Biosynthesis of nanocrystalline silver chloride with high antibacterial activity using bacterial extracts

The traditional synthesis of nano silver chloride involves chemical precipitation or physical methods.Due to the hazardous substances generated during the synthesis,it can cause environmental pollution.In this study,a green and facile method is described to biosynthesize nano-silver chloride with excellent antibacterial activity via in situ reduction of Ag t using the extract of Bacillus thuringiensis(Bt).Compared with previous reports,the minimal inhibition concentration(MIC)against Escherichia coli(E.coli)is 3.0μg/mL,which is 2–to 800-fold higher than that of nano silver chloride.Subsequent in vitro studies involving agricultural bacteria such as Ralstonia solanacearum(R.solanacearum)revealed a 92.95%antibacterial rate when the concentration of nano-silver chloride was 2.0μg/mL.Previous studies of antibacterial activity of nano-silver chloride focused more on the basic antibacterial properties without describing its antibacterial molecular mechanisms.The microscopic investigations and DNA damage experiments indicated that the nano-silver chloride adsorbed to the bacterial surface,leading to cell wall rupture,DNA damage,and cytoplasmic leakage.In addition,electron paramagnetic resonance(EPR)spectroscopy indicated the synthesis of reactive oxygen species(⋅OH,⋅O^(2-) and ^(1)O_(2))in the bacteria.Our study provides evidence supporting the use of nano-silver chloride as an antibacterial agent in agriculture,and theoretical insight into the antibacterial mechanism thereof.

Layer-by-Layer Assembled Bacterial Cellulose/Graphene Oxide Hydrogels with Extremely Enhanced Mechanical Properties

Uniform dispersion of two-dimensional(2 D) graphene materials in polymer matrices remains challenging. In this work, a novel layer-by-layer assembly strategy was developed to prepare a sophisticated nanostructure with highly dispersed 2 D graphene oxide in a three-dimensional matrix consisting of onedimensional bacterial cellulose(BC) nanofibers. This method is a breakthrough, with respect to the conventional static culture method for BC that involves multiple in situ layer-by-layer assembly steps at the interface between previously grown BC and the culture medium. In the as-prepared BC/GO nanocomposites, the GO nanosheets are mechanically bundled and chemically bonded with BC nanofibers via hydrogen bonding,forming an intriguing nanostructure. The sophisticated nanostructure of the BC/GO leads to greatly enhanced mechanical properties compared to those of bare BC. This strategy is versatile, facile, scalable, and can be promising for the development of high-performance BC-based nanocomposite hydrogels.

In situ biosynthesis of bacterial cellulose hydrogel spheroids with tunable dimensions

Bacterial cellulose(BC)hydrogel spheroid plays a significant role in diverse fields due to its spatial 3D structure and properties.In the present work,a series of BC spheroids with controllable size and shape was obtained via an in situ biosynthesis.Crucial factors for fabricating BC spheroid in-cluding inoculum concentration of 1.35×10^(3)CFU/mL,shaking speeds at 100 r/min,and 48-96 h incubation time during the biosynthetic process,were comprehensively established.An operable mechanism model for tuning the size of BC spheroids from 0.4 to 5.0 mm was proposed with a fresh feeding medium strategy of dynamic culture.The resulting BC spheroids exhibit an inter-active 3D network of nanofibers,a crystallinity index of 72.3%,a specific surface area of 91.2 m^(2)/g,and good cytocompatibility.This study reinforces the understanding of BC spheroid forma-tion and explores new horizons for the design of BC spheroids-derived functional matrix materials for medical care.

Role of bacteria in carcinogenesis, with special reference to carcinoma of the gallbladder

Carcinoma of the gallbladder (CaGB) is the fifth commonest gastrointestinal tract cancer and is endemic in several countries. The interplay of genetic susceptibility, infections, and life style factors has been proposed to be responsible for carcinogenesis of gallbladder. Persistence of infection leading to chronic inflammation, and production of certain toxins and metabolites with carcinogenic potentials, by certain bacteria has been speculated to be involved in the transformation of the gallbladder epithelium. Therefore, any bacteria that have evolved to acquire both of the above carcinogenic mechanisms can cause cancer. Salmonella typhi has been found to be prominently associated with CaGB. Chronic typhoid carriage (persistence) and production of mediators of chronic infl ammation and a genotoxic toxin (cytotoxic distending toxin, CdtB) are also known for this bacterium. Furthermore, the natural concentrating function of the gallbladder might amplify the carcinogenic effect of the mediators of carcinogenesis. In addition to S. typhi, certain species of Helicobacter (H. bilis and H. hepaticus) and Escherichia coli have also been implicated in carcinogenesis. As the isolation rate is verypoor with the presently available culture techniques, the existence of bacteria in a viable but non-cultivable state is quite likely; therefore, sensitive and specif ic molecular techniques might reveal the etiological role of bacterial infection in gallbladder carcinogenesis. If bacteria are found to be causing cancers, then eradication of such infections might help in reducing the incidence of some cancers.

Generation of Reactive Oxygen Species in Different Fractions of the Coelomocytes of Holothurian Eupentacta fraudatrix in Response to the Thermostable Toxin of Yersinia pseudotuberculosis in Vitro

Pure fraction (92%-95%) of phagocytes (FP) and a mixture of amoebocytes(62%) and morula cells (38 %) FPMC of the holothurian Eupentacta fraudatrix (Holothuroidea, Dendrochirota) were obtained by using ficoll verographine step gradient. Basal production of reactive oxygen species (ROS) in FP quantified by using reduction of nitroblue tetrazolium (NBT) was more than twice that in FPMC. Thermostable toxin of Yersinia pseudotuberculosis (TST) at different concentrations ( 0.2; 0.5; 2.5 μg/ml, but not 0.1 μg/ml) stimulated NBT reduction in FPMC after 24 h incubation. In FP, TST at concentrations of 0.1 and 0.2 μg/ml inhibited and at concentrations of 0.5 and 2.5 μg/ml stimulated NBT reduction after 24 h incubation. Maximal effect was observed in FP and FPMC at TST concentrations of 0.5 and 0.2 μg/ml, respectively. Addition of catalase (0.7 μg/ml) to the cells treated with TST (2.5 μg/ml) was followed by a decrease in NBT reduction compared to that under toxin treatment alone. TST stimulated superoxide dismutase activity in concentration dependent manner (maximum at 0.5 μg/ml concentration in FP) after 24 h treatment, and this stimulation was prevented by a commercial catalase. Plant lectin concanavalin A stimulated NBT reduction more than 5 fold in FPMC compared to the control. With addition of TST, lectin stimulated ROS to lesser extent than that with lectin alone. When catalase, TST, and lectin were added into the FPMC simultaneously, ROS increase was similar to that under lectin treatment alone. On the whole, data obtained indicated that ROS generation in holothurian coelomocytes especially occurs in both stimulated and not stimulated phagocytes, and that changes in ROS production by these cells may be one of the mechanisms of antibacterial protection of holothurians.

Novel Experimental Strategy for High Resolution AFM Imaging of Membrane-Associated Bacterial Toxins

Bacterial pore-forming toxins(PFTs) are essential virulence factors of many human pathogens. Knowledge of their structure within the membrane is critical for an understanding of their function in pathogenesis and for the development of useful therapy. Atomic force microscopy(AFM) has often been employed to structurally interrogate many membrane proteins, including PFTs, owing to its ability to produce sub-nanometer resolution images of samples under aqueous solution. However, an absolute prerequisite for AFM studies is that the samples are single-layered and closely-packed, which is frequently challenging with PFTs. Here, using the prototypical member of the cholesterol-dependent cytolysin family of PFTs, perfringolysin O(PFO), as a test sample, we have developed a simple, highly robust method that routinely produces clean, closely-packed samples across the entire specimen surface. In this approach, we first use a small Teflon well to prepare the supported lipid bilayer, remove the sample from the well, and then directly apply the proteins to the bilayer. For reasons that are not clear,bilayer preparation in the Teflon well is essential. We anticipate that this simple method will prove widely useful for the preparation of similar samples, and thereby enable AFM imaging of the greatest range of bacterial PFTs to the highest possible resolution.

适配体生物传感器检测细菌毒素的研究进展

细菌毒素是细菌产生的次生代谢产物,是人类健康的主要威胁之一。食品中细菌毒素的污染已成为人们迫切关注的主要食品安全问题之一。因此,开发出简便、快速、灵敏检测食品中细菌毒素的方法具有重要意义。核酸适体是体外筛选的单链寡核苷酸序列,能特异性识别靶标。具有易合成、易标记、易修饰、高灵敏度、高特异性和低分子量等优点,被广泛用于生物传感器中。本文简要介绍了细菌毒素的分类及危害,重点综述了基于光学和电化学技术的适配体生物传感器在细菌毒素检测和定量方面的最新进展及应用,以期为细菌毒素的检测提供研究基础。

金属有机框架作为光化学传感器在食品分析中的应用

金属有机框架(MOFs)作为一种高稳定性、高灵敏度和快速响应的化学传感器,受到广泛关注。以MOFs作为光化学传感器在食品分析中的应用为例,总结了近年来MOFs在天然毒素、细菌污染物、农药残留三方面检测的重要研究工作,并对MOFs在该领域的发展前景进行了展望。

新型生物材料——细菌纤维素

简要介绍细菌纤维素的基本性质 ,系统地介绍了细菌纤维素的生物合成与调节、发酵工艺条件控制和在造纸、食品。

细菌纤维素改性研究进展

作为一种新兴的生物材料,细菌纤维素(BC)具有广阔的应用前景,通过对其改性制备多功能材料以拓展其应用领域是目前的研究热点之一。介绍了近年来BC生物改性和化学改性方面研究的进展,即在合成过程中添加物质对产物进行结构性能调控,以及得到BC后对其进行化学处理。进一步展望了该领域的发展潜力和前景。

赤潮藻毒素生物合成研究进展

合成毒素是赤潮藻类的一个常见特征,已知能够产生毒素的微藻有70多种。作为次级代谢产物,藻毒素的产生可能是一种压制或清除其它藻类竞争者的一种反应,在群落演替、种间竞争中发挥重要作用。目前,人们对藻毒素生物合成机理依然知之甚少,相关基因的研究仍无明显突破。利用环境因子诱导毒素生成变化进而分离差异表达基因或者比较不同产毒藻株间基因表达的差异,从中克隆藻毒素生物合成基因似乎是一种极具潜力的研究方向。

细菌纤维素的生物合成及在食品工业的应用

细菌纤维素是经微生物发酵形成的新型生物合成材料,具有机械强度高、吸水性能好、纯度高、结晶度高等优良特性,广泛应用于食品工业等领域。已报道的产细菌纤维素的细菌有醋酸菌属(Acetobacter)、根瘤菌属(Rhizobium)、八叠球菌属(Sarcina)、土壤杆菌属(Agrobaeterium)、假单胞菌属(Preudomonas)、无色杆菌属(Achromobacter)、固氮菌属(Azotobacter)、气杆菌属(Aerobacter)和产碱菌属(Alcaligenes)这9个属中的某些种,真正能够应用于工业化生产细菌纤维素的只有醋酸菌中的几个种,他们是木醋杆菌(Acetobacter xylinum)、醋化醋杆菌(Acetobacteraceti)、产醋醋杆菌(Acetobacteracotigenum)和巴氏醋杆菌(Acetobacter pastcurianum)。本文通过分析近期国内外与细菌纤维素相关文献,对其高产菌种选育、培养基优化和发酵模式等方面的研究进行综述,并展望其在食品工业中的应用前景,为进一步深入研究细菌纤维素提供理论基础和科学依据。

细菌胞外多糖的生物合成与基因控制

细菌胞外多糖是指细菌在生长发育过程中合成并分泌到细胞外的长链,高分子糖类聚合物。细菌胞外多糖的生物合成途径涉及装配、多聚化及运输三个过程,是多种酶和转运系统的结果,其发生的部位包括胞内和胞外,有些合成过程会发生在细胞壁上,对于胞外多糖合成相关基因的报道,发现控制胞外多糖合成是一大类基因簇,不同的菌株其基因簇的数量和种类各不相同。这些研究的不断更新为将来胞外多糖的应用提供了更加广阔的前景。

2006--2011年60株血感染金黄色葡萄球菌毒素及耐药基因分析

目的了解2006—2011年临床分离的60株血感染金黄色葡萄球菌的耐药情况及毒素基因和耐药基因的流行情况。方法 VITEK2-compact全自动细菌鉴定仪及配套鉴定卡、药敏卡对细菌进行鉴定及药敏试验;头孢西丁纸片扩散法筛选耐甲氧西林金黄色葡萄球菌(MRSA);应用聚合酶链反应(PCR)检测mecA、耐消毒剂基因(qacA)、杀白细胞素基因(pvl)、肠毒素基因(sea、seb、sec1、sed、see)及中毒休克综合征毒素-1基因(tst)。结果 60株金黄色葡萄球菌对青霉素的耐药率最高(91.7%),其次为红霉素(65.0%)、克林霉素(65.0%)、庆大霉素(40.0%)。未发现万古霉素、利奈唑胺、替加环素耐药菌株。其中携带耐药基因mecA13株(21.7%)、qacA3株(5.0%)、检出毒素基因pvl4株(6.7%)、肠毒素基因sea20株(33.3%)、seb3株(5.0%)、sec9株(15.0%)及sed7株(11.7%),未检出see及tst。结论血感染的金黄色葡萄球菌对青霉素、红霉素、克林霉素、庆大霉素耐药率高,同时携带多种毒素及耐药基因,临床应加强毒素及耐药基因检测。

ELISA技术在水产养殖病害诊断和海洋生物毒素检测中的应用进展

对ELISA技术原理及在水产养殖细菌性病害、病毒性病害及海洋生物毒素检测中的应用情况作一综述。ELSIA技术基础是抗原抗体特异性反应,样品与酶标记物和抗体在板孔中反应,洗去未结合的酶标记物,加入发色剂进行孵育,结合的酶标记物使发色剂颜色发生变化,最后加入终止液,在合适的波长下测定吸光度值。水产养殖中常见的细菌性病原为弧菌和嗜水气单胞菌,利用已建立的ELISA技术对大黄鱼肝脏中副溶血性弧菌含量进行测定,检出率为70%。嗜水气单胞菌的单克隆抗体技术分析也取得了较大进展,对于分泌抗嗜水气单胞菌单克隆抗体的细胞株,ELSIA分析可为快速、准确诊断鱼类嗜水气单胞菌提供可靠方法。20世纪90年代末,已有学者利用ELISA技术测定了草鱼出血病病毒(GCHV)的毒力,30 min内即可从未经提纯的毒液中检测出抗原,比较Dot-ELISA和SPA-CoA测定效果,发现灵敏度比SPA-CoA提高了10倍。对于虾类病毒性病原,ELISA测定主要涉及杆状病毒和白斑综合症病毒,其中对中国对虾杆状病毒检测灵敏度可达到60 ng,对同一个池白斑综合症发病率检测,检出率可达61.8%。利用ELSIA技术测定海洋生物毒素要求快速、方便、准确,日本于20世纪90年代初率先研制出检测DSP主要毒素软海绵酸(OA)的ELISA方法,美国和德国使用抗石房蛤毒素(saxtoxins,STX)和抗neo-STX多克隆抗体建立ELISA法测定PSP,可同时检测STX和neo-STX,灵敏度为40μg/(100 g)。虽然利用ELISA技术测定海洋生物毒素已经取得了一定进展,但是在检测过程中容易发生抗体交叉反应、系列标准毒素缺乏等因素仍然限制该方法的深入应用。

细菌纤维素的生物合成与发酵研究进展

细菌纤维素是一种由微生物合成的新型纳米材料,具有化学纯度高、持水性好、杨氏模量高、良好的生物相容性和可降解性等特性,广泛应用于食品、医疗、化工等领域。但发酵工艺落后、产量低、生产成本高一直是限制其应用于高附加值产品生产的瓶颈。本文概述纤维素产生菌及分离改良、发酵培养基优化、发酵条件对纤维素合成和产量的影响,以及发酵方式对BC产量和性能影响等方面的研究进展,并对BC在生产中的不足和未来应用前景进行展望,为开展更深入的研究和实际生产提供一定借鉴。

利用椰子水生物合成CMC改性细菌纤维素

以椰子水为培养基,于培养基中添加羧甲基纤维素(CMC)后培养木醋杆菌可制备羧甲基纤维素改性细菌纤维素(CMC-BC)。当添加6g/LCMC时,CMC-BC产量达到最大(10.41g/L),是纯BC产量(4.73g/L)的2.2倍。采用FTIR表征了产物结构;通过SEM、XRD、TGA研究了产物性能;并测试了产物的特性黏度与含水率。结果显示,利用椰子水所制备的CMC-BC缩短了培养时间(3d)。适量添加CMC〔ρ(CMC)=2～18g/L〕时,CMC-BC的聚合度增大,且具有较好热稳定性及较高含水率。CMC-BC还表现出较好的溶解性能。

人CEA启动子调控ADP核糖化毒素基因治疗大肠癌

目的 应用ADP核糖化细菌毒素基因探讨对CEA阳性大肠癌的组织特异性基因疗法。方法 从铜绿假单孢菌基因组DNA和质粒 pET15b DT中分别克隆假单孢菌外毒素Ⅱ +Ⅲ区基因 (PEA)和白喉外毒素A链 (DTA)基因 ,引入Kozak序列 ,终止信号和酶切位点 ,测序后置于CEA启动子调控下克隆到逆转录病毒载体中。研究体外表达和裸鼠体内抗肿瘤能力。结果 体外荧光素酶共转染试验证明CEA启动子调控的毒性基因在CEA阳性大肠癌细胞中可以特异抑制报告基因表达。在裸鼠模型中 ,构建物与脂质体共转染肿瘤瘤体内可以使人大肠癌选择性消退 ,而对CEA阴性的肾癌模型无显著作用。

细菌纤维素——一种新兴的生物材料

文章就细菌纤维素的特点,生物合成途径,代谢调控,发酵方法,功能及应用等进行了详细阐述。

PVA对生物合成细菌纤维素膜拉伸性能的影响

BC膜生物合成的过程受培养基中加入不同浓度PVA的影响,会产生拉伸性能各异的BC膜。培养基中添加低浓度(20和40 g·L·1)聚乙烯醇(PVA)后BC膜产量和拉伸强度等指标均有提高,培养至96 h时20和40 g·L·1 PVA浓度的培养基中BC产量分别比对照组高出40.48%和16.9%,此时40 g·L·1 PVA培养基中BC膜的弹性模量和拉伸强度最大,分别为4.56 GPa和66.8 MPa;而添加高浓度(60和80 g·L·1)PVA后BC膜产量和拉伸强度均降低。X-射线衍射结果显示培养基中低浓度的PVA可以提高膜的结晶度,而高浓度的PVA降低BC膜的结晶度;扫描电镜照片显示培养基中添加低浓度PVA后形成的BC膜结构更为致密均匀。