gases Exchange in the Black Sea (BigBlack) in August 1995, May 1997, and December 1999. Experiments that involved the addition of 14CH3COONa and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 559 mol/(m2 day)) were found in coastal sediments in summer time. In winter and spring, methane production in the same sediments did not exceed 3.6–4.2 mol/(m2 day). The 13C values of methane ranged from –70.7 to –81.8, demonstrating its microbial origin and contradicting the concept of the migration of methane from cold seeps or from the oil fields located on the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of the methane (from 6.8 to 320 mol/(m2 day)) arrives in the atmosphere.  相似文献   

6.
The potentials for sequential reduction of inorganic electron acceptors and production of methane have been examined in sixteen rice soils obtained from China, the Philippines, and Italy. Methane, CO2, Fe(II), NO 3 - , SO 4 2 , pH, Eh, H2 and acetate were monitored during anaerobic incubation at 30 °C for 120 days. Based on the accumulation patterns of CO2 and CH4, the reduction process was divided into three distinct phases: (1) an initial reduction phase during which most of the inorganic electron acceptors were depleted and CO2 production was at its maximum, (2) a methanogenic phase during which CH4 production was initiated and reached its highest rate, and (3) a steady state phase with constant production rates of CH4 and CO2. The reduction phases lasted for 19 to 75 days with maximum CO2 production of 2.3 to 10.9 mol d-1 g-1 dry soil. Methane production started after 2 to 87 days and became constant after about 38--68 days (one soil >120 days). The maximum CH4 production rates ranged between 0.01 and 3.08 mol d-1 g-1. During steady state the constant CH4 and CO2 production rates varied from 0.07 to 0.30 mol d-1 g-1 and 0.02 and 0.28 mol d-1 g-1, respectively. Within the 120 d of anaerobic incubation only 6--17% of the total soil organic carbon was released into the gas phase. The gaseous carbon released consisted of 61--100% CO2, <0.1--35% CH4, and <5% nonmethane hydrocarbons. Associated with the reduction of available Fe(III) most of the CO2 was produced during the reduction phase. The electron transfer was balanced between total CO2 produced and both CH4 formed and Fe(III), sulfate and nitrate reduced. Maximum CH4 production rate (r = 0.891) and total CH4 produced (r = 0.775) correlated best with the ratio of soil nitrogen to electron acceptors. Total nitrogen content was a better indicator for available organic substrates than the total organic carbon content. The redox potential was not a good predictor of potential CH4 production. These observations indicate that the availability of degradable organic substrates mainly controls the CH4 production in the absence of inorganic electron acceptors.  相似文献   

7.
The light utilization efficiency and relative photon requirement of photosynthesis in pulsed and continuous light from light emitting diodes (LEDs) has been measured. First, we chacterized the photon requirement of photosynthesis from light of LEDs that differ in spectral quality. A photon requirement of 10.3±0.4 was measured using light from a 658 nm peak wavelength (22 nm half band width) LED over the range of 0–50 mol photons m–2 s–1 in 2 kPa O2 in leaves of tomato (Lycopersicon esculentum Mill., cv. VF36). Because the conversion of electrical power to photons increased with wavelength, LED lamps with peak photon output of 668 nm were most efficient for converting electricity to photosynthetically fixed carbon. The effect of pulsed irradiation on photosynthesis was then measured. When all of the light to make the equivalent of 50 mol photons m–2 s–1 was provided during 1.5 s pulses of 5000 mol photons m–2 s–1 followed by 148.5 s dark periods, photosynthesis was the same as in continuous 50 mol photons m–2 s–1. When the pulse light and dark periods were lengthened to 200 s and 19.8 ms, respectively, photosynthesis was reduced, although the averaged photon flux density was unchanged. Under these conditions, the light pulses delivered 1017 photons m–2, which we calculate to be equivalent to the capacitance of PS I or PS II. Data support the theory that photons in pulses of 100 s or shorter are absorbed and stored in the reaction centers to be used in electron transport during the dark period. When light/dark pulses were lengthened to 2 ms light and 198 ms dark, net photosynthesis was reduced to half of that measured in continuous light. Pigments of the xanthophyll cycle were not affected by any of these pulsed light treatments even though zeaxanthin formation occurred when leaves were forced to dissipate an equal amount of continuous light.Abbreviations CWF cool white fluorescent - EPS xanthophyll epoxidation state - LED light emitting diode - LUE light utilization efficiency - PFD photon flux density - PR photon requirement (for CO2 fixation) - PS II primary donor in Photosystem II - RPR relative photon requirement  相似文献   

8.
Dagurova  O. P.  Namsaraev  B. B.  Kozyreva  L. P.  Zemskaya  T. I.  Dulov  L. E. 《Microbiology》2004,73(2):202-210
The activity of methanogenic and methanotrophic bacteria was evaluated in bottom sediments of Lake Baikal. Methane concentration in Baikal bottom sediments varied from 0.0053 to 81.7 ml/dm3. Bacterial methane was produced at rates of 0.0004–534.7 l CH4/(dm3 day) and oxidized at rates of 0.005–1180 l CH4/(dm3 day). Peak methane production and oxidation were observed in Frolikha Bay near a methane vent. Methane was emitted into water at rates of 49.2–4340 l CH4/(m2 day). Rates of bacterial methane oxidation in near-bottom water layers ranged from 0.002 to 1.78 l/(l day). Methanogens and methanotrophs were found to play an important role in the carbon cycle through all layers of sediments, particularly in the areas of methane vent and gas-hydrate occurrence.  相似文献   

9.
A method has been developed for the preparation of zoospores from Phytophthora palmivora which allows the ionic composition of the suspension medium to be closely controlled. Sub-micromolar concentrations of calcium ions have been shown to play a key role in maintaining the zoospore state and in the transition to the cyst stage. Restriction of free Ca2+ to between 0.2 and 1 M resulted in zoospores which could be maintained for several hours before they finally encysted and germinated. When exposed to citrus-pectin, or 3 mM SrCl2, or to vigorous shaking, these zoospores underwent rapid synchronous encystment. At free Ca2+ concentrations below 0.1 M, zoospores lysed slowly. If exposed to inducers of encystment before lysis had occurred, the zoospores failed to respond to pectin or to vigorous shaking. However, they did differentiate in response to SrCl2 addition. Provided the free Ca2+ was maintained between 0.02 and 0.2 M, zoospores survived gentle centrifugation, a procedure which previously had resulted in encystment.Abbreviations IM (ion-mix) release medium containing 100 M KCl, 10 M CaCl2, and 10 M MgCl2  相似文献   

10.
The O2 dependence of net H+ efflux of maize coleoptiles has been investigated. Below 100 M O2, H+ efflux in young (1 cm long) coleoptiles is markedly decreased while old (7 cm long) coleoptiles show a decline only at 10 M O2. Old coleoptiles show the same decrease in net H+ efflux as young ones if treated with fusicoccin. The ratio of alteration of CO2 production to the change in net proton efflux is about 1:1 at 40–80 M O2 but not at 10 M O2. An influx can be observed at 10 M O2 in young as well as in old coleoptiles if the H+ concentration is held at values below pH 6.5. Lower O2 concentrations lead to an increase of net H+ efflux, which might be caused by leaching of organic acids resulting from anaerobic processes, but CO2 production is not significantly changed at these values. It is proposed that more than one system is responsible for proton translocation across the plasmalemma. One of the systems has a high sensitivity to reduced O2 concentration which is within the same range as the high Km of the alternative path.Abbreviation FC fusicoccin  相似文献   

11.
Methanobacterium thermoautotrophicum was grown on a mineral salts medium in a fermenter gassed with H2 and CO2, which were the sole carbon and energy sources. Under the conditions used the bacterium grew exponentially. The dependence of the growth rate () on the concentration of H2 and CO2 in the incoming gas and the dependence of the growth yield ( ) on the growth rate were determined at pH 7 (the pH optimum) and 65° C (the temperature optimum).The curves relating growth rate to the H2 and CO2 concentration were hyperbolic. From reciprocal plots apparent K s values for H2 and CO2 and max were obtained: app. = 20%; app. = 11%; = 0.69 h-1; t (max)=1 h. was 1.6 g mol-1 and almost independent of the growth rate, when the rate of methane formation was not limited by the supply of either H2 or CO2. The yield increased to near 3 g mol-1 when H2 or CO2 were limiting. These findings indicate that methane formation and growth are less tightly coupled at high concentrations of H2 or CO2 in the medium than at low concentrations. The physiological significance of these findings is discussed. K s: H2 and CO2 concentration supporting 0.5 max; max: specific growth rate at infinite substrate concentration; Y s:growth yield (g dry weight/mol substrate); t : doubling time  相似文献   

12.
Desulfovibrio vulgaris strain Madison outcompetedMethanobacterium strain ivanov for hydrogen when sulfate was in excess because of higher cell yield and growth rate and a greater affinity for hydrogen as a consequence of a lower Km and higher Vmax for in vivo hydrogenase activity.Desulfovibrio vulgaris displayed a growth yield of 1.1 g/mol H2, a Km for tritium exchange of 4 M, and a specific in vivo hydrogenase activity of 2.17 DPM3H2O×103/g cell protein/h; whereasMethanobacterium strain ivanov had a yield of 0.6 g/mol H2, a Km for tritium exchange of 14 M, and a specific in vivo hydrogenase activity of 0.38 DPM3H2O×103/g cell protein/h. Under these physiological conditions, the Gibbs free-energy change associated with methanogenesis and sulfidogenesis from H2 was calculated to be-47.4 kJ/mol and-62.9 kJ/mol, respectively. When sulfidogenesis was limited by sulfate concentration, the methanogen was able to successfully compete with the sulfidogen for hydrogen. Competition between methanogens and sulfidogens for hydrogen is explained in terms of thermodynamic, kinetic, and other important considerations not discussed in the previous literature.  相似文献   

13.
Husen  Jia  Dequan  Li 《Photosynthetica》2002,40(1):139-144
The responses to irradiance of photosynthetic CO2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd). Net photosynthetic rate (P N) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (mol m-2 s-1, while the PS2 non-cyclic electron transport (P-rate) showed a maximum at PPFD 800 mol m-2 s-1. With PPFD increasing, either leaf potential photosynthetic CO2 assimilation activity (Fd/Fs) and PS2 maximal photochemical activity (Fv/Fm) decreased or the ratio of the inactive PS2 reaction centres (RC) [(Fi – Fo)/(Fm – Fo)] and the slow relaxing non-photochemical Chl fluorescence quenching (qs) increased from PPFD 1 200 mol m-2 s-1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(Fs – Fo)/Fm – Fo)], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (qf and qm) increased remarkably from PPFD 900 (mol m-2 s-1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 mol m-2 s-1 and photoinhibition occurred above PPFD 900 mol m-2 s-1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 mol m-2 s-1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 mol m-2 s-1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter P N and the Chl fluorescence parameter Fv/Fm as a definition of saturation irradiance and photoinhibition of plant leaves.  相似文献   

14.
Feeding in the rotifer Brachionus calyciflorus   总被引:7,自引:0,他引:7  
Summary The laboratory feeding behavior of Brachionus calyciflorus varies depending upon the type of food cell available in suspension. When feeding on the yeast Rhodotorula glutinis, rotifers show a continuous increase in ingestion with increased cell density between 0.01 and 1000 g dry weight ml-1. Effective clearance rates drop from ca. 50 l animal-1 h-1 to less than 0.5 l animal-1 h-1 over this food density range. When feeding on Englena gracilis, B. calyciflorus ingestion rates are constant between 1.0 and 100 g ml-1 of available food, averaging close to 25 ng animal-1 h-1. The decrease in clearance rate is more striking than with R. glutinis, dropping from 45 l animal-1 h-1 at 0.1 g ml-1 to 0.13 l animal-1 h-1 at 100 g ml-1. Differences between the patterns obtained with the two food types indicate fundamental dissimilarities in the feeding behavior of this rotifer species when presented with these different foods.  相似文献   

15.
Intensity of 2 s delayed fluorescence (DF) as a function of steady-state actinic light intensity was investigated in pea chloroplasts in the presence of 10 M DCMU. The light saturation curve of DF was approximated by a sum of two hyperbolic components which differ by an order of magnitude in the half-saturating incident light intensity. The relative contribution of the amplitudes of the components was practically independent of cation (Na+ and Mg2+) concentration and a short-term heating of the chloroplasts at 45°C. The component saturating at low incident light intensity was selectively suppressed by 100 M DCMU or by 1 mol g-1 Chl oleic acid. DF intensity following excitation by a single saturating 15 s flash was equal to the intensity of the component saturating at a low incident light intensity. Upon flash excitation, the maximum steady-state DF level was found to be attained only after a series of saturating flashes. It is concluded that the two components of the DF light saturation curves are related to PS II centres heterogeneity in quantum yield of stabilization of the reduced primary quinone acceptor.Abbreviations DF Delayed fluorescence - L1- and L2-components DF components saturating at low and high incident light intensity, respectively - I incident light intensity - L DF intensity - P680 reaction centre chlorophyll of PS II - QA and QB primary and secondary quinone acceptors of PS II, respectively  相似文献   

16.
Summary A study has been made of the mineral requirements ofBacillus thuringiensis subsp.israelensis for production of the mosquitocide delta endotoxin. The optimum concentrations of K2HOP4, MgSO4.7H2O and CaCO3 for toxin production are 1g/l, 0.3g/l and 1g/l respectively while the elements Fe, Mn, Cu are required at levels of 2 g/ml, 5 g/ml and 0.25 g/ml respectively.  相似文献   

17.
An assay is described that allows the direct measurement of the enzyme activity catalyzing the transfer of the methyl group from N 5-methyltetrahydromethanopterin (CH3–H4MPT) to coenzyme M (H–S–CoM) in methanogenic archaebacteria. With this method the topology, the partial purification, and the catalytic properties of the methyltransferase in methanol- and acetate-grown Methanosarcina barkeri and in H2/CO2-grown Methanobacterium thermoautotrophicum were studied. The enzyme activity was found to be associated almost completely with the membrane fraction and to require detergents for solubilization. The transferase activity in methanol-grown M. barkeri was studied in detail. The membrane fraction exhibited a specific activity of CH3–S–CoM formation from CH3–H4MPT (apparent K m=50 M) and H–S–CoM (apparent K m=250 M) of approximately 0.6 mol·min-1·mg protein-1. For activity the presence of Ti(III) citrate (apparent K m=15 M) and of ATP (apparent K m=30 M) were required in catalytic amounts. Ti(III) could be substituted by reduced ferredoxin. ATP could not be substituted by AMP, CTP, GTP, S-adenosylmethionine, or by ATP analogues. The membrane fraction was methylated by CH3–H4MPT in the absence of H–S–CoM. This methylation was dependent on Ti(III) and ATP. The methylated membrane fraction catalyzed the methyltransfer from CH3–H4MPT to H–S–CoM in the absence of ATP and Ti(III). Demethylation in the presence of H–S–CoM also did not require Ti(III) or ATP. Based on these findings a mechanism for the methyltransfer reaction and for the activation of the enzyme is proposed.Abbreviations H4MPT tetrahydromethanopterin - CH3–H4MPT N 5-methyl-H4MPT - H–S–CoM 2-mercaptoethanesulfonate or coenzyme M - CH3–S–CoM 2(methylthio)ethanesulfonate or methylcoenzyme M - SDS-PAGE sodium dodecylsulfate polyacrylamide gel electrophoresis - DTT dithiothreitol - MOPS morpholinopropanesulfonate - CHAPS 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane-sulfonate - 1 U = 1 mol/min  相似文献   

18.
The basis for the outcome of competition between sulfidogens and methanogens for H2 was examined by comparing the kinetic parameters of representatives of each group separately and in co-culture. Michaelis-Menten parameters (V max and K m) for four methanogens and five sulfate-reducing bacteria were determined from H2-depletion data. Further, Monod growth parameters (max, K s, Y H2) for Desulfovibrio sp. G11 and Methanospirillum hungatei JF-1 were similarly estimated. H2 K m values for the methanogenic bacteria ranged from 2.5 M (Methanospirillum PM1) to 13 M for Methanosarcina barkeri MS; Methanospirillum hungatei JF-1 and Methanobacterium PM2 had intermediate H2 K m estimates of 5 M. Average H2 K m estimates for the five sulfidogens was 1.2 M. No consistent difference among the V max estimates for the above sulfidogens (mean=100 nmol H2 min-1 mg-1 protein) and methanogens (mean=110 nmol H2 min-1 mg-1 protein) was found. A two-term Michaelis-Menten equation accurately predicted the apparent H2 K m values and the fate of H2 by resting co-cultures of sulfate-reducers and methanogens. Half-saturation coefficients (K s) for H2-limited growth of Desulfovibrio sp. G11 (2–4 M) and Methanospirillum JF-1 (6–7 M) were comparable to H2 K m estimates obtained for these organisms. Maximum specific growth rates for Desulfovibrio sp. G11 (0.05 h-1) were similar to those of Methanospirillum JF-1 (0.05–0.06 h-1); whereas G11 had an average yield coefficient 4 x that of JF-1. Calculated max and V max/K m values for the methanogens and sulfidogens studied predict that the latter bacterial group will process more H2 whether these organisms are in a growing or resting state, when the H2 concentration is in the first-order region.  相似文献   

19.
Desulfovibrio vulgaris (Marburg) and Methanobrevibacter arboriphilus (AZ) are anaerobic sewage sludge bacteria which grow on H2 plus sulfate and H2 plus CO2 as sole energy sources, respectively. Their apparent Ks values for H2 were determined and found to be approximately 1 M for the sulfate reducing bacterium and 6 M for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal V max) the rate of H2 consumption by D. vulgaris was five times that of M. arboriphilus, when the hydrogen supply was rate limiting. The apparent inhibition of methanogenesis was of the same order as expected from the different Ks values for H2. Difference in substrate affinities can thus account for the inhibition of methanogenesis from H2 and CO2 in sulfate rich environments, where the H2 concentration is well below 5 M.  相似文献   

20.
The effect of 2-hydroxybenzoate (2-OHB, salicylate) on the mineralization rate of [14C]naphthalene, the population density of naphthalene-degrading bacteria, and the concentration of genes encoding for naphthalene dioxygenase in a soil bacterial community was investigated. Six different concentrations of 2-OHB (10, 20, 50, 100, 150 and 200 g g–1 soil) were tested in 100-g portions of soil. The addition of 10, 20 or 50 g 2-OHB g–1 soil produced a general increase in total soil bacterial population density, whereas the addition of 100 g or 200 g 2-OHB g–1 soil specifically increased the proportion of naphthalene degraders relative to the total population. The addition of 50 g 2-OHB g–1 soil produced a fourfold increase (the maximum observed) in the rate of naphthalene mineralization relative to the rate in unamended soil. The concentration of 2-OHB ( 100 g/g) added to soil correlated with the population density of naphthalene degraders (r=0.961). Addition of up to 200 g 2-OHB g–1 correlated with the abundance of DNA sequences homologous to known naphthalene dioxygenase genes (nahAB) (r=0.958). However, mineralization of [14C]naphthalene was stimulated significantly only by the addition of 50 g 2-OHB g–1 soil. Results of the mineralization experiments were supported by the detection of nahAB mRNA extracted directly from soil. The specificity of the effect of 2-OHB on naphthalene biodegradation was confirmed in a control experiment using equivalent concentrations of 4-OHB which repressed naphthalene mineralization by about 50%. Addition of ammonium nitrate to the soil also increased the rate of naphthalene mineralization. Ammonium nitrate added together with 2-OHB reduced the mineralization enhancement effect of either compound alone. The study confirmed that specific induction of biodegradative genes can enhance chemical pollutant removal in situ. Correspondence to: O. A. Ogunseitan  相似文献   

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