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1.
2.
Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods 总被引:7,自引:1,他引:6
Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and15N based methods as well as undisturbed soil core andin situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.Discussions of the importance of denitrification have always focused on quantifying the process and whether particular measured quantities are judged to be a significant amount of nitrogen. A second line of evidence discussed here is the extant genetic record that results from natural selection. These analysis lead to the conclusion that strong selection for denitrification must currently be occurring, which implies that the process is of general significance in soils. 相似文献
3.
Immunological identification and distribution of dissimilatory heme cd1 and nonheme copper nitrite reductases in denitrifying bacteria 总被引:4,自引:0,他引:4
M S Coyne A Arunakumari B A Averill J M Tiedje 《Applied and environmental microbiology》1989,55(11):2924-2931
Polyclonal antibodies were used to identify heme or copper nitrite reductases in the following groups: 23 taxonomically diverse denitrifiers from culture collections, 100 numerically dominant denitrifiers from geographically diverse environments, and 51 denitrifiers from a culture collection not selected for denitrification. Antisera were raised against heme nitrite reductases from Pseudomonas aeruginosa and Pseudomonas stutzeri and against copper nitrite reductase from Achromobacter cycloclastes. Nitrite reductases were identified by Western immunoblot. Diethyldithiocarbamate, which specifically inhibits copper nitrite reductases, was used to confirm the immunological characterization and determine which type was present in strains nonreactive with any antiserum. For groups in which the type of nitrite reductase has not been previously described, we found that Alcaligenes eutrophus, Bacillus azotoformans, Bradyrhizobium japonicum, Corynebacterium nephridii, and Rhizobium spp. contained copper nitrite reductase, while Aquaspirillum itersonii, Flavobacterium spp., and Pseudomonas fluorescens contained heme nitrite reductase. Heme nitrite reductases dominated, regardless of soil type or geographic origin. They occurred in 64 and 92%, respectively, of denitrifiers in the numerically dominant and nonselected collections. The two nitrite reductase types were mutually exclusive in individual bacteria, but both appeared in different strains from the Alcaligenes and Pseudomonas genera. The heme type predominated in Pseudomonas strains. The heme-type nitrite reductase appeared more conserved if judged by similarities in molecular weights and immunological reactions. The Cu type was found in more taxonomically unrelated strains and varied in molecular weight and antiserum recognition. 相似文献
4.
Strain DCB-1 conserves energy for growth from reductive dechlorination coupled to formate oxidation 总被引:26,自引:0,他引:26
Strain DCB-1 is a strict anaerobe capable of the reductive dechlorination of chlorobenzoates. The effect of dechlorination on the yield of pure cultures of DCB-1 was tested. Cultures were incubated with formate or H2 as electron donors and CO2 as a putative carbon source. Relative to control cultures with benzoate, cultures which dechlorinated 3-chlorobenzoate and 3,5-dichlorobenzoate had higher yields measured both as protein and cell density. On the media tested the apparent growth yield was 1.7 to 3.4 g cell protein per mole Cl- removed. Dechlorination also stimulated formate oxidation by growing cultures. Resuspended cells required an electron donor for dechlorination activity, with either formate or elemental iron serving this function. Resuspended cells did not require an electron acceptor for formate consumption, but reductive dechlorination of 3CB to benzoate stoichiometrically stimulated oxidation of formate to CO2. These results indicate that DCB-1 conserves energy for growth by coupling formate, and probably, H2 oxidation to reductive dechlorination.Non-standard abbreviations 3CB
3-chlorobenzoate
- 35DCB
3,5-dichlorobenzoate
- PCF
Propionibacterium sp. culture fluid 相似文献
5.
Oxygen control prevents denitrifiers and barley plant roots from directly competing for nitrate 总被引:1,自引:0,他引:1
Abstract Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O2 concentration on denitrification and NO3 − uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O2 concentration in the solution. Both Pseudomonads lacked N2 O reductase and so total denitrification could be directly measured as N2 O production.
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O2 saturation (0.14 μM O2 ) and was totally inhibited at 0.04% O2 saturation (0.56 μM O2 ). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO3 − uptake rate decreased gradually from a maximum in 21% O2 -saturated medium (air saturated) to zero at 1.6% O2 saturation (22.4 μM O2 ). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur. 相似文献
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O
6.
Physiological characterization of strain DCB-1, a unique dehalogenating sulfidogenic bacterium 总被引:7,自引:0,他引:7
Strain DCB-1 is an obligately anaerobic bacterium which carries out the reductive dehalogenation of halobenzoates and was previously known to grow only on pyruvate plus 20% ruminal fluid. When various electron acceptors were supplied, thiosulfate and sulfite were found to stimulate growth. Sulfide was produced from thiosulfate. Cytochrome c and desulfoviridin were detected. The mol% G+C was 49 (at the thermal denaturation temperature). Of 55 carbon sources tested, only pyruvate supported growth as the sole carbon source in mineral medium. Lactate, acetate, L- and D-malate, glycerol, and L- and D-arabinose stimulated growth when supplemented with 10% ruminal fluid and 20 mM thiosulfate. In mineral medium, pyruvate was converted to acetate and lactate, with small amounts of succinate and fumarate accumulating transiently. During growth with thiosulfate, all of these products accumulated transiently. Addition of excess hydrogen to pyruvate-grown cultures resulted in diversion of carbon to formate, lactate, and butyrate, which caused a decrease in cell yield. We conclude that strain DCB-1 is a new type of sulfidogenic bacterium. 相似文献
7.
Sub-Parts-Per-Billion Nitrate Method: Use of an N2O-Producing Denitrifier to Convert NO3− or 15NO3− to N2O 下载免费PDF全文
A more sensitive analytical method for NO3− was developed based on the conversion of NO3− to N2O by a denitrifier that could not reduce N2O further. The improved detectability resulted from the high sensitivity of the 63Ni electron capture gas chromatographic detector for N2O and the purification of the nitrogen afforded by the transformation of the N to a gaseous product with a low atmospheric background. The selected denitrifier quantitatively converted NO3− to N2O within 10 min. The optimum measurement range was from 0.5 to 50 ppb (50 μg/liter) of NO3− N, and the detection limit was 0.2 ppb of N. The values measured by the denitrifier method compared well with those measured by the high-pressure liquid chromatographic UV method above 2 ppb of N, which is the detection limit of the latter method. It should be possible to analyze all types of samples for nitrate, except those with inhibiting substances, by this method. To illustrate the use of the denitrifier method, NO3− concentrations of <2 ppb of NO3− N were measured in distilled and deionized purified water samples and in anaerobic lake water samples, but were not detected at the surface of the sediment. The denitrifier method was also used to measure the atom% of 15N in NO3−. This method avoids the incomplete reduction and contamination of the NO3− -N by the NH4+ and N2 pools which can occur by the conventional method of 15NO3− analysis. N2O-producing denitrifier strains were also used to measure the apparent Km values for NO3− use by these organisms. Analysis of N2O production by use of a progress curve yielded Km values of 1.7 and 1.8 μM NO3− for the two denitrifier strains studied. 相似文献
8.
9.
Degradation of ethylene glycol and polyethylene glycols by methanogenic consortia. 总被引:8,自引:4,他引:4 下载免费PDF全文
Methanogenic enrichments capable of degrading polyethylene glycol and ethylene glycol were obtained from sewage sludge. Ethanol, acetate, methane, and (in the case of polyethylene glycols) ethylene glycol were detected as products. The sequence of product formation suggested that the ethylene oxide unit [HO-(CH2-CH2-O-)xH] was dismutated to acetate and ethanol; ethanol was subsequently oxidized to acetate by a syntrophic association that produced methane. The rates of degradation for ethylene, diethylene, and polyethylene glycol with molecular weights of 400, 1,000, and 20,000, respectively, were inversely related to the number of ethylene oxide monomers per molecule and ranged from 0.84 to 0.13 mM ethylene oxide units degraded per h. The enrichments were shown to best metabolize glycols close to the molecular weight of the substrate on which they were enriched. The anaerobic degradation of polyethylene glycol (molecular weight, 20,000) may be important in the light of the general resistance of polyethylene glycols to aerobic degradation. 相似文献
10.