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1.
Electron transport system (ETS) activity, CO 2 evolution, O 2 consumption, N 2-fixation (C 2H 2 reduction) and methanogenesis were appropriately measured in aerobic and anaerobically incubated sediment at 4, 10 and 20 ° C to better characterize these activities under different incubation conditions. ETS activity was always higher in the aerobically incubated sediment at all three incubation temperatures, whereas (C 2H 2 reduction was always greater in the anaerobic sediment. Carbon dioxide evolution was detected only in the aerobic sediment at 10 and 20 ° C but not at 4 ° C. Methane evolution in anaerobic sediment increased gradually with an increase in the incubation temperature. 相似文献
2.
Detached cowpea nodules that contained a nitrous oxide reductase-positive (Nor +) rhizobium strain (8A55) and a nitrous oxide reductase-negative (Nor −) rhizobium strain (32H1) were incubated with 1% 15N 2O (95 atom% 15N) in the following three atmospheres: (i) aerobic with C 2H 2 (10%), (ii) aerobic without C 2H 2, and (iii) anaerobic (argon atmosphere) without C 2H 2. The greatest production of 15N 2 occurred anaerobically with 8A55, yet very little was formed with 32H1. Although acetylene reduction activity was slightly higher with 32H1, about 10 times more 15N 2 was produced aerobically by 8A55 than by 32H1 in the absence of acetylene. The major reductive pathway of N 2O reduction by denitrifying rhizobium strain 8A55 is by nitrous oxide reductase rather than nitrogenase. 相似文献
3.
Summary Nitrogen fixation in the natural, Agropyron-Koeleria grassland ecosystem was studied using the C 2H 2-C 2H 4 and N 15 assays. Small soil samples and also undisturbed soil cores were used for analyses. Both techniques indicated that grassland
and associated cultivated soils had low fixation rates (0.6–1.8 kg/ha per 28 days in the laboratory and, 1 kg/ha per season
under actual field conditions). Algal colonies ( Nostoc spp.) on the soil surface were active fixers when the surface of the grassland was moist. However, their small biomass limits
the extent of fixation in most areas.
In native grassland, 16 legumes bore nodules. The three most common species Vicia americana, Thermopsis rhombifolia and Oxytropis sericea, all of which had active nodules, contributed 10 per cent of the total nitrogenase activity.
The non-legumes Elaeagnus commutata and Shepherdia argentea were profusely nodulated with active nodules, but were confined to specific habitats. No nodules were found on Artemisia or Opuntia spp.
The major, heterotrophic, asymbiotic bacteria in the soil were clostridia. These utilize substrates produced by aerobic cellulose
and hemicellulose degrading organisms to fix N in anaerobic microsites. The C 2H 2:N 2 reduction ratio was 3 to 1 in large, aerobic core samples, but was greater under water-logged conditions where high fixation
rates occurred. 相似文献
4.
The effects of C 2H 2 metabolism on N 2O production were examined in soil slurries. Enrichment of C 2H 2 consumption activity occurred only in aerobic incubations. Rapid disappearance of subsequent C 2H 2 additions, stimulation of CO 2 production, and most-probable-number enumerations of C 2H 2 utilizers indicated enrichment of the population responsible. During C 2H 2 consumption in slurries incubated statically under air, maximal rates of N 2O evolution were 19 times higher than those in anaerobic incubations. After 20 days of enrichment with C 2H 2, the production of N 2O by slurries supplemented with C 2H 2 and nitrate was 10 times higher than that in the unenriched controls. A Nocardia- or Arthrobacter-like bacterium was isolated that grew on C 2H 2 but did not denitrify. The behavior of soil inoculated with this bacterium became similar to that of C 2H 2-enriched soil incubated aerobically. Ethanol, acetate, and acetaldehyde were identified in enrichment experiments, and denitrification in soil slurries was stimulated by addition of the supernatant from a pure culture grown on mineral medium with C 2H 2. These results indicate that denitrification can be stimulated by the actions of an aerobic, nondenitrifying C 2H 2-metabolizing population. Utilization of intermediate metabolites by denitrifiers and enhanced O 2 consumption are two possible mechanisms for this stimulation. 相似文献
5.
Summary Aerobic and anaerobic N 2-fixing bacteria developed in the rhizosphere of barley seedlings and exhibited N 2ase activity when seedlings were grown in sterilized sand-nutrient cultures containing low levels of combined nitrogen. The
source of the N 2-fixing bacteria appeared to be the seed. Average daily rates up to 0.9 μmoles C 2H 4 h −1 g −1 dry root tissue were measured, but the intensity of the activity was affected by moisture levels and concentration of combined
N in the rhizosphere. Removal and washing of the roots did not remove the activity, and roots remained active even after surface-sterilization.
An unidentified aerobic N 2-fixing bacterium was isolated from the rhizoplane of active barley roots. Inoculation of barley seedlings with the aerobic
N 2-fixing bacterium enhanced N 2ase activity of excised roots 10-fold, with average rates of 0.9, 1.1 and 1.3 μmoles h −1 g −1 dry root assayed under pO 2 of 0.01, 0.02 and 0.04 atm respectively. The aerobic N 2-fixing bacterium also exhibited N 2ase activity when inoculated into the rhizosphere of oat, rice and wheat seedlings. Microscopic observations of sterilized
live and stained barley roots suggest that the aerobic N 2-fixing bacterium is an endophyte which infects root tissue and metamorphoses into vesicle-like structures. 相似文献
6.
Oscillatoria limnetica grown photoautotrophically under aerobic or anaerobic conditions contained a single superoxide dismutase (SOD) of identical electrophoretic mobility in both cases. Its activity was cyanide resistant and H 2O 2 sensitive, implicating Fe-SOD. The enzyme level was high in aerobically and low in anaerobically growing cells. Anaerobically grown cells were more sensitive than aerobic to photooxidation, as expressed by bleaching of phycocyanin and disintegration of the trichomes.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- SOD
superoxide dismutase 相似文献
7.
Nitrogen fixation was associated with the rinsed roots and rhizomes of the seagrass, Zostera marina L. Nitrogenase activity (acetylene reduction) was greater on rhizomes compared to roots, and on older roots and rhizomes relative to younger tissue. Compared to aerobic assays, anaerobic or microaerobic conditions enhanced the rate of acetylene reduction by rhizomes with attached roots, with the highest activity (100 nanomoles per gram dry weight per hour) occurring at pO 2 = 0.01 atmosphere. Addition of glucose, sucrose, or succinate also increased the rate of acetylene reduction under anaerobic conditions, with glucose providing the most stimulation. In one experiment, comparison of acetylene reduction assays with 15N 2 incorporation yielded a ratio of about 2.6:1. Seagrass communities are thought to be limited by the availability of nitrogen and, therefore, nitrogenase activity directly associated with their roots and rhizomes suggests the possibility of a N 2-fixing flora which may subsidize their nutritional demand for nitrogen. 相似文献
8.
High rates of acetylene (C 2H 2) reduction (nitrogenase activity) were observed in woodroom effluent from a neutral sulfite semi-chemical mill under aerobic (up to 644 nmol of C 2H 4 produced per ml per h) and under anaerobic (up to 135 nmol of C 2H 4 produced per ml per h) conditions. Pasteurized effluent developed C 2H 2 reduction activity when incubated under anaerobic but not under aerobic conditions. Activities were increased by addition of 0.5 to 3.0% glucose or xylose. Enrichment and enumeration studies showed that N 2-fixing Azotobacter and Klebsiella were abundant, and N 2-fixing Bacillus was present. Of 129 isolates of Klebsiella from pulp mills, lakes, rivers, and drainage and sewage systems, 32% possessed nitrogen-fixing ability. 相似文献
9.
Samples of sediment from Lake St. George, Ontario, Canada, were incubated in the laboratory under an initially aerobic gas phase and under anaerobic conditions. In the absence of added nitrate (NO 3−) there was O 2-dependent production of nitrous oxide (N 2O), which was inhibited by acetylene (C 2H 2) and by nitrapyrin, suggesting that coupled nitrification-denitrification was responsible. Denitrification of added NO 3− was almost as rapid under an aerobic gas phase as under anaerobic conditions. The N 2O that accumulated persisted in the presence of 0.4 atm of C 2H 2, but was gradually reduced by some sediment samples at lower C 2H 2 concentrations. Low rates of C 2H 2 reduction were observed in the dark, were maximal at 0.2 atm of C 2H 2, and were decreased in the presence of O 2, NO 3−, or both. High rates of light-dependent C 2H 2 reduction occurred under anaerobic conditions. Predictably, methane (CH 4) production, which occurred only under anaerobiosis, was delayed by added NO 3− and inhibited by C 2H 2. Consumption of added CH 4 occurred only under aerobic conditions and was inhibited by C 2H 2. 相似文献
10.
When seeds of Echinochloa crusgalli var. oryzicola are germinated in dark anaerobic conditions (99.995% N 2), the seedlings do not have detectable protochlorophyll(ide). Two hours after exposure to light aerobic conditions, they begin to synthesize chlorophyll. The lag in greening is shorter in seedlings exposed to light for 24 hours before exposure to air. Seedlings maintained in light anaerobic conditions exhibit no lag in greening upon transfer to an aerobic environment. Preillumination of anaerobically grown seedlings does not result in any chlorophyll accumulation. Phytochrome is probably the receptor for photoactivation of chlorophyll synthesis, since activation is achieved by red light alone, but not by far red light or red plus far red light. The cytochrome oxidase activity in anaerobically germinated seedlings is 30% of the normal level found in aerobically grown seedlings. Preillumination was also found to activate the ability of anaerobically germinated seedlings to increase their cytochrome oxidase activity upon exposure to air. 相似文献
11.
Summary Among 390 isolates from Egytiian soils initially grown on Brown's N-free agar, 15 facultative Bacillus isolates were able to reduce acetylene in Stanier's N-poor broth under both aerobic and anaerobic (N 2 atmosphere) conditions. Some of these isolates were Gram-positive, with unswollen sporangia and thin-walled endospores. Other strains were with slightly or definitely bulged sporangia. Yeast extract (0.01%) was essential for growth stimulation and N 2[C 2H 2] fixation by these isolates. Replacing yeast extract with 20 g/ml (NH 4) 2SO 4 or biotin, thiamine and amino acids (singly or in combination) resulted in stimulation of growth and N 2[C 2H 2] fixation, though at lower rates than in yeast extract.One isolate was able to grow and reduce C 2H 2 in Stanier's N-free liquid medium. Nitrogenase [C 2H 2] activity of the anaerobically grown and incubated cultures was greater than aerobic cultures. Addition of 0.1% CaCO 3 to the culture media significantly increased and O 2 partially inhibited, N 2[C 2H 2] fixation by these Bacillus isolates.Studies of the characteristics and N 2[C 2H 2] fixing activities of these isolates indicate that at least some of them are new nitrogen-fixing Bacillus species. 相似文献
12.
Aquaspirillum magnetotacticum strain MS-1 and two nonmagnetic mutants derived from it reduced C 2H 2 microaerobically but not anaerobically even with NO 3 ?. This organism apparently is not capable of NO 3 ?-dependent nitrogen fixation. Cells of A. magnetotacticum reduced C 2H 2 at rates comparable to those of Azospirillum lipoferum grown under similar conditions, but much lower than that of Azotobacter vinelandii grown aerobically. Cells of A. magnetotacticum in anaerobic cultures lacking NO 3 ? did not reduce C 2H 2 until O 2 was introduced. Optimum rates of C 2H 2 reduction by A. magnetotacticum were obtained at 200 Pa O 2. C 2H 2 reduction was inhibited by more than 1 kPa O 2 or 0.2 m M NO 3 ? or NH 4 +. These results suggest that A. magnetotacticum fixes N 2 only under microaerobic, N-limited conditions. 相似文献
13.
Summary Gas chromatographic analysis of hydrogen in non-sterile soil incubated aerobically and anaerobically revealed that consumption of the gaseous hydrogen correlated very highly with the initial hydrogen substrate concentration. Hydrogen consumption was not observed in sterile soil. In anaerobically incubated soil, methane evolution was not related to H 2 consumption. The optimum temperature range for H 2 consumption in both aerobic and anaerobically incubated soil was between 20 and 30°C. Activity rapidly decreased at soil temperatures above and below this optimum temperature range. 相似文献
14.
Raising the pO 2 reduced nitrogenase activity (C 2H 2 reduction) of Anabaena cylindrica for both glyoxylate-treated (5 mM) and untreated cells. The stimulation caused by glyoxylate, however, increased with increases of pO 2 from 2 to 99 kPa. As the pO 2 increased the net CO 2 fixation was lowered (Warburg effect) while the CO 2 compensation point increased. Glyoxylate partly relieved this sensitivity of net photosynthesis to oxygen and reduced the compensation point considerably. The cells used were preincubated in the dark to exhaust photosynthetic pools. A more pronounced reduction in sensitivity of nitrogenase to oxygen for glyoxylate-treated cells was evident when a preincubation in air with reduced pCO 2 (13 l l -1) was used. This was, however, not evident until after a 10-h incubation in air. Before this point 2 kPa O 2 sustained the highest nitrogenase activity. Addition of 0.5 and 5 mM of HCO
3
-
to Anabaena cultures preincubated at low CO 2 levels (29 l l -1) abolished the stimulatory effect of glyoxylate on the nitrogenase. Thus, the results sustain the suggestion that glyoxylate may act as an inhibitor of photorespiratory activities in cyanobacteria and can be used as a means of increasing their nitrogen and CO 2 fixation capacities.Abbreviation RuBP
ribulose 1,5-bisphosphate 相似文献
15.
The methodology, characteristics and application of the sensitive C 2H 2-C 2H 4 assay for N 2 fixation by nitrogenase preparations and bacterial cultures in the laboratory and by legumes and free-living bacteria in situ is presented in this comprehensive report. This assay is based on the N 2ase-catalyzed reduction of C 2H 2 to C 2H 4, gas chromatographic isolation of C 2H 2 and C 2H 4, and quantitative measurement with a H 2-flame analyzer. As little as 1 μμmole C 2H 4 can be detected, providing a sensitivity 10 3-fold greater than is possible with 15N analysis. A simple, rapid and effective procedure utilizing syringe-type assay chambers is described for the analysis of C2H2-reducing activity in the field. Applications to field samples included an evaluation of N2 fixation by commercially grown soybeans based on over 2000 analyses made during the course of the growing season. Assay values reflected the degree of nodulation of soybean plants and indicated a calculated seasonal N2 fixation rate of 30 to 33 kg N2 fixed per acre, in good agreement with literature estimates based on Kjeldahl analyses. The assay was successfully applied to measurements of N2 fixation by other symbionts and by free living soil microorganisms, and was also used to assess the effects of light and temperature on the N2 fixing activity of soybeans. The validity of measuring N2 fixation in terms of C2H2 reduction was established through extensive comparisons of these activities using defined systems, including purified N2ase preparations and pure cultures of N2-fixing bacteria. With this assay it now becomes possible and practicable to conduct comprehensive surveys of N2 fixation, to make detailed comparisons among different N2-fixing symbionts, and to rapidly evaluate the effects of cultural practices and environmental factors on N2 fixation. The knowledge obtained through extensive application of this assay should provide the basis for efforts leading to the maximum agricultural exploitation of the N2 fixation reaction. 相似文献
16.
Gluconacetobacter diazotrophicus is an N 2-fixing endophyte isolated from sugarcane. G. diazotrophicus was grown on solid medium at atmospheric partial O 2 pressures (pO 2) of 10, 20, and 30 kPa for 5 to 6 days. Using a flowthrough gas exchange system, nitrogenase activity and respiration rate were then measured at a range of atmospheric pO 2 (5 to 60 kPa). Nitrogenase activity was measured by H 2 evolution in N 2-O 2 and in Ar-O 2, and respiration rate was measured by CO 2 evolution in N 2-O 2. To validate the use of H 2 production as an assay for nitrogenase activity, a non-N 2-fixing (Nif −) mutant of G. diazotrophicus was tested and found to have a low rate of uptake hydrogenase (Hup +) activity (0.016± 0.009 μmol of H 2 10 10 cells −1 h −1) when incubated in an atmosphere enriched in H 2. However, Hup + activity was not detectable under the normal assay conditions used in our experiments. G. diazotrophicus fixed nitrogen at all atmospheric pO 2 tested. However, when the assay atmospheric pO 2 was below the level at which the colonies had been grown, nitrogenase activity was decreased. Optimal atmospheric pO 2 for nitrogenase activity was 0 to 20 kPa above the pO 2 at which the bacteria had been grown. As atmospheric pO 2 was increased in 10-kPa steps to the highest levels (40 to 60 kPa), nitrogenase activity decreased in a stepwise manner. Despite the decrease in nitrogenase activity as atmospheric pO 2 was increased, respiration rate increased marginally. A large single-step increase in atmospheric pO 2 from 20 to 60 kPa caused a rapid 84% decrease in nitrogenase activity. However, upon returning to 20 kPa of O 2, 80% of nitrogenase activity was recovered within 10 min, indicating a “switch-off/switch-on” O 2 protection mechanism of nitrogenase activity. Our study demonstrates that colonies of G. diazotrophicus can fix N 2 at a wide range of atmospheric pO 2 and can adapt to maintain nitrogenase activity in response to both long-term and short-term changes in atmospheric pO 2. 相似文献
17.
The N 2-fixing legume nodule requires O 2 for ATP production; however, the O 2 sensitivity of nitrogenase dictates a requirement for a low pO 2 inside the nodule. The effects of long term exposures to various pO 2s on N 2[ C2H2] fixation were evaluated with intact soybean ( Glycine max [L.] Merr., var. Wye) plants. Continuous exposure of their rhizosphere to a pO 2 of 0.06 atmospheres initially reduced nitrogenase activity by 37 to 45% with restoration of original activity in 4 to 24 hours and with no further change in tests up to 95 hours; continuous exposure to 0.02 atmosphere of O 2 initially reduced nitrogenase activity 72%, with only partial recovery by 95 hours. Similar exposures to a pO 2 of 0.32 atmospheres had little effect on N 2[ C2H2] fixation; a pO 2 of 0.89 atmospheres initially reduced nitrogenase activity by 98% with restoration to only 14 to 24% of that of the ambient O 2 controls by 95 hours. Re-exposure to ambient pO 2 of plants adapted to nonambient pO 2s reduced N 2[ C2H2] fixation to similar magnitudes as the reductions which occurred upon initial exposure to variant pO 2 conditions, and a time period was required to readapt to ambient O 2. It is concluded that the N 2[ C2H2]-fixing system of intact soybean plants is able to adapt to a wide range of external pO 2s as probably occur in soil. We postulate that this occurs through an undefined mechanism which enables the nodule to maintain an internal pO 2 optimal for nitrogenase activity. 相似文献
18.
Summary Non-symbiotic heterotrophic N 2 fixation in coniferous bark litter was investigated with the acetylene reduction assay under aerobic and anaerobic conditions. The litter studied was composed essentially of bark, of pH 5 and a C/N ratio of 101; the ratio of available C to available N, which governs N 2 fixation, was considerably higher. The rate of N 2 fixation was estimated as 2.5–4.4 g N. g –1 dry wt. day –1. Nitrogenase activity was still evident after seven months of incubation under aerobic conditions. The N 2-ase activity was O 2 dependent: under anaerobic conditions no N 2-ase activity was found unless a fermentable C source was added. The importance of N 2 fixation in N-poor litter for the maintenance of soil fertility is emphasized. 相似文献
19.
Corn ( Zea mays L.) plants were assayed for nitrogenase activity (C 2H 2 reduction) during early ear development. Hybrid corn and inbred lines were grown separately at two experimental fields in New Jersey. Acetylene-dependent ethylene production was observed a few hours after harvest, from the field, on intact plants, root-soil cores, lower stem segments, and excised roots, all assayed under air and not preincubated previously. Incubation of excised roots at 1% O 2 resulted in lower rates of C 2H 2 reduction. The time course of C 2H 2 reduction by excised roots, assayed in air, was similar for all genotypes studied (two hybrids, eight inbreds, and a cross of corn × teosinte) and indicated that a long preincubation at reduced O 2 is not absolutely required for early detection of nitrogenase activity. Isolation of N 2-fixing bacteria from within the roots and stems, together with the diurnal fluctuation of nitrogenase activity in response to day/night cycles, were indicative of a close association with plant function. Collectively, the results provided strong evidence for the occurrence of nitrogenase activity associated with corn plants growing in a temperate climate and dependent upon indigenous N 2-fixing bacteria. 相似文献
20.
Summary Several Bacillus strains, from the rhizosphere of Ammophila arenaria, appeared on ‘nitrogen-free’ agar plates. They were able to grow in nitrogen-poor medium to which 0.1% yeast extract was
added. Three of these bacilli were tested for their ability to fix nitrogen using the acetylene reduction assay. The C 2H 2-reducing activity was determined at 8-hour intervals during their growth cycle. C 2H 2 reduction (and accordingly N 2 fixation) was greater under anaerobic than aerobic conditions. Additions of 0.1% CaCO 3 significantly increased the C 2H 2-reducing activity under both conditions. Characterisation suggests that these strains are new nitrogen-fixing Bacillus species. re]19740121 相似文献
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