纺锤芽孢杆菌(Bacillus fusiformis)降解萘的特性及动力学

在前期研究中发现,纺锤芽孢杆菌(Bacillus fusiformis,BFN)可以用于降解水溶液的萘,为了解其降解过程,发现BFN菌生长量随着溶液中的萘的含量增加而提高。其中,萘的含量分别是30、50、100和200 mg/L时,BFN的生物量OD600值分别为0.057、0.081、0.126和0.193;降解培养基溶液COD的去除率分别为59.4%、65.3%、69.2%和70.6%,说明BFN菌在生长的过程中利用萘作为碳源。同时,动力学拟合发现,对不同含量萘的降解过程都符合一级降解动力学方程,且BFN菌的生长过程满足逻辑斯蒂方程。扫描电镜图表明,BFN菌在萘的存在下生长得更好。紫外光谱显示波长为276 nm的萘的吸收峰在降解后下降很多。红外光谱数据则表明,降解液中有2组新的吸收峰出现:一组出现在2 878、2 930和2 968 cm-1处,说明在萘的降解过程中有新的羧酸类生成;另一组出现在3 438、3 667和3 731 cm-1处有新的酚类物质生成。     

Di-n-butyl phthalate degrading endophytic bacterium Bacillus amyloliquefaciens subsp. strain JR20 isolated from garlic chive and its colonization in a leafy vegetable

The bioconcentration and elimination of racemic benalaxyl (BX) in trout liver microsomes and in juvenile rainbow trout (Oncorhynchus mykiss) were investigated to determine whether the fish can bioconcentrate and degrade this fungicide enantioselectively. Both enantiomers of BX were extracted with organic solvents and evaluated using high-performance liquid chromatography. In the microsomes, BX degradation followed first-order kinetics, and the S?(+) enantiomer of BX was eliminated twice as rapidly as the R?(?) enantiomer, resulting in residues enriched for R?(?)?BX. In vivo experiment, chiral analysis showed an obvious selective bioconcentration of BX based on statistically altered enantiomer fractions (EFs) in the fish compared with the values in the water. The R?(?)?BX was initially preferentially bioconcentrated by rainbow trout and then dissipated more slowly than its antipode. The mean half-lives for individual enantiomers were calculated as 31.6 h for R?(?)?BX and 20.3 h for the S?(+)?form. The results of the study showed that the degradation of BX enantiomers was stereoselective in rainbow trout.     

Influence of surfactant concentration on foliar retention of pesticides used in forestry

Abstract

Aqueous tank mixes of permethrin, fenitrothion, Bacillus thuringiensis (B.t.), diflubenzuron (DFB), and glyphosate containing different amounts of Triton® X‐114, a nonionic surfactant, were prepared. Glyphosate formed clear solutions, permethrin and fenitrothion formed emulsions, DFB and B.t provided suspensions. Emulsion stability of permethrin and fenitrothion increased with increasing surfactant level, while the emulsion drop size decreased.

Foliage of white oak, trembling aspen, white spruce and balsam fir were dipped in tank mixes of pesticides (except B.t.) labelled with ¹⁴carbon. The amount of pesticide retained on foliage was determined by liquid scintillation counting. Foliage was also dipped in non‐radioactive B.t. tank mixes, and the protein retained was determined colorimetrically. With all tank mixes, a direct relationship was observed between the mass of liquids retained on foliage and liquid viscosity. In contrast, the amount of pesticide retained was unaffected by viscosity, but was influenced by emulsion drop size. Initially, the amount of pesticide retained on foliage increased with increasing surfactant concentration. Beyond an optimum surfactant level, the emulsion drop sizes were too small and the emulsions became too stable to allow maximum retention of pesticides on foliage. With the glyphosate solutions, however, no optimum surfactant level was indicated because foliar concentrations continued to increase with increasing surfactant levels.     

Effects of droplet density and concentration on the efficacy of bacillus thuringiensis and carbaryl against gypsy moth larvae (Lymantria dispar L.)

Abstract

The feeding behavior of gypsy moth larvae exposed to two pesticide deposits (Bt and carbaryl) on oak leaf disks was monitored to determine the relationships between its efficacy and application parameters (droplet density and pesticide concentration). A range of pesticide concentrations and droplet densities (from 9 to 149 droplets/cm²) was used to simulate high and low application rates produced by different methods of application in the field.

The LD₅₀ and the LC₅₀, appeared to be affected by the spatial distribution of the deposit on the leaf surface. Both Bt and carbaryl showed a decreasing LD₅₀ at increasing time after spray. The LD₅₀ of Bt decreased from 14.1 BIU/liter to 3.1 BIU/Iiter between 48 and 144 hours after spray. The results show that feeding inhibition by Bt is more closely related to concentration than to droplet density and dose per unit area with the highest feeding inhibition occurring at 10 BIU/liter at 9 droplets/cm². With carbaryl, an increase in both concentration and droplet density was necessary to cause a decrease in leaf area eaten by larvae.     

Influence of extracellular polymeric substances (EPS) on Cd adsorption by bacteria

The role of extracellular polymeric substances (EPS) in Cd adsorption by Bacillus subtilis and Pseudomonas putida was investigated using a combination of batch adsorption experiments, potentiometric titrations, Fourier transform infrared spectroscopy (FTIR). An increased adsorption capacity of Cd was observed for untreated bacteria relative to that for EPS-free bacteria. Surface complexation modeling of titration data showed the similar pK_a values of functional groups (carboxyl, phosphate and hydroxyl) between untreated and EPS-free bacteria. However, site concentrations on the untreated bacteria were found to be higher than those on the EPS-free bacteria. FTIR spectra also showed that no significant difference in peak positions was observed between untreated and EPS-free bacteria and carboxyl and phosphate groups were responsible for Cd adsorption on bacterial cells. The information obtained in this study is of fundamental significance for understanding the interaction mechanisms between heavy metals and biofilms in natural environments.     

Chromium phytoextraction and physiological responses of the hyperaccumulator Leersia hexandra Swartz to plant growth-promoting rhizobacterium inoculation

● Improved Cr phytoextration efficiency was achieved by B. cereus inoculation. ● B. cereus could produce plant-beneficial PGPR factors at diverse Cr stresses. ● Enhanced resistance of inoculated L. hexandra towards elevated Cr stress. ● The majority of Cr existed in the stable forms in the tissues of L. hexandra. Phytoextraction is a promising option for purifying hexavalent chromium (Cr(VI))-laden wastewater, but the long remediation period incurred by poor growth rate of Cr hyperaccumulators remains a primary hindrance to its large-scale application. In this study, we performed a hydroponic experiment to evaluate the feasibility of promoting the growth and phytoextraction efficiency of Cr hyperaccumulator Leersia hexandra Swartz (L. hexandra) by inoculating plant growth-promoting rhizobacteria (PGPR) Bacillus cereus (B. cereus). In batch tests, the Cr(VI) removal rates of L. hexandra and B. cereus co-culture were greater than the sum of their respective monocultures. This was likely due to the microbial reduction of Cr(VI) to Cr(III), which is amiable to plant uptake. Besides, the PGPR factors of B. cereus, including indoleacetic acid (IAA) production, 1-aminocyclopropane-1-carboxylic acid deamination (ACCd) activity, phosphate solubilization capacity, and siderophore production, were quantified. These PGPR factors helped explain the biomass augmentation, root elongation and enhanced Cr enrichment of the inoculated L. hexandra in pot experiments. Despite the increased Cr uptake, no aggravated oxidative damage to the cell membrane was observed in the inoculated L. hexandra. This was attributed to its capacity to confront the increased intracellular Cr stress by upregulating both the activities of antioxidative enzymes and expression of metal-binding proteins/peptides. Moreover, L. hexandra could always conserve the majority of Cr in the residual and oxalic integrated forms with low mobility and phytotoxicity, irrespective of the B. cereus inoculation. These results highlight the constructed Cr hyperaccumulator-rhizobacteria consortia as an effective candidate for decontaminating Cr(VI)-laden wastewater.     

纳米银复合材料与抗生素的联合抗菌性能及相关机制研究

抗生素的滥用导致细菌耐药问题日益严重,人类迫切需要开发出新的抗菌药物以减少细菌耐药问题。基于纳米银制备而成的纳米银复合材料在兼顾纳米银抗菌性能的同时不仅能够克服单一纳米银释放速度快、不稳定等缺点,还能缓解细菌耐药的问题,因此被认为是一类具有广泛应用前景的新型抗菌剂。已有研究表明,单一纳米银与某些抗生素的联合使用可以达到协同抗菌效果,但目前尚缺乏对纳米银复合材料与抗生素的联合抗菌性能及机制的研究。本文首先制备出3种不同结构的纳米银复合材料,包括二氧化硅-聚多巴胺-纳米银复合材料(SiO_2-PD-AgNPs)、纳米银@二氧化硅复合材料(AgNPs@SiO_2)和纳米银@二氧化硅-聚多巴胺-纳米银复合材料(AgNPs@SiO_2-PD-AgNPs)。随后测定了纳米银复合材料对大肠杆菌(Escherichia coli, E. coli)和枯草芽孢杆菌(Bacillus subtilis, B. subtilis)的单一毒性效应。结果显示,AgNPs@SiO_2-PD-AgNPs复合材料对2种菌的单一毒性均大于其余2种纳米银复合材料。因此,笔者以AgNPs@SiO_2-PD-AgNPs作为代表,测定了纳米银复合材料与硫酸卡那霉素(kanamycin sulfate, KS)/盐酸土霉素(oxytetracycline hydrochloride, OH)的二元联合抗菌性能,发现AgNPs@SiO_2-PD-AgNPs与KS联合可以对E. coli产生协同效应。协同效应产生的主要原因可能是:AgNPs@SiO_2-PD-AgNPs释放出的纳米银会和KS发生键合反应生成KS-纳米银复合物,导致纳米银释放出大量的Ag+增加了细胞膜的通透性,从而使得进入细菌内的Ag~+和KS比单独作用时进入胞内的抗菌剂增多,产生更强的抗菌性能,从而表现出协同抗菌效应。本研究基于新型纳米银复合材料与抗生素的联合抗菌性能实验探究了纳米银复合材料与特定抗生素联合用药的最佳组合和相关机制,为今后开发新型抗菌材料提供了新思路并为相关联合用药提供参考。     

土壤分离菌株去除水溶液中铅离子研究

金属及微生物种类、pH和接触时间是决定生物吸附效果的关键因素.从受铅污染的土壤中分离出5株有生物吸附铅离子能力的菌株,并鉴定吸附能力最强的菌株1为芽孢杆菌;试验了pH、接触时间和初始铅离子浓度对该芽孢杆菌生物吸附铅的影响,在温度为25℃时,pH值3.0、初始铅离子浓度250 mg/L、吸附时间不超过15 min有最大吸附量92.27 mg/g,此时去除率为73.82%,且25℃吸附平衡基本符合Langmuir等温模型.因此,用该芽孢杆菌生物吸附去除水溶液中铅是可行的.     

苏云金芽孢杆菌无质粒突变株BMB171的转化和表达性能

研究了苏云金芽孢杆菌无质粒突变株ＢＭＢ１７１的转化性能和表达ｃｒｙ１Ａｃ和ｃｒｙ１Ｃａ基因的性能．用ｐＨＴ３１０１、ｐＢＭＢ３０５、ｐＢＭＢ１７３６、ｐＢＭＢ６７１、ｐＢＴＬ１和ｐＨＶ１２４９等６种外源质粒电转化无质粒突变株ＢＭＢ１７１,其转化频率分别是Ｂｔ４Ｑ７、Ｂｔ４Ｄ１０和Ｂｔｉ．ＩＰＳ．７８／１１等３种常用受体菌相应最高转化频率的１０００、６．７、１２．５、６６．７、３５００和２倍,其每μｇＤＮＡ的最高转化子数达１０７．导入ＢＭＢ１７１的外源质粒的稳定性与其复制子类型和质粒大小有关．无质粒突变株ＢＭＢ１７１表达ｃｒｙ１Ａｃ基因的表达量高于对照受体菌Ｂｔ４Ｑ７,略低于Ｂｔ４Ｄ１０和Ｂｔｉ．ＩＰＳ．７８／１１,而ＢＭＢ１７１表达ｃｒｙ１Ｃａ基因的表达量高于这３种受体菌;对小菜蛾３龄幼虫和甜菜夜蛾初孵幼虫的毒力测定结果表明,ＢＭＢ１７１表达ｃｒｙ１Ａｃ基因的杀虫毒力高于Ｂｔ４Ｑ７和Ｂｔ４Ｄ１０,略低于Ｂｔｉ．ＩＰＳ．７８／１;而表达ｃｒｙ１Ｃａ基因的毒力高于这３种受体菌     

BACILLUS SP. BT-7木聚糖酶基因克隆与鉴定

报道了从一株有较高半纤维素酶活性的Ｂａｃｉｌｕｓｓｐ．ＢＴ７克隆内切木聚糖酶基因的结果．以大肠杆菌ＸＬ１ｂｌｕｅ为宿主菌,采用水解圈检测法,在含有ＲＢＢ木聚糖（４氧甲基Ｄ葡萄糖苷Ｄ木聚糖Ｒｅｍａｚｏｌ亮蓝Ｒ）的平板上分离到能水解ＲＢＢ木聚糖的阳性克隆３个,对它们进行的限制酶作图和Ｓｏｕｔｈｅｒｎ杂交分析表明,它们属于３种不同的内切木聚糖酶基因