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排序方式: 共有63条查询结果,搜索用时 15 毫秒
1.
Immunogenicity of Brucella abortus salt-extractable proteins 总被引:5,自引:0,他引:5
The immunogenic properties of salt-extractable proteins and chromatographic fractions thereof from Brucella abortus were evaluated in lemmings (Dicrostonyx rubricatus). The efficacy of the Brucella proteins as immunogens was determined after challenge with virulent B. abortus strain 2308 and was based on protection against clinical signs and gross lesions of brucellosis, as well as on numbers of viable Brucella in the spleen. Vaccination of lemmings with as little as 0.1 microgram of salt-extractable proteins (CSP) suppressed splenic infection, resulting in reduced numbers of viable organisms per spleen of 5-6 logs compared to non-vaccinated controls. Protein fractions separated by column chromatography were generally effective in reducing splenic infection, and contained proteins with molecular weights of 30,000, 20,000 and 12,000. Vaccines containing chemically modified dodecanoyl-CSP offered no additional advantage over unmodified CSP vaccines. 相似文献
2.
3.
Summary This study compares N mineralization in soils treated with crop residues [corn (Zea mays L.), soybean (Glycine max (L.) Merr.), sorghum (Sorghum vulgare Pers.)] or alfalfa (Medicago sativa L.) at three adjusted soil pH values (4, 6, and 8); pH was adjusted with dilute H2SO4 or KOH. A sample of soil (20 g) was treated with 0.448 g plant material (equivalent to 50t ha–1), mixed with 20 g silica sand adjusted to the pH of the soil, and packed in a leaching tube. The soil-sand mixture was leached with 100 ml 5 mM CaCl2 adjusted to the same pH as that of the treated soil to remove the initial mineral N, and incubated at 30°C. The leaching procedure was repeated every 2 weeks for 20 weeks. Results from three soils showed that N mineralization increased as the soil pH increased. In one soil (Lester soil), significant amounts of NH
4
+
-N accumulated at pH 4 during the first 12 weeks. Treatment with corn and soybean residues resulted in a marked reduction in N mineralization, especially at pH 4. The percentage of organic N mineralized from sorghum residue and alfalfa added to soils increased as the soil pH increased; the values ranged from 7.7% to 37.0% for sorghum and from 17.2% to 30.1% for alfalfa. 相似文献
4.
Effect of tillage and residue management on enzyme activities in soils 总被引:14,自引:3,他引:14
Recent interest in soil tillage and residue management has focused on low-input sustainable agriculture. In this study we investigated the effect of three tillage systems (no-till, chisel plow, and moldboard plow) and four residue placements (bare, normal, mulch, and double mulch) on the activities of four amidohydrolases (amidase, L-asparaginase, L-glutaminase, and urease) in soils from four replicated field-plots. Correlation coefficients (r) for linear regressions between the activities of each of the enzymes and organic C or pH and between all possible paired amidohydrolases were also calculated. The results showed that the effects of tillage and residue management on pH in the 28 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different tillage and residue-management practices studied, being the greatest in soils with notill/double mulch treatment, and the least with no-till/bare and moldboard/normal treatments. Within the same tillage system, mulch treatment resulted in greater organic C content compared with normal or bare treatment. The activities of the amidohydrolases studied were generally greater in mulch-treated plots than in non-treated plots, and were significantly correlated with organic C contents of soils, with r values ranging from 0.70*** to 0.90***. Linear regression analyses of enzyme activities on pH values (in 0.01 M CaCl2) of the 28 surface soils showed significant correlations for L-asparaginase, L-glutaminase, and urease, with r values of 0.74***, 0.77***, and 0.72***, respectively, but not for amidase (r=0.24). The activities of the four amidohydrolases studied in the 40 soil samples tested were significantly intercorrelated, with r values ranging from 0.72*** to 0.92***. The activities of the four amidohydrolases decreased with increasing soil depth of the plow layer, and were accompanied by a decrease in organic C content. 相似文献
5.
This study was carried out to investigate the long‐term influence of lime application and tillage systems (no‐till, ridge‐till, and chisel plow) on the activities of phosphatases and arylsulfatase in soils at four research sites in Iowa, USA. The activities of the following enzymes were studied: acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase at their optimal pH values. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r ranged from –0.65** to –0.98***), the activities of other enzymes were significantly (P < 0.001) and positively correlated with soil pH, with r values ranging from 0.65** to 0.99*** for alkaline phosphatase, from 0.79*** to 0.97*** for phosphodiesterase, and from 0.66*** to 0.97*** for arylsulfatase. The Δ activity/Δ pH values were calculated to determine the sensitivity of each enzyme to changes in soil pH. Acid phosphatase was the most sensitive and arylsulfatase the least sensitive to changes in soil pH. Activities of the enzymes were greater in the 0 – 5 cm depth samples than those in 0 – 15 cm samples under no‐till treatment. With the exception of acid phosphatase, enzyme activities were mostly significantly (P < 0.001) and positively correlated with microbial biomass C (Cmic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (Nmic), with r values ranging from 0.31 (not significant) to 0.94***. Liming and tillage systems significantly affected the activities of some enzymes but not others, as was evident from the specific activity values (g of p‐nitrophenol released kg–1 Corg h–1). 相似文献
6.
l-Asparaginase activity of soils 总被引:1,自引:0,他引:1
Summary A simple, precise, and sensitive method to assay l-asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) activity in soils is described. This method use steam distillation to determine the NH
inf4
sup+
produced by l-asparaginase activity when soil is incubated with buffered (0.1 M THAM, pH 10) l-asparagine solution and toluene at 30°C for 2 h. The procedure developed gives quantitative recovery of NH
inf4
sup+
-N added to soils and does not cause chemical hydrolysis of l-asparagine. The optimum buffer pH for NH
inf4
sup+
-N released by l-asparaginase activity in soils was 10. This enzyme was saturated with 50 mM
l-asparagine, and the reaction rate essentially followed zero-order kinetics. The d-isomer of asparagine was also hydrolyzed in soils, but at only 16% of the activity of the l-isomer at a saturating concentration of the substrate. The optimal temperature for the soil l-asparaginase reaction occurred at 60°C and denaturation began at 65°C. The Arrhenius equation plot for l-asparaginase activity in three selected soils was linear between 10 and 50°C. The activation energy values of this enzyme ranged from 20.2 to 34.1 (average 26.6) kJ mol-1. Application of three linear transformations of the Michaelis-Menten equation showed that the K
m values of l-asparaginase in nine soils ranged from 2.6 to 10.0 (average 6.1) mM and the V
max values ranged from 9 to 131 g NH
inf4
sup+
-N released g-1 soil 2 h-1. The temperature coefficients (Q
10) for soil l-asparaginase activity ranged from 1.12 to 1.70 (average 1.39). Steam sterilization (121°C for 1 h), formaldehyde, and NaF decreased the activity but the presence of toluene increased the amount of NH
inf4
sup+
released. Treatment of soils with dimethylsulfoxide completely destroyed l-asparaginase activity. The use of sulfhydryl reagents indicated that a free sulfhydryl moiety was required to maintain the active enzyme. l-Asparaginase activity in soils was increased by 13 to 18% in the presence of THAM buffer prepared to contain 5 mM Ca2+ and Mg2+, respectively. 相似文献
7.
Reconstructing past ocean pH-depth profiles 总被引:1,自引:0,他引:1
Measurement of boron isotope compositions in species of planktonic foraminifera that calcified their tests at different depths in the water column are used to reconstruct the pH profile of the upper water column of the tropical ocean. Results for five time windows from the middle Miocene to the late Pleistocene indicate pH-depth profiles similar to that of the modern ocean in this area, which suggests that this method may greatly aid in our understanding of the global carbon cycle. 相似文献
8.
ZF Ren ZP Huang JW Xu JH Wang P Bush MP Siegal PN Provencio 《Science (New York, N.Y.)》1998,282(5391):1105-1107
Free-standing aligned carbon nanotubes have previously been grown above 700 degreesC on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666 degreesC by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0. 1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication. 相似文献
9.
The impacts of crop rotations and N fertilization on microbial biomass C (Cmic) and N (Nmic) were studied in soils of two long-term field experiments initiated in 1978 at the Northeast Research Center (NERC) and in
1954 at the Clarion-Webster Research Center (CWRC), both in Iowa. Surface soil samples were taken in 1996 and 1997 from plots
of corn (Zea mays L.), soybeans (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha–1 before corn and an annual application of 20 kg P and 56 kg K ha–1. The Cmic and Nmic values were determined by the chloroform-fumigation-extraction method and the chloroform-fumigation-incubation method, respectively.
The Cmic and Nmic values were significantly affected (P<0.05) by crop rotation and plant cover at time of sampling, but not by N fertilization. In general, the highest Cmic and Nmic contents were found in the multicropping systems (4-year rotations) taken in oats or meadow plots, and the lowest values
were found in continuous corn and soybean systems. On average, Cmic made up about 1.0% of the organic C (Corg), and Nmic contributed about 2.4% of the total N (Ntot) in soils at both sites and years of sampling. The Cmic values were significantly correlated with Corg contents (r≥0.41**), whereas the relationship between Cmic and Ntot was significant (r≤0.53***) only for the samples taken in 1996 at the NERC site. The Cmic : Nmic ratios were, on average, 4.3 and 6.4 in 1996, and 7.6 and 11.4 in 1997 at the NERC and CWRC sites, respectively. Crop rotation
significantly (P<0.05) affected this ratio only at the NERC site, and N fertilization showed no effect at either site. In general, multicropping
systems resulted in greater Cmic : Corg (1.1%) and Nmic : Ntot (2.6%) ratios than monocropping systems (0.8% and 2.1%, respectively).
Received: 9 February 1999 相似文献
10.