Construction and analysis of a Mannheimia haemolytica A1 luxS mutant

Mannheimia haemolytica A1 is the causative agent of bovine pneumonic pasteurellosis, a major cause of sickness, death, and economic loss to the feedlot cattle industry. M. haemolytica A1 produces autoinducer-2 (AI-2) like molecules that are capable of inducing quorum sensing system 2 of Vibrio harveyi. This interspecies quorum sensing system has been shown to regulate the expression of virulence genes in several pathogenic bacteria. The protein central to the production of AI-2 is LuxS. To determine if quorum sensing is involved in the regulation of virulence genes in M. haemolytica A1, a luxS mutant was constructed by replacing luxS with a cat cassette. This mutant was verified by PCR analysis, Southern hybridization, as well as its inability to induce bioluminescence in the V. harveyi reporter strain. RT-PCR analysis showed there was no difference in leukotoxin (lktC) mRNA levels, however there were increased mRNA levels of putative virulence associated genes, transferrin binding protein B (tbpB), adhesin (ahs) and capsule biosynthesis (nmaA). Electron microscopy showed that the level of encapsulation in the mutant is higher than the parent. Additionally, the mutant was slightly more adherent to bovine tracheal cells than the parent. In vitro competition assays showed the mutant out-competed the parent under iron-restricted conditions. However, in a calf challenge, the parent was the dominant isolate recovered.     

Determination of the antibiotic fungicide validamycin A in formulated products by micellar electrokinetic chromatography.

A micellar electrokinetic capillary chromatographic method (MEKC) was used to determine validamycin A content in commercial products. The results indicated that this method was capable of analyzing the validamycin A content in formulated products with an instrument detection limit of 0.94 microg/mL and a method detection limit of 1. 70 microg/mL. Relative standard deviation (RSD) values of MEKC determination of validamycin A in formulated products ranged from 0. 61 to 2.09%. Recoveries of validamycin A in formulated products were in the region of 99.5-105.1%. All commercial products collected from markets contained validamycin A. The high percentage of recovery, the low detection limit, and the low RSD values confirmed that the MEKC technique is a senstivie and selective method.     

S9606菌发酵脱毒棉籽粕饲喂蛋鸡

饲料中添加６．５％～１０％的含游离棉酚为０．０１０１％～０．０１６４％的发酵脱毒棉粕,鸡的产蛋率提高０．０３％～４．０３％。其中添加７．６６％的发酵脱毒棉粕的饲料,其经济效益最好,１０００ｇ蛋成本降低０．１７３２元、料蛋比由２．６２８７降到２．５２５０。试验组和对照组的鸡血清谷雨转氨酶活性、总蛋白含量、清蛋白和球蛋白的相对含量、清蛋白和球蛋白之比均差异不显著。说明饲喂脱毒棉粕的鸡,其肝脏和其他组织的功能正常、健康。     

Cross-scale effects of land use on the functional composition of herbivorous insect communities

Landscape Ecology - Insect herbivores comprise the majority of macroinvertebrate communities of temperate grasslands and act as drivers for important ecosystem functions. Landscape- and local-level...     

柑桔种子的热处理试验

各种柑桔类的种子经热水或湿热空气54～56℃处理10～60分钟,有的甚至经57℃处理50分钟后播种,其发芽率及长出的幼苗的生长一般均不受影响。某些品种的种子经适当的温度和时间处理后,其发芽率显著提高。看来,一般柑桔类种子经56℃温汤处理50分钟是安全的。采用这温度和时间处理柑桔类种子可以消除种子内可能带有的黄龙病、斑黄病的病原体和溃疡病、疮痂病等病原菌。柑桔类种子经过热处理的如同不经热处理的一样,可以短期贮藏不致表失发芽力。     

洋麻炭疽病(Colletotrichum hibisci Pollacci)的防治研究

 洋麻炭疽病早在1912年即于台湾发現,以后传到內地,按其引种的来源分析,是自印度传入中国的。