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51.
Leigh Watterworth Bruce Rosa Heidi Schraft Edward Topp Kam Tin Leung 《Water, air, and soil pollution》2006,177(1-4):367-382
Recently, there has been a surge of interest in understanding the survival of Shiga toxin-producing Escherichia coli (STEC) in aquatic environments. Fifteen strains of STEC were monitored, individually, in untreated well water samples incubated at 10 and 22^C for 56 days. The strains were selected from three serogroups (O26, Ol11 and O157) and represented five distinct ERIC (enterobacterial repetitive intergenic concensus)-genotypes. The microcosms were prepared in triplicate and inoculated at an initial cell density of about 7.0 log CFU/ml well water. At 10^C, the cell density of five STEC strains fell below the detection limit of 0.8 log CFU/ml by day 56. Of the ten persisting strains, four showed superior survival with cell densities decreasing to an average of about 5 log CFU/ml while the remaining six strains showed moderate levels of survival, decreasing to an average cell density of about 3 log CFU/ml. At 22^C, strain H32 (genotype I) and H15 (genotype B) persisted at 1.1 log CFU/ml and 2.2 log CFU/ml in 56 days, respectively. The other 13 STEC strains dropped below the detection limit between weeks 3 to 8. The 15 strains demonstrated highly variable levels of survival with no correlation between ERIC-genotypes or serogroups and the strains' ability to persist in the well water samples. Although strain H32 (O157:H7) persisted significantly longer than strain H22 (O157:H7) in natural well water at both 10 and 22^C, both strains survived equally well in sterile well water, indicating that individual STEC strains vary in their ability to compete with background microbial populations. 相似文献
52.
从法氏囊组织分离IBDV超强毒株HK46并提取基因组RNA。以RNA为模板进行反转录合成cDNA第一链。采用长PCR扩增技术获得VP2-4-3 cDNA全长片段。将PCR产物克隆到pcDNA3.1( )载体,得到重组质粒pPP1。对pPP1插入片段全长序列进行了测序并对其序列进行了分析。结果表明,VP2-4-3 cDNA阅读框架由3039bp组成,可编码1012个氨基酸组成的前体多聚蛋白。经比较得知,HK46超强毒株VP2-4-3氨基酸序列与经典毒株间存在19-28个氨基酸的差异;与Harbin强毒株相差32个氨基酸;而与超强毒株OKYM和UK661分别相差2和6个氨基酸,且它们的VP2序列完全相同。在HK46超强毒株所特有的9个氨基酸中,3个位于VP2可变区,显示超强毒株其抗原性存在着变异。 相似文献
53.
鸡生长激素基因内含子4新等位基因的序列分析 总被引:6,自引:2,他引:4
试验以粤黄鸡矮脚黄系等不同肉鸡、蛋鸡品种(系)作为试验材料,对新发现的生长激素基因内含子4等位基因的PCR产物作纯化测序,研究多态性产生的机理及碱基变异情况。结果发现cGH内含子4长约1170bp,内含子4的A、B、C、D等位基因长分别为1170bp、1164bp、1168bp,它们之间存在不同程度的碱基差异,而第580碱基的突变(A→G)和第688碱基的突变(A→G)分别产生了MspⅠ酶切位点,是多态性形成的根本原因。“PCR产物双带”的形成是由于cGH基因内含子4其中一条链上第420-470位碱基全部缺失,不同等位基因间存在碱基缺失、插入和替换,测序结果与酶切后电泳结果相吻合。 相似文献
54.
An erythromycin derivative produced by targeted gene disruption in Saccharopolyspora erythraea 总被引:14,自引:0,他引:14
J M Weber J O Leung S J Swanson K B Idler J B McAlpine 《Science (New York, N.Y.)》1991,252(5002):114-117
Derivatives of erythromycin with modifications at their C-6 position are generally sought for their increased stability at acid pH, which in turn may confer improved pharmacological properties. A recombinant mutant of the erythromycin-producing bacterium, Saccharopolyspora erythraea, produced an erythromycin derivative, 6-deoxyerythromycin A, that could not be obtained readily by chemical synthesis. This product resulted from targeted disruption of the gene, designated eryF (systematic nomenclature, CYP107), that apparently codes for the cytochrome P450, 6-deoxyerythronolide B (DEB) hydroxylase, which converts DEB to erythronolide B (EB). Enzymes normally acting on EB can process the alternative substrate DEB to form the biologically active erythromycin derivative lacking the C-6 hydroxyl group. 相似文献
55.
Although studies have been performed to test whether conjugated linoleic acid (CLA) acts as an antioxidant, the results were not conclusive. In addition, the CLA widely used in previous research contains 43% cis-9,trans-11 isomer, 45% trans-10,cis-12 isomer, and 10 other minor isomers. The objective of this study was to investigate the antioxidant activity of cis-9,trans-11- and trans-10, cis-12-CLA isomers using high-purity CLA isomers (>98%) by total oxyradical scavenging capacity assay (Winston, G. W.; Regoli, F.; Dugas, Jr., A. J.; Fong, J. H.; Blanchard, K. A. Free Radical Biol. Med. 1998, 24, 480-493). At all concentrations (2-200 microM), t10, c12-CLA performed as an antioxidant with a 15-min lag phase, which was more effective than c9,t11-CLA and alpha-tocopherol at lower concentrations (2 and 20 microM). On the other hand, c9,t11-CLA possessed weak antioxidant activity at 2 and 20 microM, whereas at 200 microM it acted as a strong pro-oxidant, which suggests that discrepancies of the results of the previous studies on the antioxidant properties of CLA may be due to the balance of the antioxidant properties of t10,c12-CLA and the pro-oxidant properties of c9,t11-CLA in different oxidation conditions. 相似文献
56.
Bith‐Hong Ling Pingsun Leung Yung C. Shang 《Aquaculture Economics & Management (Blackwell Science)》2013,17(3):119-128
Abstract This study analyses the behaviour of the price transmission process for the leading cultured shrimp species, black tiger shrimp (Penaeus monodon), in both forward and backward directions between Thai and Indonesian shrimp packer markets and the Japan Tokyo wholesale market. The bivariate cointegration approach using the Engle‐Granger two‐stage estimation procedure is applied in this study. The results show that Tokyo wholesale prices appear to have stronger backward influences on the formation of overseas contract prices used by Japanese shrimp importers in the Thai and Indonesian shrimp packer markets. In addition, there is a tendency for the speed of price transmissions in the long term to increase with increasing size class (from 26 to 30–21–25 and 16–20 counts per pound) of black tiger shrimp, regardless of estimation specification in the direction of price transmissions and the shrimp country of origin. 相似文献
57.
58.
59.
Jiang Meng Kelvin Sze-Yin Leung Xiao-ping Dong Yi-sheng Zhou Zhi-hong Jiang Zhong-zhen Zhao 《Fitoterapia》2009,80(8):468-474
An on-line high performance liquid chromatography (HPLC)–diode array detector (DAD)–electrospray ionization mass spectrometry (ESI–MS) method has been developed to quantify simultaneously eight bioactive chemical components in Houttuynia cordata Thunb and related Saururaceae medicinal plants. Simultaneous separation of these eight compounds was achieved on a C18 analytical column with gradient elution of acetonitrile and 0.2% acetic acid (v/v) at a flow rate of 0.6 mL/min and being detected at 280 nm. These eight compounds were completely separated within 90 min. Good linear regression relationship (r2 > 0.9978) within test ranges was shown in all calibration curves. Good repeatabilty for the quantification of these eight compounds in H. cordata was also demonstrated in this method, with intra- and inter-day variations less than 3.0%. The method established was successfully applied to quantify eight bioactive compounds in closely related species of H. cordata, which provides a new basis for quality assessment of H. cordata. 相似文献
60.
Sai Leung Ng Qiang Guo Cai Shu Wan Ding Kwai Cheong Chau Jie Qin 《Agroforestry Systems》2008,74(3):279-291
Soil erosion has long been recognized as a major environmental problem in the Three Gorges Region (TGR) where slope farming
is commonly practiced but the local topography is hilly. In consideration of the poor socioeconomic position of local farmers,
low cost hedgerows had been introduced as a soil conservation measure to the TGR in the late 1980s. A collaborative research
programme was initiated by the Chinese University of Hong Kong, the Chinese Academy of Science, the Huazhong Agricultural
University, and the Bureau of Soil and Water Conservation of Zigui County to study the potential of adopting hedgerows in
the TGR. Six experimental plots (10 m × 2 m, gradient = 25°) were constructed at Zigui County, Hubei Province to study effects
of hedgerows on erosion, nutrient loss and crop productivity. Results indicated that there were significant relationships
between rainfall and runoff, and rainfall and soil loss, respectively. Conventional slope farming could not be considered
a sustainable agricultural practice because it resulted in severe erosion and low crop yield. Hedgerows per se seemed not
to be effective in reducing soil loss and boosting crop productivity, but performances could be greatly improved when they
combined with the use of fertilizers. Current farming and fertilization practices, however, generally did not meet N demands
of crops. Results and findings of this paper will contribute towards a technical reference for the promotion and adoption
of hedgerows in the TGR. 相似文献