The acylation and phosphorylation pattern of lipid A from Xanthomonas campestris strongly influence its ability to trigger the innate immune response in Arabidopsis

Lipopolysaccharides (LPSs) are major components of the cell surface of Gram-negative bacteria. LPSs comprise a hydrophilic heteropolysaccharide (formed by the core oligosaccharide and the O-specific polysaccharide) that is covalently linked to the glycolipid moiety lipid A, which anchors these macromolecules to the external membrane. LPSs are one of a group of molecules called pathogen-associated molecular patterns (PAMPs) that are indispensable for bacterial growth and viability, and act to trigger innate defense responses in eukaryotes. We have previously shown that LPS from the plant pathogen Xanthomonas campestris pv. campestris (Xcc) can elicit defense responses in the model plant Arabidopsis thaliana. Here we have extended these studies by analysis of the structure and biological activity of LPS from a nonpathogenic Xcc mutant, strain 8530. We show that this Xcc strain is defective in core completion and introduces significant modification in the lipid A region, which involves the degree of acylation and nonstoichiometric substitution of the phosphate groups with phosphoethanolamine. Lipid A that was isolated from Xcc strain 8530 did not have the ability to induce the defense-related gene PR1 in Arabidopsis, or to prevent the hypersensitive response (HR) that is caused by avirulent bacteria as the lipid A from the wild-type could. This suggests that Xcc has the capacity to modify the structure of the lipid A to reduce its activity as a PAMP. We speculate that such effects might occur in wild-type bacteria that are exposed to stresses such as those that might be encountered during plant colonization and disease.     

携氧剂(正十二烷)对黄原胶发酵的影响

黄原胶(XanthanGum)是由野油菜黄单胞菌(Xanthomonascampestris)以碳水化合物为主要底物,经发酵产生的一种酸性胞外杂多糖。其发酵中后期黏度增大,氧的溶解能力下降,从而影响了黄原胶的产量。研究黄原胶生物合成过程中,烷烃对提高供氧、提高产胶率的影响,同时电镜观察不同发酵时期野油菜黄单胞菌的产胶情况。试验结果表明:8%为最适正十二烷添加量,产胶率达4.16%而对照样仅为2.15%。     

野油菜黄单胞菌xanA基因与pUCm-T载体的连接

本文研究了两种不同的连接方法在野油菜黄单胞菌（Xanthomonas campestris）xanA基因与pUCm-T载体连接中的连接效果,并进行了转化实验进行鉴定.实验结果表明,xanA基因与pUCm-T载体的适宜连接条件为16℃连接过夜.连接体系中,xanA基因与pUCm-T载体的体积比为4：1.     

携氧剂(H2O2)对野油菜黄单胞菌合成黄原胶的影响

黄原胶(Xanthan Gum)是由野油菜黄单胞菌(Xanthomonas campestris)碳水化合物为主要底物，经发酵产生的‘种酸性胞外杂多糖。发酵中后期黏度增大，氧的传质能力下降，从而影响了黄原胶的产量。本课题研究黄原胶生物合成过程中，H2O2对供氧和提高产胶率的影响。根据添加H2O2实验得出，H2O2添加量为1ml即在发酵液中浓度为4．4mmol／L左右为最适的添加量，最佳添加时刻为48h左右。得出低浓度的H2O2能提高黄原胶的产量，产胶率平均提高了3．28％。     

In Vitro Determination of the Antifungal Activity of Artemisia campestris Essential Oil from Algeria

The chemical composition of the essential oil isolated from the aerial parts of Artemisia campestris from Algeria and its antifungal activity against 10 filamentous fungal strains were investigated. The A. campestris essential oil was obtained in a yield of 0.71% (v/w). The major constituents of the oil were α-pinene (18.65%), β-pinene (16.78%), β-myrcene (17.34%), and germacrene D (10.34%). Our study showed that A. campestris essential oil was a potent antifungal agent against some pathogenic fungal species. Fusarium graminearum was the most sensitive strain to A. campestris essential oil with minimal inhibitory concentration and minimal fungicidal concentration values of 1.25 µL/mL (v/v). The essential oil also exhibited a strong fungicidal activity against the tested fungi, except for Penicillium citrinum, P. viridicatum, and Aspergillus niger (MFC >20 µL/mL). Our findings suggested the application of A. campestris essential oil as a biofungicide in order to reduce the dependence on synthetic fungicides and ensure food safety and quality.     

超微粉碎技术对油菜花粉中槲皮素和山奈素溶出率的影响

为了探讨超微粉碎技术对油菜花粉中有效成分(槲皮素和山奈素)溶出的影响,采用高效液相色谱法分析比较油菜花粉超微粉与普通粉(65～100 目)中槲皮素和山奈素的溶出差异。结果表明,油菜花粉超微粉中槲皮素和山奈素的溶出率比普通粉分别提高了45.16% 和27.86%,超微粉碎可显著提高油菜花粉有效成分的溶出率。     

产高黏性黄原胶基因工程菌株的构建

目的获得产高黏度黄原胶基因工程菌株。方法利用PCR技术,以野油菜黄单胞菌X58基因组为模板扩增得到产胶基因gumBC,通过纯化、内切酶酶切、连接和接合,构建了含gumBC基因表达载体(pBBR-gumBC)的重组菌株X58-BC。结果经10 L发酵罐实验证实,gumBC过量表达,黄原胶黏度值(Brookfield s05,60 r/min)提高了62%,剪切性能值提高了57%。结论成功构建了产高黏度黄原胶基因工程菌株。     

Molecular cloning and characterisation of cytoplasmic glutamine synthetase gene BcGS1 from non‐heading Chinese cabbage

BACKGROUND: Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of nitrogen (N) assimilation, catalysing the synthesis of glutamine from ammonium and glutamate. Plants have two types of GS isoenzyme that are localised in different compartments: one in the cytosol (GS1) and the other in the chloroplast (GS2). GS1 is the major form of GS in plant roots and directly converts ammonium taken up by plant roots to glutamine. RESULTS: The GS1 gene cDNA of non‐heading Chinese cabbage (Brassica campestrisssp. chinensis Makino) cultivar ‘Suzhouqing’ was isolated by RT‐PCR (real‐time polymerase chain reaction) and (5′/3′)‐RACE (rapid amplification of cDNA ends) techniques. It was classified as GS1 by sequence alignment and motif search and named B. campestris ssp. chinensis Makino GS1 (BcGS1). Subcellular localisation analysis showed that BcGS1 was distributed in the cytoplasm of cells. BcGS1 was expressed in all parts, but mainly in the roots, which was verified by northern blotting analysis. Additionally, its expression was influenced by the N source concentration. CONCLUSION: These results suggest that BcGS1 is a novel member of the GS family in plants. BcGS1 was significantly related to N assimilation in non‐heading Chinese cabbage, demonstrating that this gene plays an important role in plant growth and development. Copyright © 2010 Society of Chemical Industry     

黄原胶发酵工艺条件的优化研究

目的优化黄原胶的发酵工艺以提高黄原胶的产量及黏度。方法采用摇瓶发酵,改变实验条件,包括培养基中碳源、氮源的种类和浓度,复合氮源的组成及含量,无机盐的组成及含量,柠檬酸和碳酸钙的含量等。通过测定发酵液黏度、粗胶含量来确定较为适合的发酵工艺。结果通过实验得到最佳培养基组成为:蔗糖4%,硫酸铵0.1%,豆饼粉0.3%,柠檬酸0.1%,硫酸镁0.01%,碳酸钙0.02%;培养条件为:500 mL摇瓶发酵装液量100 mL,转速220 r/min,发酵温度28.5℃,培养72h。进行了发酵罐发酵实验,黄原胶的发酵产量可以达到25.02g/L,发酵液的终黏度5847cP。结论通过工艺优化,黄原胶产量及黏度均得到提高。