Lachgas(N2O)-Freisetzung durch Streptomyces nitrosporeus in einem sandigen Lehmboden in Abhängigkeit von pO2, pH und Angebot an leicht mineralisierbarem Kohlenstoff

Nitrous oxide (N₂O) release by Streptomyces nitrosporeus in a sandy loam soil as affected by pO₂, pH and amount of easily decomposable organic carbon In model experiments under defined conditions (80%WHC, 300 μg nitrate-N g^?1 dry soil, 30°C) the effect of pO₂, pH and addition of easily decomposable organic matter on nitrous oxide production by Streptomyces nitrosporeus DSM 40023 from a sterilized sandy loam soil was studied. This streptomycete reduces nitrate to N₂O but not to N₂. The strain was inoculated into a sterilized sandy loam soil (pH 6), enriched with nitrate and incubated at approximately 20 and 10% (v/v) O₂ for 26 days. In another series of experiments the pH was increased with NaOH-solution up to pH 7 or the soil was enriched with pulverized leaves (1%) to increase mineralization activity and the demand for electron acceptors. In the headspace the concentration of O₂, CO₂ and N₂O was analysed by GC. The soil concentration of NO₃^?, NO₂^? and NH₄⁺ was measured as well as the pH value. The population density was determined by the plate count method. At a decreased oxygen concentration of about 2.5% (v/v) in the headspace, S. nitrosporeus increased the release of N₂O. In the experiments with an initial oxygen concentration of approximately 20% (v/v) this threshold of about 2.5% /(v/v) O₂ was hardly reached and consequently only little N₂O was produced. Apparently, S. nitrosporeus uses O₂ in preference to nitrate, which is characteristical of nitrate respiration. A pH increase from pH 6 to 7 reduced the lag phase significantly and increased the rate of oxygen consumption, CO₂ release and N₂O production. Maximum nitrous oxide production was reached after 13 days. The result indicated that streptomycetes like S. nitrosporeus may use nitrate alternativly to O₂ to maintain energy conservation (ATP synthesis) with the release of N₂O. So far, nothing is known about the role of streptomycetes in contributing to N₂O production in natural soils.     

畜禽粪便固液分离技术特点及效率评估

该文对常用畜禽粪便固液分离技术进行分析,评估出各分离技术的优缺点、适用对象、分离效果和性价比,为企业选择粪便固液分离设备提供参考。研究结果表明:重力分离技术成本最低,分离粒径小于1 mm的有机物效果最好,但分离后固相含水率过高(90%),一般作为其他技术的预处理。筛分技术对于分离大粒径的有机颗粒物最有效,投资相对小,运行费用低;但对氮磷等营养元素分离效率较低,分离后的固相的含水率偏高,分离产物可用于固态发酵。压滤技术提高了磷元素的分离效率和固相含水率,但运营成本也增加,分离产物可用于有机肥生产。沉淀离心技术对去除细小颗粒最为有效,并能够去除氮磷元素,但运营成本太高,在中国推广难度大。絮凝剂能和大多数的分离技术结合使用从而提高分离效率。所有固液分离技术都不能分离畜禽粪便中的挥发性脂肪酸,因此也不能有效去除液相中的生化需氧量和臭味。多种分离技术的联合使用,在提高营养物质的分离效率的同时,降低固相的含水率将是未来技术发展的主要方向。     

Effects of thiopental sedation on learning and memory

Subjects who were administered thiopental showed a loss of memory for events discussed while they were under sedation. We tested the subjects for recognition memory of pictures and recall of associated pairs of letters and words, and found that the subsequent memory loss was correlated with the concentration of thiopental in the venous blood at the time the material was learned. Retention did not appear to be state-dependent because the subject, while under sedation, could recall material learned prior to sedation, and because recall was not facilitated by reinstatement of the sedation.     

Microtubule stabilization reduces scarring and causes axon regeneration after spinal cord injury

Hypertrophic scarring and poor intrinsic axon growth capacity constitute major obstacles for spinal cord repair. These processes are tightly regulated by microtubule dynamics. Here, moderate microtubule stabilization decreased scar formation after spinal cord injury in rodents through various cellular mechanisms, including dampening of transforming growth factor-β signaling. It prevented accumulation of chondroitin sulfate proteoglycans and rendered the lesion site permissive for axon regeneration of growth-competent sensory neurons. Microtubule stabilization also promoted growth of central nervous system axons of the Raphe-spinal tract and led to functional improvement. Thus, microtubule stabilization reduces fibrotic scarring and enhances the capacity of axons to grow.     

Structure of an HIF-1alpha -pVHL complex: hydroxyproline recognition in signaling

The ubiquitination of the hypoxia-inducible factor (HIF) by the von Hippel-Lindau tumor suppressor (pVHL) plays a central role in the cellular response to changes in oxygen availability. pVHL binds to HIF only when a conserved proline in HIF is hydroxylated, a modification that is oxygen-dependent. The 1.85 angstrom structure of a 20-residue HIF-1alpha peptide-pVHL-ElonginB-ElonginC complex shows that HIF-1alpha binds to pVHL in an extended beta strand-like conformation. The hydroxyproline inserts into a gap in the pVHL hydrophobic core, at a site that is a hotspot for tumorigenic mutations, with its 4-hydroxyl group recognized by buried serine and histidine residues. Although the beta sheet-like interactions contribute to the stability of the complex, the hydroxyproline contacts are central to the strict specificity characteristic of signaling.