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The contribution of nitrifiers and denitrifiers to the nitrous oxide production in slurries of calcareous silt loam and river bank sediment at different oxygen concentrations was determined using acetylene as nitrification inhibitor. The addition of 10 Pa acetylene resulted in inhibition of nitrous oxide production at oxic conditions, but strongly enhanced the nitrous oxide production at oxygen-poor and anoxic conditions. Inhibition of nitrification by short exposure (1 to 24 h) to high concentrations of acetylene (100 Pa to 10 kPa) was tested using the same samples. After the removal of acetylene, nitrification was inhibited almost completely (82% to 89%) for at least 6 days whereas nitrous oxide reduction was restored within a day. It was concluded that the 'short exposure' inhibition method resulted in adequate nitrification inhibit...
Peak emissions of NO and N2O are often observed after wetting of soil. The reactions to sudden changes in the aeration of cultures of nitrifying and denitrifying bacteria with respect to NO and N2O emissions were compared to obtain more information about the microbiological aspects of peak emissions. In continuous culture, the nitrifier Nitrosomonas europaea and the denitrifiers Alcaligenes eutrophus and Pseudomonas stutzeri were cultured at different levels of aeration (80 to 0% air saturation) and subjected to changes in aeration. The relative production of NO and N2O by N. europaea, as a percentage of the ammonium conversion, increased from 0.87 and 0.17%, respectively, at 80% air saturation to 2.32 and 0.78%, respectively, at 1% air saturation. At 0% air saturation, ammonium oxidation and N2O production ceased but NO production was...
Ammonium-oxidizing bacteria of the genus Nitrosospira have often been isolated from acid soils. However, the lower pH-limit for nitrifying activity of these bacteria in pure cultures or in mixed cultures with Nitrobacter sp. is much higher than ambient soil-pH. This study shows that the acid-sensitive, ammonium-oxidizing bacterium Nitrosospira strain AHB1, which has been isolated from an acid heathland soil, could be adapted to oxidize ammonium at pH 4 in the presence of the acid-tolerant nitrite-oxidizing bacterium Nitrobacter strain NHB1. Adaptation could be achieved in two different ways: (I) by immobilizing the bacteria in alginate beads; and (2) by exposing them to pH-fluctuations. Thus, Nitrosospira spp may be involved in the oxidation of ammonium at an ambient low soil-pH, even though they appear to be acid-sensitive after isola...
Biologically active recombinant human follitropin has been expressed in Chinese hamster ovary cells. The carbohydrate chains of the recombinant glycoprotein hormone were enzymatically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. The oligosaccharides were separated from the N-deglycosylated protein by gel-permeation chromatography on Bio-Gel P-100, and fractionated by a combination of FPLC on Mono Q and HPLC on Lichrosorb-NH2. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1-NMR spectroscopy. The following types of carbohydrates occur: monosialylated diantennary (10%), disialylated diantennary (43%), disialylated tri-antennary (5%), trisialylated tri-antennary (13%), trisialylated tri'-antennary (8%), and tetrasialylated tetraantennary (12%) N-acetyllactosamine type of carbohydra...
We studied methane oxidation capacity in soil profiles of Dutch and Finnish coniferous forests. The Finnish sites (n = 9) had nitrogen depositions from 3 to 36 kg N ha⁻¹ a⁻¹. The deposition of N on the Dutch sites (n = 13) was higher ranging from 50 to 92 kg N ha⁻¹ a⁻¹. The Dutch sites had also limed counterparts. Methane oxidation rates were determined by incubating soil samples in the laboratory at +15°C with 10 µl CH₄1⁻¹ (10 ppmv CH₄). In general, CH₄ oxidation rates were highest in the uppermost mineral layers. The average CH₄ oxidation rate in the Finnish mineral soils was three times higher than that in the Dutch soils. The litter layers did not oxidize CH₄. In the Netherlands all organic horizons had a negligible capacity to oxidize CH₄. However, some Finnish organic horizons showed high CH₄ oxidation capacity. In the Netherland...
Influence of oxygen on optical activity and thermal stability of the 1.5 µm emission of Er3+ ions in Si is well documented. Here we support this predominantly phenomenological notion with microscopic evidence. Using two-color and pump-probe spectroscopy with a free-electron laser we establish a direct link between the 1.5 µm emission from Er3+ ions and the 9 µm vibrational band of interstitial oxygen in Si. We show that: i) intensity of the 1.5 µm emission quenches when the 9 µm oxygen vibration is resonantly excited, and ii) the lifetime of the 9 µm vibrational band is affected by Er presence. Both findings evidence microscopic relation of interstitial oxygen and Er and their close proximity in Si matrix.
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