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61.
Experiments were conducted to compare the growth and growth compensation of three strains of juvenile Oreochromis niloticus . Ten full sib families (10 replicates) per strain were split and grown under crowded and uncrowded conditions for 3 weeks (the treatment). Both treatments were then grown an additional 12 weeks under less crowded conditions (the compensation). Standard length measurements were made at the end of crowding and the end of compensation. Each replicate included a size-matched control population of a fourth (red) reference strain. ANCOVA with the reference strain used as a cofactor revealed significant strain effects on specific growth throughout the experiment. The reference strain removed most of the random among-replicate error variance as shown by an increase of r 2 from 0.06 to 0.91 when it was included in the statistical models. If the reference fish had not been used, approximately 450 replicate families would have been needed to achieve the sensitivity of the present experiment (a difference of 7% among strains significant at P =0.05). We conclude that the CLSU strain grows significantly more slowly than the Israel and NIFI strains under the experimental conditions, that the crowding effect was essentially eliminated after 12 weeks of compensation, and that the reference strain greatly improved the resolution of the strain-testing experiment. 相似文献
62.
63.
Tonia S. Agin J. Robert Cantey Edgar C. Boedeker Marcia K. Wolf 《FEMS microbiology letters》1996,144(2-3):249-258
Abstract A number of enteric pathogens, including enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli , Hafnia alvei , a strain of Citrobacter freundii , and rabbit EPEC strain RDEC-1 cause attaching-effacing (AE) lesions in the gut mucosa. These bacteria have a pathogenicity cassette (locus of enterocyte effacement or LEE) containing the eaeA gene. This gene encodes intimin, an outer membrane protein required for production of AE lesions. RDEC-1, a non-invasive enteropathogen in young rabbits, produces AE lesions morphologically indistinguishable from lesions caused by human AE bacterial strains. The RDEC-1 example of E. coli diarrhea in rabbits is an important model for studying the pathogenesis of AE bacteria in a natural infection and for analyzing specific roles of the components of LEE. In order to better understand the role of intimin in the development of AE lesions, a portion of DNA within RDEC-1 LEE, containing the eaeA gene and an upstream open reading frame (ORF), was sequenced. The RDEC-1 eaeA gene shared 87%, 92%, and 93% DNA sequence identity and > 80% amino acid sequence identity with the eaeA genes of C. freundii biotype 4280, EHEC O157:H7, and EPEC O127:H6, respectively. The carboxy-terminal 280 amino acid residues of intimin has 80%, 56%, and 54% identity with C. freundii , EHEC O157:H7, and EPEC O127:H6 intimins, respectively. The predicted protein encoded by the upstream ORF (156 amino acids) shares 95%, 97%, and 99% amino acid identity with predicted proteins from C. freundii , EHEC O157:H7, and EPEC O127:H6, respectively. The high degree of sequence homology of the ORF and the eaeA gene of RDEC-1 with those of other AE bacteria suggests an evolutionary relationship of LEE and supports and facilitates the use of the RDEC-1 model for studying the role of LEE in pathogenesis. 相似文献
64.
Hydroxynitrile lyases: Functions and properties 总被引:6,自引:0,他引:6
Plant hydroxynitrile lyases (Hnl) have attracted the attention of bioorganic scientists for more than 90 years. However, the most important increase in knowledge of this class of enzymes has only arisen in the recent decade. The industrial application of these enzymes as biocatalysts for the synthesis of enantiomerically pure α-cyanohydrins may be responsible for the growing interest in this area.
The Hnls are involved in the catabolic degradation of cyanogenic glycosides, releasing HCN which serves as defense agent against herbivores and microbial attack, or as a nitrogen source. Hydroxynitrile lyases from various plant families appear to represent a new example of enzymes that originated from the convergent evolution of different precursor proteins. The enzymes have been classified into non-FAD- and FAD-containing proteins. FAD-containing enzymes have been isolated exclusively from the Rosaceae, whereas the FAD-independent Hnls, which are more heterogenous in structure, have been characterized from various plant families (Poaceae, Euphorbiaceae, Linaceae, Olacaceae. Filitaceae). The aim of this review is to present a general survey of the natural function and localization of this class of enzymes and a comprehensive summary of the biochemical and genetic data of the isolated proteins. 相似文献
The Hnls are involved in the catabolic degradation of cyanogenic glycosides, releasing HCN which serves as defense agent against herbivores and microbial attack, or as a nitrogen source. Hydroxynitrile lyases from various plant families appear to represent a new example of enzymes that originated from the convergent evolution of different precursor proteins. The enzymes have been classified into non-FAD- and FAD-containing proteins. FAD-containing enzymes have been isolated exclusively from the Rosaceae, whereas the FAD-independent Hnls, which are more heterogenous in structure, have been characterized from various plant families (Poaceae, Euphorbiaceae, Linaceae, Olacaceae. Filitaceae). The aim of this review is to present a general survey of the natural function and localization of this class of enzymes and a comprehensive summary of the biochemical and genetic data of the isolated proteins. 相似文献
65.
Summary During the growth of Kluyveromyces marxianus var. marxianus ATCC 10022 on lactose, peaks of glucose, but not -galactosidase activity, were detected iroculture medium. Harvested and washed whole cells produced glucose and galactose from lactose, or ortho-nitro-phenol from the chromogenic substrate ortho-nitro-phenyl--D-galactopyranoside (ONPG), indicating that -galactosidase is physically associated with cells. ONPG hydrolysis by whole cells presented a monophasic kinetics (Km 36.6 mM) in lactose exponential growth phase cells, but a biphasic kinetics (Km 0.2 and 36.6 mM) in stationary growth phase cells. Permeabilization with digitonin or disruption of cells from both growth phases led to monosite ONPG hydrolysis (Km 2.2 to 2.5 mM), indicating that =galactosidase is not located in the periplasm. In addition, the energy inhibitors fluoride or arsenate, as well as the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) prevented ONPG hydrolysis by whole cells. These findings indicate that energy coupled transmembrane transport is the rate-limiting step for intracellular ONPG cleavage. The taxonomic and physiologic implications of the exclusive intracellular location of -galactosidase of K. marxianus var. marxianus ATCC 10022 are discussed. 相似文献
66.
N J SPENCE A. MEAD A. MILLER E D SHAW D G A WALKEY 《The Annals of applied biology》1996,129(2):247-259
The effects on yield in courgette and marrow (Cucurbita pepo) crops resulting from inoculation with the mild strain of zucchini yellow mosaic virus (ZYMV:WK), have been determined in polythene-house trials and in three years of outdoor, commercial field trials. In polythene-house trials ZYMV:WK inoculated plants were up to 10 days later in flowering than uninoculated plants and their cumulative yields were between 5% and 26% less than uninoculated plants depending on the cultivar. In most field trials cumulative yields from inoculated plants were between 4% and 38% less than uninoculated plants depending on the site and cultivar, but in one trial the yield was 7% higher from inoculated plants. In all experiments, courgette and marrow fruits harvested from ZYMV:WK inoculated plants were symptomless and indistinguishable from fruit harvested from uninoculated plants. The mild leaf symptoms induced by ZYMV:WK infection did not intensify to severe leaf symptoms and where there were natural outbreaks of severe ZYMV infection, fruits from inoculated plants remained symptomless whilst those from uninoculated plants were severely affected and unmarketable. 相似文献
67.
A组轮状病毒SA11VP6基因的克隆和表达 总被引:4,自引:0,他引:4
从SA11VP6基因全序列克隆开始,设计一对两端带有酶切位点的引物,逆转录PCR扩增出VP6全基因CDNA。经酶切后插入PUC19,构建了VP6全基因克隆PRA6。再经酶切后插入痘苗病毒载休质凿PJSA1175中。利用Lipofectin导入TK143细胞,利用TK基因和Lac基因作为重组病毒的筛选标记。表达产物用单克隆抗体ELISA法检测,发现细胞培养上清和细胞裂解液都是阳性。Western b 相似文献
68.
棉铃虫致病菌BT—931菌株的应用研究 总被引:1,自引:0,他引:1
1992-1993年,作者从菏泽、聊城棉田采集的自然罹病死亡棉铃虫幼虫体内,分离到2个较高毒效的Bt菌株,编号为BT—931和BT—021,经室内毒力测定和田间药效试验表明,防效及保蕾效果接近或超过化学农药,菌药混剂3—5天平均防治效果达87.0-91.6%,增效作用显著。经1994年大田防治示范表明,利用BT—931菌剂。配合化学农药防治棉铃虫,具有成本低、保护天敌、持效期长、增产效益高等优点。本研究对菌剂的田间应用技术进行了试验示范。 相似文献
69.
The heterobasidiomycetous yeastRhodotorula glutinis was able to grow in medium containing a high concentration of LiCl. This character ofR. glutinis was presumed to be attributable to its ability to incorporate [14C]-adenine and [14C]-leucine into nucleic acids and proteins, respectively, in the presence of LiCl. Intracellular levels of Li+ and Cl– ions, production and accumulation of glycerol as an osmoregulator, and respiration in the LiCl-stressed condition were almost the same in the tolerant yeastR. glutinis and the sensitive yeastRhodosporidium sphaerocarpum. 相似文献
70.
A new simple method for the preparation of chemically crosslinked chitosan beads is presented. It consists of the dropwise addition of 2-3% (w/v) low molecular weight chitosan solution containing 2% (w/v) glyoxal in 1% (w/v) tetrasodiumdiphosphate, pH 8.0. Immobilized viable baker's yeast (Saccharomyces cerevisiae) could be obtained via gel entrapment within the new beads when means preventing their direct contact with soluble chitosan were provided, "disguising" the cells until gelation and crosslinking were completed. Such means included cell suspension in castor oil or mixing with carboxymethyl-cellulose powder. Application of these means was shown to be necessary, as cells exposed to soluble chitosan immediately lost their viability and glycolytic activity. Yeast disguised in castor oil was also protected from bead reinforcement by glutaraldehyde treatment, significantly strengthening bead stability while operating under acidic conditions. This capability was demonstrated by continuous ethanol production by chitosan entrapped yeast. (c) 1994 John Wiley & Sons, Inc. 相似文献