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191.
Healy PC Hocking A Tran-Dinh N Pitt JI Shivas RG Mitchell JK Kotiw M Davis RA 《Phytochemistry》2004,65(16):2373-2378
Chemical investigations of a microfungus Xylaria sp. isolated from the Australian rainforest tree Glochidion ferdinandi have afforded two new natural products, 2-hydroxy-6-methyl-8-methoxy-9-oxo-9H-xanthene-1-carboxylic acid (1) and 2-hydroxy-6-hydroxymethyl-8-methoxy-9-oxo-9H-xanthene-1-carboxylic acid (2). Compound 1 has previously been synthesised but only partially characterised. Methylation of 1 using diazomethane afforded the crystalline compound 2,8-dimethoxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester (3), whose structure was determined by single crystal X-ray analysis. This paper reports the full spectroscopic characterisation of compounds 1-3 by NMR, UV, IR and MS data. All compounds were inactive in a brine shrimp lethality assay and several antimicrobial screens. 相似文献
192.
微生物降解石油烃的功能基因研究进展 总被引:1,自引:3,他引:1
微生物对石油烃的降解在自然衰减去除土壤和地下水石油烃污染的过程中发挥了重要作用。微生物通过其产生的一系列酶来利用和降解这类有机污染物,其中,编码关键降解酶的基因称为功能基因。功能基因可作为生物标志物用于分析环境中石油烃降解基因的多样性。因此,研究石油降解功能基因是分析土著微生物群落多样性、评价自然衰减潜力与构建基因工程菌的重要基础。本文主要介绍了烷烃和芳香烃在有氧和无氧条件下的微生物降解途径,重点总结了烷烃和芳香烃降解的主要功能基因及其作用,包括参与羟化作用的单加氧酶和双加氧酶基因、延胡索酸加成反应的琥珀酸合酶基因以及中心中间产物的降解酶基因等。 相似文献
193.
Paget C Ivanov S Fontaine J Renneson J Blanc F Pichavant M Dumoutier L Ryffel B Renauld JC Gosset P Gosset P Si-Tahar M Faveeuw C Trottein F 《The Journal of biological chemistry》2012,287(12):8816-8829
Invariant natural killer T (iNKT) cells are non-conventional lipid-reactive αβ T lymphocytes that play a key role in host responses during viral infections, in particular through the swift production of cytokines. Their beneficial role during experimental influenza A virus (IAV) infection has recently been proposed, although the mechanisms involved remain elusive. Here we show that during in vivo IAV infection, mouse pulmonary iNKT cells produce IFN-γ and IL-22, a Th17-related cytokine critical in mucosal immunity. Although permissive to viral replication, IL-22 production by iNKT cells is not due to IAV infection per se of these cells but is indirectly mediated by IAV-infected dendritic cells (DCs). We show that activation of the viral RNA sensors TLR7 and RIG-I in DCs is important for triggering IL-22 secretion by iNKT cells, whereas the NOD-like receptors NOD2 and NLRP3 are dispensable. Invariant NKT cells respond to IL-1β and IL-23 provided by infected DCs independently of the CD1d molecule to release IL-22. In vitro, IL-22 protects IAV-infected airway epithelial cells against mortality but has no role on viral replication. Finally, during early IAV infection, IL-22 plays a positive role in the control of lung epithelial damages. Overall, IAV infection of DCs activates iNKT cells, providing a rapid source of IL-22 that might be beneficial to preserve the lung epithelium integrity. 相似文献
194.
Paul D. Sniegowski 《Journal of molecular evolution》1995,40(1):94-101
Several recent reports have claimed that adaptive mutants in bacteria and yeast are induced by selective conditions. The results of these reports suggest that mutants can arise nonrandomly with respect to fitness, contrary to what has been widely accepted. In several cases that have received careful experimental reexamination, however, the detection of seemingly nonrandom mutation has been explained as an experimental artifact. In the remaining cases, there is no evidence to suggest that cells have the capacity to direct or choose which genetic variants will arise. Instead, current models propose processes by which genetic variants persist as mutations only if they enable cell growth and DNA replication. Most of these models are apparently contradicted by experimental data. One model, the hypermutable state model, has recently received limited circumstantial support. However, in this model the origin of adaptive mutants is random; the apparent nonrandomness of mutation is merely a consequence of natural selection. The critical distinction between the origin of genetic variation (mutation) and the possible consequence of that variation (selection) has been neglected by proponents of directed mutation. 相似文献
195.
Soil CO2 flux was measured across 947 plots at 7 experimentalgrassland sites at the Cedar Creek Natural History Area in order to determinethe relationships between soil CO2 flux and environmental factors,living plant biomass, and soil C and N. Soil CO2 flux increased asthe day progressed, and was positively related to aboveground biomass,belowground biomass, and soil % C. However, most of the variation in soilCO2 flux explained by a multiple regression model(r
2 = 0.55) was attributed to the different experimental sites (61%).Soil CO2 flux increased with increasing aboveground plant biomass(explaining 16% of the model variation),belowground plant biomass (12%), and soil C and C:N ratio(6%). The length of time between aboveground biomass in aplot was clipped and soil CO2 flux variedamong plots. Soil CO2 flux declined with increased timesince clipping, supporting the idea that recently fixedcarbon is a significant component of soil CO2 flux.Soil CO2 flux did not follow standard Q10relationships. Over a 20 °C temperature range,soil CO2 flux tended to be lower in warmer plots.More work is necessary to understand what factors explainthe large differences that were seen among experimentalsites in soil CO2 flux that could not be explainedby biomass or soil properties. 相似文献
196.
197.
A characteristic electric organ discharge display in social encounters between mormyrid fish is a temporary discharge cessation. Using this response, we have investigated the useful range of electrocommunication under different water conductivity conditions in the mormyrid Brienomyrus niger. An individual fish was confined to a porous ceramic shelter tube and moved from a starting distance of 380 cm toward a similarly confined conspecific until discharge, cessation occurred. The moved fish was subsequently returned to its original, position. Water conductivity affects the peak-to-peak source voltage of the electric organ and the sensitivity of the fish's electroreceptors. Within a range of 10 to 36 000 μS/cm, the peak-to-peak amplitude of the electric organ discharge declined as a power function. At 120 μS/cm, the amplitude was 50%, and at 300μS/cm, 30% of the 10 μS/cm value. The interfish distance at which discharge cessation occurred and the associated electric field gradients were dependent on water conductivity and upon the spatial orientation of the two fish (end-to-end or parallel orientations of their shelter tubes). The respective ranges were from 135 cm and 0.02 mV/cm at 52 μS/cm (parallel orientation) to 22 cm and 0.36 mV/cm at 678 μS/cm (end-to-end orientation). When the data for both tube orientations were combined, the relationship between water conductivity (x) and the distance at which discharge cessation occurred (y) could be expressed by a power function, y=K·xa (with K=102.97 and a=?0.56). When an electrically ‘silent’ fish was moved away from its conspecific, a discharge resumption in the form of a high-frequency rebound occasionally effected changes in the other fish's discharge activity at distances up to 157 cm (with an associated electric, field gradient of 0.01 mV/cm under the lowest conductivity condition). 相似文献
198.
199.
Sten Iwarson 《FEMS microbiology reviews》1994,14(3):201-204
Abstract: In 1988, investigators from the Chiron Company (USA) detected the non-A, non-B agent and named it hepatitis C virus (HCV). An anti-HCV antibody assay (ELISA) and subsequently confirmation tests (immunoblot and polymerase chain reaction) were developed. HCV exposure results in a chronic infection in a majority of cases. This chronic infection is associated with slowly progressive chronic liver disease. Chronic HCV infection is, like HBV, also associated with the development of hepatocellular carcinoma. Most HCV carriers are infected by parenteral routes. Intravenous drug users have the highest risk of becoming infected. Intrafamiliar spread is seen in certain parts of the world but sexual and perinatal transmission does not play an important role in spreading the infection. Antiviral therapy (alpha-interferon) in patients with chronic hepatitis C will normalize liver function tests in about 25% of the cases. 相似文献
200.