Identification and Manipulation of Soil Properties To Improve the Biological Control Performance of Phenazine-Producing Pseudomonas fluorescens

Pseudomonas fluorescens 2-79RN₁₀ protects wheat against take-all disease caused by Gaeumannomyces graminis var. tritici; however, the level of protection in the field varies from site to site. Identification of soil factors that exert the greatest influence on disease suppression is essential to improving biocontrol. In order to assess the relative importance of 28 soil properties on take-all suppression, seeds were treated with strain 2-79RN₁₀ (which produces phenazine-1-carboxylate [PCA⁺]) or a series of mutants with PCA⁺ and PCA⁻ phenotypes. Bacterized seeds were planted in 10 soils, representative of the wheat-growing region in the Pacific Northwest. Sixteen soil properties were correlated with disease suppression. Biocontrol activity of PCA⁺ strains was positively correlated with ammonium-nitrogen, percent sand, soil pH, sodium (extractable and soluble), sulfate-sulfur, and zinc. In contrast, biocontrol was negatively correlated with cation-exchange capacity (CEC), exchangeable acidity, iron, manganese, percent clay, percent organic matter (OM), percent silt, total carbon, and total nitrogen. Principal component factor analysis of the 16 soil properties identified a three-component solution that accounted for 87 percent of the variance in disease rating (biocontrol). A model was identified with step-wise regression analysis (R² = 0.96; Cp statistic = 6.17) that included six key soil properties: ammonium-nitrogen, CEC, iron, percent silt, soil pH, and zinc. As predicted by our regression model, the biocontrol activity of 2-79RN₁₀ was improved by amending a soil low in Zn with 50 μg of zinc-EDTA/g of soil. We then investigated the negative correlation of OM with disease suppression and found that addition of OM (as wheat straw) at rates typical of high-OM soils significantly reduced biocontrol activity of 2-79RN₁₀.     

从标准化课件做起,强化教学过程管理,全面提高教学质量

加强课程建设、强化教学过程管理,是保障课堂教学质量,全面提升教育教学水平的关键点之一.近年来,由于学院各教研室教学活动和课程建设开展的情况良莠不齐,集体备课多流于形式,因此,组织开展了“标准化课件制作”的教研活动,通过“标准化课件”这个有形主体的建设,加强教学经验交流、促进青年教师培养、提高课堂教学质量,有效课程建设和教学团队建设.活动中,要求所有教研室开展标准化课件制作,由专家组进行抽查和督导,并配以奖罚机制.经过学院教研室、督导组、管理部门的共同努力,不仅使各教研室具备了基本的紧扣教学大纲、适合教学对象需要、例题典型、教学形式多样的标准化课件;更重要的是在活动中交流教学经验,达到了教研室教学思路统一、教学目标一致,对年轻教师教学传帮带的目的;同时也是针对集体备课的过程管理,规范集体备课.该活动开展的效果较好,有效的督促教研组开展课程建设、教学团队建设,规范教学活动,使教学质量有了进一步提升.     

Use of Random and Saturation Mutageneses To Improve the Properties of Thermus aquaticus Amylomaltase for Efficient Production of Cycloamyloses

Amylomaltase from Thermus aquaticus catalyzes intramolecular transglycosylation of α-1,4 glucans to produce cyclic α-1,4 glucans (cycloamyloses) with degrees of polymerization of 22 and higher. Although the amylomaltase mainly catalyzes the transglycosylation reaction, it also has weak hydrolytic activity, which results in a reduction in the yield of the cycloamyloses. In order to obtain amylomaltase with less hydrolytic activity, random mutagenesis was perfromed for the enzyme gene. Tyr54 (Y54) was identified as the amino acid involved in the hydrolytic activity of the enzyme. When Y54 was replaced with all other amino acids by site-directed mutagenesis, the hydrolytic activities of the mutated enzymes were drastically altered. The hydrolytic activities of the Y54G, Y54P, Y54T, and Y54W mutated enzymes were remarkably reduced compared with that of the wild-type enzyme, while those of the Y54F and Y54K mutated enzymes were similar to that of the wild-type enzyme. Introducing an amino acid replacement at Y54 also significantly affected the cyclization activity of the amylomaltase. The Y54A, Y54L, Y54R, and Y54S mutated enzymes exhibited cyclization activity that was approximately twofold higher than that of the wild-type enzyme. When the Y54G mutated enzyme was employed for cycloamylose production, the yield of cycloamyloses was more than 90%, and there was no decrease until the end of the reaction.