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151.
The catalase-peroxidase gene and isoniazid resistance of Mycobacterium tuberculosis. 总被引:82,自引:0,他引:82
Tuberculosis is responsible for one in four of all avoidable adult deaths in developing countries. Increased frequency and accelerated fatality of the disease among individuals infected with human immunodeficiency virus has raised worldwide concern that control programmes may be inadequate, and the emergence of multidrug-resistant strains of Mycobacterium tuberculosis has resulted in several recent fatal outbreaks in the United States. Isonicotinic acid hydrazide (isoniazid, INH) forms the core of antituberculosis regimens; however, clinical isolates that are resistant to INH show reduced catalase activity and a relative lack of virulence in guinea-pigs. Here we use mycobacterial genetics to study the molecular basis of INH resistance. A single M. tuberculosis gene, katG, encoding both catalase and peroxidase, restored sensitivity to INH in a resistant mutant of Mycobacterium smegmatis, and conferred INH susceptibility in some strains of Escherichia coli. Deletion of katG from the chromosome was associated with INH resistance in two patient isolates of M. tuberculosis. 相似文献
152.
The diatom flora of the Oregon Caves National Monument, Josephine Co., Oregon, was investigated. Diatoms were distributed throughout the cave system with abundance and species diversity depending upon moisture, light, availability of mineral nutrients, and proximity to cave openings. Twenty-six taxa were identified and described. 相似文献
153.
Douglas-fir beetle ( Dendroctonus pseudotsugae Hopk.) infestations frequently result from disturbance events that create large volumes of weakened Douglas-fir trees, Pseudotsuga menziesii (Mirb.) Franco. Previous research has focused on determining susceptibility of forest stands to Douglas-fir beetle and predicting the amount of tree mortality from Douglas-fir beetle infestations following disturbance events. Little work has been done on consequent changes in the forest overstory and understory. In the early 1990s, populations of Douglas-fir beetle increased in fire-scorched trees, subsequently infesting undamaged neighboring stands in the Rocky Mountains of western Wyoming, USA. In 1999 transect sampling and 25 pairs of previously infested and uninfested plots were used to quantify changes in forest stand conditions and ensuing responses in the understory caused by Douglas-fir beetle infestations. Significant effects of the Douglas-fir beetle infestation comprised 3 general categories: (1) overstory effects: basal area was reduced by 40%-70%, average tree diameter decreased by 8%-40%, and the Douglas-fir component of the overstory decreased by more than 12%; (2) regeneration effects: conifer seedling regeneration increased nearly fourfold in infested plots and 90% of the regeneration was Douglas-fir; (3) understory effects: understory vegetation (forbs, grass, and shrubs) had a threefold increase in infested compared with uninfested plots. In addition, basal area of Douglas-fir killed by the Douglas-fir beetle was significantly correlated with initial Douglas-fir basal area and percentage of Douglas-fir, but not with stand density index, tree diameter, or trees per hectare. Significant inverse relationships also were found between post-infestation basal area and abundance of forbs, grass, and shrubs, and understory height. Thus, we found that Douglas-fir beetle infestations cause significant short-term effects in both the overstory and understory and contribute to an altered mosaic in forest structure. 相似文献
154.
Okanagana striatipes and O. utahensis are species synchronous in location of activity and utilization of host plants. They possess similar acoustic behavior. Analysis of calling songs shows that calls overlap in frequency but differ in temporal pattern. Based on characteristics of the cicada auditory system and the species recognition mechanism, the potential for acoustic interference exists. Both species are ectothermic behavioral thermoregulators. Measurements of thermal preference and body temperature during singing show that although thermal preferences are similar, O. utahensis sings at a significantly higher body temperature. Differences in body temperature required to coordinate singing in the 2 species provide a partial temporal separation of acoustic signaling. We suggest the physiological mechanisms that permit synchronous utilization of a habitat by the 2 species are the production of calling songs of different temporal patterns and the presence of different thermal requirements, which may permit and/or facilitate temporal separation of the acoustic environment during the day. 相似文献
155.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Collections of mayflies of the Leptophlebiidae, genera Choroterpes Eaton, Paraleptophlebia Lestage, Thraulodes Ulmer, and Traverella Edmunds from the southwestern United States and northwestern Mexico are reviewed. Choroterpes (Choroterpes) oaxacaensis Brusca & Allen is synonymized with C. (C.) inornata Eaton. The nymph described as Thraulodes species “D” Allen & Brusca is the nymph of T. arizonicus McDunnough. New distributional records extend the known ranges of C. inornata, C. (Neochoroterpes) mexicanus Allen, Paraleptophlebia memorialis (Eaton), T. arizonicus, T. brunneus Koss, T. salinus Kilgore & Allen, T. speciosus Traver, Traverella albertana (McDunnough), and T. castanea Kilgore & Allen. 相似文献
156.
Mima moundfields were investigated at the Lawrence Memorial Grassland Preserve, located on the Columbia Plateau in southern Wasco County, Oregon, and at three locations in the San Luis Valley and Sangre de Cristo Mountains, southern Colorado, to test the alternative hypotheses of mound origins by erosion, frost action, and soil translocation by geomyid pocket gophers. The concentrations of two size classes of small stones, gravel (8-15 mm diameter) and pebbles (15-50 mm diameter), were sampled along mound-to-intermound transects and at different depths within the mounds. Numbers and masses of small stones per unit soil volume increased from intermounds to mounds tops at the Colorado sites and from mound edge to mound top at the Oregon site, where thin intermound soils lay directly on the weathering surface of basalt bedrock. Numbers and masses of small stones in the surface soil of mound tops were greater than or similar to concentrations in deeper layers. Mean masses of individual pebbles were greater in the intermound zone than in mound soils at the Oregon site, but did not differ along mound-intermound gradient at the Oregon site and at one Colorado site, being highest at mound edges or in intermounds. These observations support the hypothesis that mounds are formed by centripetal translocation of soil by geomyid pocket gophers, and are contrary to predictions based on theories assuming erosion or frost action to be the mechanism of mound formation. 相似文献
157.
Between 1983 and 1985, 97 mottled sculpin, Cottus bairdi Girard, were examined from five collection sites in central Utah for parasites. Eight different species of parasites were observed, representing seven genera of Protozoa ( Plistophora, Myxidium, Myxobolus, Ichthyophthirius, Trichodina, Apiosoma, Eimeria ) and one genus of Nematoda ( Rhabdochona ). The highest number of parasites was found in sculpin from the Provo River near residential areas, while the lowest number was recorded from Hobble Creek, a nearby pristine area. A complete list of parasites for C. bairdi with literature citations is presented. Each observed parasite is discussed emphasizing pathogenesis to the host. 相似文献
158.
159.
辛浩;韩强;姚小虎 《华南理工大学学报(自然科学版)》2008,36(6)
采用分子动力学方法,分别对含单、双原子空位缺陷的扶手椅形单层碳纳米管及其完善结构进行轴向压缩的数值模拟,对比两种长度纳米管在不同温度条件下的承载性能.模拟结果表明,温度越低、碳纳米管的长度越长,完善纳米管屈曲强度的温度依赖性越显著.管壁缺陷显著降低了纳米管的承载能力,而且含缺陷碳纳米管的屈曲性能对温度变化并不敏感. 相似文献
160.
Cooper JD Smyth DJ Smiles AM Plagnol V Walker NM Allen JE Downes K Barrett JC Healy BC Mychaleckyj JC Warram JH Todd JA 《Nature genetics》2008,40(12):1399-1401
We carried out a meta-analysis of data from three genome-wide association (GWA) studies of type 1 diabetes (T1D), testing 305,090 SNPs in 3,561 T1D cases and 4,646 controls of European ancestry. We obtained further support for 4q27 (IL2-IL21, P = 1.9 x 10(-8)) and, after genotyping an additional 6,225 cases, 6,946 controls and 2,828 families, convincing evidence for four previously unknown and distinct risk loci in chromosome regions 6q15 (BACH2, P = 4.7 x 10(-12)), 10p15 (PRKCQ, P = 3.7 x 10(-9)), 15q24 (CTSH, P = 3.2 x 10(-15)) and 22q13 (C1QTNF6, P = 2.0 x 10(-8)). 相似文献