Adsorption and desorption of monomeric Bt (Bacillus thuringiensis) Cry1Aa toxin on montmorillonite and kaolinite

Genetically modified crops, which produce pesticidal proteins from Bacillus thuringiensis, release the toxins into soils through root exudates and upon decomposition of crop residues. Although the phenomena of gene transfer and emergence of resistance have been well documented, the fate of these toxins in soil has not yet been clearly elucidated. The aim of this study was to elucidate the adsorption and the desorbability of the Cry1Aa Bt insecticidal protein in contact with two sodium-saturated clays: montmorillonite and kaolinite. Because the toxin is released into soil in small quantities, it was assumed that it will be in a monomeric state in solution until it oligomerized on cell membranes. The originality of this study was to focus on the monomeric form of the protein. Specific sample conditions were required to avoid polymerisation. A pH above 6.5 and an ionic strength of at least 150 mM (NaCl) were necessary to keep the protein in solution and in a monomeric state. The adsorption isotherms obtained were of the L-type (low affinity) for both clays and fitted the Langmuir equation. The adsorption maximum of the toxin, calculated by the Langmuir nonlinear regression, decreased with increasing pH from 6.5, which was close to the isoelectric point, to 9. At pH 6.5, the calculated adsorption was 1.7 g g⁻¹ on montmorillonite and 0.04 g g⁻¹ on kaolinite. Desorbability measurements showed that a small fraction of toxin could be desorbed by water (up to 14%) and more by alkaline pH buffers (36 ± 7%), indicating that it was not tightly bound. Numerous surfactants were evaluated and the toxin was found to be easily desorbed from both clays when using zwitterionic and nonionic surfactants such as CHAPS, Triton-X-100, and Tween 20. This finding has important implications for the optimization of detection methods for Bt toxin in soil.     

Clays as dietary supplements for swine: A review

Clays are crystalline, hydrated aluminosilicate molecules composed of alkali and alkaline earth cations along with small amounts of various other elements. The best-known are montmorillonite, smectite, illite, kaolinite, biotite and clinoptilolite. The molecules in these clays are arranged in three-dimensional structures creating internal voids and channels capable of trapping a wide variety of molecules. As a result of this structure, clay minerals are regarded as a simple and effective tool for the prevention of the negative effects of many toxic compounds. Dietary supplementation with clays has been shown to improve weight gain and feed conversion in pigs. Where improvements in performance have been noted, one of the most likely explanations for the improvement is the fact clays increase nutrient digestibility. Clays reduce the speed of passage of feed along the digestive tract which allows more time for digestion. Feeding clays also causes morphological changes in the intestinal mucosa such as an increase in villus height and an increase in the villus height to crypt depth ratio. These changes increase the surface area of the gastrointestinal tract thus increasing nutrient digestibility. Several studies have indicated that feeding clay reduces the incidence, severity and duration of diarrhea in pigs. The mechanism for the reduction in diarrhea is likely due to increases in the numbers of Bifidobacteria and Lactobacillus and decreases in Clostridia and E. coli in the small intestine of pigs fed clays. In addition, the numbers of pigs born alive and weaned, birth weight and weaning weight have been shown to be higher for sows fed clays. Several studies have indicated that clays can help mitigate the effects of mycotoxins. The aim of the present review is to focus on the various clays which have been given attention in recent research and to discuss their potential to improve pig performance.     

新型吸附剂AAN对黄曲霉毒素B1、B2、G1、G2的体外吸附研究

 对蒙脱石进行复合改性，构建了新型纳米吸附材料AAN，分别从振荡时间、吸附剂用量、溶液pH、平衡温度几个方面研究了AAN对黄曲霉毒素B1、B2、G1、G2的吸附情况，确定了最佳吸附条件。结果表明AAN对黄曲霉毒素的吸附作用强，二者之间的吸附属于强化学吸附；吸附速度快，60min可以达到吸附平衡；解吸率低，小于10％。这些结果提示AAN作为一种新型纳米吸附剂，应用前景十分广阔。     

还原态蒙脱石结构Fe（Ⅱ）催化水铁矿转化特性及影响因素

还原条件下土壤中Fe(Ⅱ)催化水铁矿转化在调控营养元素和污染物的生物地球化学过程中具有重要作用。然而,作为土壤中Fe(Ⅱ)存在的主要形态之一,蒙脱石结构中Fe(Ⅱ)催化水铁矿转化的特性及其影响因素目前尚不清楚。以化学还原的蒙脱石为研究对象,探究还原态蒙脱石(rSWy-2)结构中Fe(Ⅱ)催化水铁矿转化的特性及其影响因素。结果表明,贫铁的蒙脱石结构中Fe(Ⅱ)可催化水铁矿向纤铁矿转化,反应96 h后水铁矿转化量达到83.3%。X射线衍射(XRD)、高分辨透射(HRTEM)、球差电镜(STEM)和表面吸附态Fe(Ⅱ)含量分析表明,rSWy-2结构Fe(Ⅱ)催化水铁矿转化主要经历矿物间固相吸附、电子传递和水铁矿转化三个阶段,形成的纤铁矿呈板状纳米片,尺寸大小为100～200 nm。溶液中Na+和Cl–离子对rSWy-2催化水铁矿转化影响较弱,而Ca²⁺、SO₄^2-、有机质和As(Ⅲ)均对水铁矿转化具有明显的抑制作用。     

土壤调理剂对金乡杂交蒜生长发育和产量的影响

研究了蒙脱石和麦饭石两种不同类型的土壤调理剂对大蒜生长发育和产量的影响。结果表明：施用蒙脱石和麦饭石均可增加大蒜的株高、茎粗、叶片数和叶面积,降低大蒜叶枯病的发生,提高蒜头和蒜薹产量;蒙脱石比对照增产蒜头11．0％,增产蒜薹19．0％;而麦饭石比对照增产蒜头8．5％,增产蒜薹4．9％。两种调理剂相比较,蒙脱石效果好于麦饭石。     

副溶血弧菌噬菌体的吸附材料选择及其吸附和洗脱作用

[目的]选择副溶血弧菌噬菌体的适宜吸附剂,并研究其吸附和洗脱作用。[方法]比较了滑石粉+硅藻土(3∶1)、活性炭、蒙脱石、玻璃纤维4种吸附剂对副溶血弧菌噬菌体的吸附固定化效果以及洗脱效果。[结果]蒙脱石和玻璃纤维对噬菌体的吸附效果好。通过单因素试验和正交试验研究蒙脱石用量、吸附时间、吸附液p H对噬菌体固定化的影响,结果发现当蒙脱石用量为0.5 g,吸附时间为1 h,吸附液p H为6.0时,吸附效果最佳。[结论]将副溶血弧菌噬菌体制成固定化制剂后分别作用于养殖动物和养殖水体,可以达到对养殖动物进行生物防治和改善水体环境的目的。     

PAA-AM/SH/MMT多功能保水剂的溶胀和保水性能研究

以丙烯酸(AA)、丙烯酰胺(AM)、腐殖酸钠(SH)和膨润土(MMT)为原料,采用水溶液聚合法合成了聚(丙烯酸-丙烯酰胺)/腐殖酸钠/膨润土复合多功能保水剂(PAA-AM/SH/MMT)。开展了复合多功能保水剂吸水速率、不同pH溶液和重复使用的溶胀行为以及在实际土壤中保水效果的研究。结果表明:与单独引进SH或MMT相比,在PAA-AM体系中同时引入SH和MMT所制备的多功能保水剂,不仅具有较快的吸水速率,而且具有良好的反复使用性能和较好的保水性能。     

Physiopathological effects of zearalenone in post-weaning female piglets with or without montmorillonite clay adsorbent

Zearalenone (ZEA), commonly present in corn and its derived products for animals, has caused significant economical impact on swine reproduction in China. The present study therefore attempted to reveal the adverse effects of ZEA (1.3 mg/kg diet) exposure from a viewpoint of damages focusing on the liver and kidney of female piglets. The efficacy of dietary montmorillonite clay in preventing ZEA-induced adverse effects was also determined. Treatments were 1) control; 2) control + 2.5 g/kg clay; 3) control + 1 mg/kg ZEA; 4) control + 1 mg/kg ZEA + 1.25 g/kg clay; 5) control + 1 mg/kg ZEA + 2.5 g/kg clay; 6) control + 1 mg/kg ZEA + 5.0 g/kg clay; 7) control + 1 mg/kg ZEA + 10 g/kg clay. Results showed that pigs fed ZEA-contaminated diet reduced (P < 0.05) platelets, haemoglobin, globulin, triglycerides and high density lipoproteins (HDL) in serum, and increased (P < 0.05) all enzymes activities, cholesterol, urea, and creatinine. Degeneration of the liver and kidney tissues was also found in female piglets fed 1.3 mg/kg ZEA-contaminated diet. Dietary addition of clay showed a positive protection effect on ZEA feeding, and the linear or quadratic effect (P < 0.05) on neutralizing detrimental effects of clay in ZEA feeding were observed. It suggested that feeding ZEA at 1.3 mg/kg diet for 24-d may result in a deleterious effect in female piglets, and clay addition at 5 or 10 g/kg diet can effectively protect against the detrimental effects of the ZEA feeding. These results may have implications for human and animals consuming ZEA-contaminated food or feed.     

蒙脱石改性前后对3种常见霉菌毒素的吸附效果及结构表征

本试验旨在研究蒙脱石经不同改性处理后对3种常见霉菌毒素的脱毒能力,以获得最佳的改性处理方法,并对蒙脱石改性前后结构进行表征。利用季铵盐及载金属离子对蒙脱石进行改性处理,测定改性前后对黄曲霉毒素B1(AFB1)、玉米赤霉烯酮(ZEN)和脱氧雪腐镰刀菌烯醇(DON)的吸附效果,并对蒙脱石原料及最佳改性处理后材料进行结构表征。结果表明:蒙脱石经6种改性处理后对3种霉菌毒素的吸附能力均显著增强(P<0.05),其中十八烷基三甲基氯化铵(STAC)改性处理后对AFB1、ZEN和DON吸附能力达到最大,分别为99.48%、93.62%和67.38%;结构表征结果显示,改性后蒙脱石的孔径、孔体积及比表面积均显著增加(P<0.05),红外光谱中出现STAC的特征峰,并检测到C、H和N元素。综上,利用载金属离子和季铵盐改性均能显著提高蒙脱石的脱毒能力,其中STAC改性是最佳改性方式;改性处理后蒙脱石分子结构疏松,STAC基团成功插层到蒙脱石分子结构中,更有利于加强对霉菌毒素的吸附能力。     

蒙脱石纳米复合物的制备及其吸附作用研究

对天然蒙脱石(M)矿物进行钠化改型和柱撑复合，制备了蒙脱石纳米复合物(MN)，并对其进行表征，同时研究其对黄曲霉毒素的吸附作用。结果表明：与M相比，MN的层间距和比表面积明显增大，d₍₀₀₁₎值增加到1.96 nm，比表面积达到149.68m²/g，而且孔体积增加，孔直径缩小，微孔比例提高。吸附试验表明：复合改性后，MN对黄曲霉毒素的吸附容量和吸附速率均明显优于M。这些结果提示MN可望成为性能优越的黄曲霉毒素吸附剂。