氯灭活水中枯草芽孢杆菌的效果

以枯草芽孢杆菌(ATCC6633)作为难灭活微生物的代表,研究了氯对水体中芽孢的灭活效果,考察了氯浓度、作用时间、反应体系pH值、温度以及芽孢初始浓度等因素的影响。结果表明,氯对芽孢的灭活过程可分为延滞期和灭活期;初始氯浓度在2.06~10.30 mg·L^-1,反应时间0~166 min,pH值6~9,温度1~30℃,初始芽孢浓度10²~10¹² cfu·ml^-1范围内,消毒剂浓度和反应时间共同影响着氯对芽孢的灭活效果,提高消毒剂投量或延长消毒反应时间,均可提高灭活率;酸性条件下氯灭活芽孢的能力强于碱性条件下;随着温度的上升,氯对芽孢的灭活能力增强;芽孢的初始浓度对氯灭活芽孢的效能影响不大。初始氯投量为8.30 mg·L^-1,pH=7,芽孢初始浓度10⁶ cfu·ml^-1,温度分别为5℃和25℃下,枯草芽孢杆菌对氯消毒剂的抗性强于炭疽芽孢杆菌。     

Aluminum-based materials for inactivation of aerosolized spores of Bacillus anthracis surrogates

Energetic materials generating biocidal combustion products to disable airborne pathogenic microorganisms (including bio-threat agents) were designed as compounds of halogens and metals with high heats of oxidation. Thermally stable Al-based powders containing iodine and chlorine were prepared using ball-milling at room and cryogenic temperatures. Such powders can replace pure aluminum in metallized energetic formulations. Their stability and halogen release were quantified using thermo-gravimetric analysis. Ignition temperatures were determined by coating prepared powders onto an electrically heated filament. All prepared composites had lower ignition temperatures and longer combustion times compared to pure Al. In separate experiments, combustion products generated by injecting the prepared powders into an air-acetylene flame were mixed with a well-characterized bioaerosol. Inactivation of viable bioaerosol particles exposed to the heated combustion products for a short period of time (estimated to be 0.33 s) was quantified. The combustion products of materials investigated in this study effectively inactivated the aerosolized spores of two tested surrogates of Bacillus anthracis (B. atrophaeus and B. thuringiensis var kurstaki). A ternary composite with 20 wt% of iodine, 40 wt% of aluminum and 40 wt% of boron was found to be most attractive based on both its stability and efficiency in inactivating the aerosolized spores. The inactivation achieved was primarily attributed to chemical stresses as the thermal effect could not solely produce the high measured levels of inactivation. The findings point to a possible synergy of the thermal and chemical spore inactivation mechanisms.

© 2017 American Association for Aerosol Research     

Thermal instability in plane couette flow heated from below

The conditions marking the onset of natural convection due to buoyant forces are investigated in the thermal entrance region of horizontal plane Couette flow. The base temperature profile produced by pure forced convection is approximated as a fourth order polynomial using the integral method. With this approximate base-temperature profile stability criteria are obtained by means of the local stability analysis, its modification, and the natural-amplification analysis. The last one takes into consideration the axial amplification rate of disturbances at the onset of thermal instability. This new concept is tested here for the first time. The consideration of axial amplification of disturbances makes the system more stable. It is shown that the results of the natural-amplification analysis agree well with the existing experimental data.     

Collection of airborne spores by circular single-stage impactors with small jet-to-plate distance

Most of the commonly used bioaerosol samplers are single-stage impactors that meet the conventional Marple's design criteria: their non-dimensional jet-to-plate distance, $S/W$, is greater than the established threshold (1.5 for rectangular nozzles and 1 for the circular ones). Recent studies have shown that these samplers underestimate the concentration of airborne fungal spores because their cut-off size is about $2.5\mathrm{\mu }$m (Air-O-Cell and Burkard samplers) or greater while some fungal species produce spores of ca. 1.8–$2.5\mathrm{\mu }$m in aerodynamic diameter. In this study, we evaluated the single-stage circular-jet impactors with very small jet-to-plate distances ($S/W⪡1$). The laboratory and field data obtained with test particles of different sizes and different origin (biological and non-biological) demonstrated the feasibility of these “incorrectly designed” impactors for the spore collection and total enumeration (viable + non-viable spores). A decrease in the jet-to-plate distance resulted in a critical decrease of the impactor's cut-off size ($d_{50}$): from $2.5\mathrm{\mu }$m to about $1\mathrm{\mu }$m. This reduction of cut-off size makes such an impactor efficient for collecting spores of all fungal species ($⩾1.8\mathrm{\mu }$m) and even some bacterial species ($⩾1\mathrm{\mu }$m). Since the spore surface density across the circular deposit area was non-uniform, three sample reading procedures were evaluated: the entire area count, random partial count, and a partial count on a rectangular “diametric slice”. The collection efficiency data suggested that a relatively small jet-to-plate distance is likely to result in excessive shear forces in the impaction zone, thus enhancing the spore deaggregation and bounce. The coefficient of inter-sample variation of the field samples, collected by commercially available impactors with $S/W\approx 0.099$, did not exceed 50% for the total spore count. The highest variability was observed for Arthrospores, which were more aggregated than other types of fungi.     

Experimental investigation of the autoignition process during fuel injection into a heated air flow

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 1, pp. 9–12, January–February, 1989.     

Inactivation of aerosolized surrogates of Bacillus anthracis spores by combustion products of aluminum- and magnesium-based reactive materials: Effect of exposure time

Targeting bioweapon facilities may release biothreat agents into the atmosphere. Bacterial spores such as Bacillus anthracis (Ba) escaping from direct exposure to the fireball potentially represent a high health risk. To mitigate it, reactive materials with biocidal properties are being developed. Aluminum-based iodine-containing compositions (e.g., Al·I₂ and Al·B·I₂) have been shown to inactivate aerosolized simulants of Ba effectively, i.e., by factors exceeding 10⁴ when the spores are exposed to their combustion products over a short time (～0.33 s). This follow-up study aimed at establishing an association between the spore inactivation caused by exposure to combustion products of different materials and the exposure time. Powders of Al, Al·I₂, Al·B·I₂, Mg, Mg·S, and Mg·B·I₂ were combusted, and viable aerosolized endospores of B. thuringiensis var kurstaki (a well-established Ba simulant) were exposed to the released products for relatively short time periods: from ～0.1 to ～2 s. The tests were performed at two temperatures in the exposure chamber: ～170°C and ～260°C; both temperatures are lower than required for quick thermal inactivation of the spores. The higher temperature and exposure times above 0.33 s generated distinctively higher inactivation levels (as high as ～10⁵) for iodine-containing materials. We also observed inactivation levels of up to ～10³ at very short exposure times, 0.12s, in the presence of condensing MgO. However, the effect of MgO at longer exposure times became negligible. The biocidal effect of sulfur oxides was found to be weak. The study findings are crucial for establishing strategies and developing reaction models that target specific bioagent inactivation levels.

Copyright © 2018 American Association for Aerosol Research     

枯草芽孢杆菌E79分批发酵动力学

基于Logistic和Leudeking-Piret方程,根据分批发酵过程中菌体生长、产物积累、总糖消耗、还原糖消耗及反应体系pH值的变化规律构建枯草芽孢杆菌E79发酵过程中菌体细胞生长、产物合成及基质消耗的动力学模型,应用SPSS11.5软件对数据进行计算与分析,Oirgin 7.5软件经非线性拟合与优化,获得了最佳...     

轴流桨搅拌槽内轴向流动速度的研究

为研究轴流桨搅拌槽内轴向速度的分布,在直径为300 mm的平底圆筒搅拌槽内,采用相位多普勒粒子分析仪(PDPA)对轴流式搅拌器主流区的流场进行测量。在不同转速和离底间隙条件下,对挡板前轴向时均速度在径向和轴向的分布进行分析和研究,采用壁面射流理论,建立搅拌槽内壁面射流流动模型,揭示轴向流动特性。结果表明:轴向速度沿径向的分布具有相似性;轴向最大速度沿轴向衰减;轴向流边界沿轴向线性扩展。研究结果有助于进一步了解搅拌槽内部流动特性,为固-液悬浮操作、过程放大和搅拌设备的优化设计提供理论依据。     

An analysis of heat transfer during flow of an air/water mist across a heated cylinder

Equations are developed for predicting local heat-transfer coefficients over the forward-facing half of a cylinder during transverse, mist flow. At low approach velocities predicted values are found to be in good agreement with corresponding measured values. With increase in approach velocity, agreement is found to fall off owing largely to the onset of a severe splashing or bouncing action. This effect is examined, together with effects of evaporation and convection at the free surface of the liquid layer formed on the cylinder.     

Medium optimization and in vitro antioxidant activity of exopolysaccharide produced by Bacillus subtilis

The present study involves medium formulation using an agro waste, cane molasses, as the carbon substrate that was used instead of sucrose, to produce exopolysaccharide from Bacillus subtilis. Plackett Burman design was applied to evaluate twenty selected components, from which cane molasses, yeast extract, CaCl₂, NaCl were found to be significant for fermentation. To study the concentration of each component, response surface methodology experimental design was performed using central composite design. The response plots resulted in optimized conditions—Cane molasses-2.36%, Yeast extract-0.56%, NaCl–0.71%, CaCl₂ — 0.05%—which yielded 4.92 g/L at 48 h, at a temperature of 37 °C, initial pH 7 under still conditions. Antioxidant activity of EPS on DPPH resulted in a reducing capacity of 61.19%, at a concentration of 0.8mg/ml, greater than standard, Vitamin C. The biopolymer could thus be an ecofriendly product which can be subjected to various industrial and pharmaceutical applications.     

Thermal shock of alumina by compressed air cooling

Alumina samples has been submitted to mild thermal shocks by quenching in a compressed air flow and the critical temperature difference has been determined for increasing thermal shock severities. Then these critical shocks have been numerically simulated by varying the superficial heat exchange coefficient value until the maximal tensile stress reaches the material strength. The combination of experimental and numerical approaches leads to indirect estimate of the heat exchange coefficient values during the tests.     

Mechanism of formation of a heated ground layer by an intense air burst

A mathematical modeling study demonstrated the fundamental possibility of the formation of a heated layer (a meter-long layer of erosion vapor and air with temperatures of a few thousand degrees and a density 20–50 times lower than the normal air density) at the ground surface under the action of the long-distance traveling fireball radiation from an intense explosion at a moderate radiant flux density of about 1 GW/m² for a time of about 10 msec. The results of the numerical study agree with data from observations of the heated layer effect in nuclear-weapon tests. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 100–106, July–August, 2006.     

绿色荧光蛋白基因在枯草芽孢杆菌中的表达

目的探讨异源基因在枯草芽孢杆菌中表达的可行性。方法以大肠杆菌和枯草芽孢杆菌的穿梭质粒为基本骨架,在大肠杆菌中完成含有绿色荧光蛋白(GFP)基因的重组表达质粒的构建,通过酶切鉴定筛选阳性克隆,采用电转化的方法,将重组质粒转入枯草芽孢杆菌进行表达,通过检测GFP的存在,评价枯草芽孢杆菌对异源基因的表达。结果重组表达质粒pGJP-GFP酶切鉴定结果与预期片段大小相符。绿色荧光蛋白可在枯草芽孢杆菌中表达,且表达蛋白具有较好的生物学活性。结论利用枯草芽孢杆菌的自身启动子,可以实现外源基因在枯草芽孢杆菌中的表达。     

氨基甲酸乙酯水解酶在枯草芽孢杆菌中的表达及发酵优化

将来源于赖氨酸芽孢杆菌SC02的氨基甲酸乙酯水解酶(UH)基因在枯草芽孢杆菌Bacillus subtilis WB600中进行克隆和表达,在枯草芽孢杆菌中实现了UH活性表达,在摇瓶水平通过单因素考察和响应面分析实验对氨基甲酸乙酯水解酶发酵进行优化. 结表明,酶活最高可达到14.20 U/mL,产酶最佳培养基成分为：淀粉10 g/L、磷酸氢二钾9 g/L、麦芽浸膏25 g/L、硫酸镁1 g/L、胰蛋白胨55 g/L,最适发酵温度为37℃,最佳接种量4%. 在3 L发酵罐中采用最优发酵条件,酶活在16 h达到18.03 U/mL.     

枯草芽孢杆菌联产纳豆激酶和g-聚谷氨酸

利用实验室保存的纳豆激酶生产菌Bacillus subtilis Natto NLSSe进行了g-聚谷氨酸合成研究,在不添加谷氨酸的培养基中合成了分子量在200~300 万Da的g-聚谷氨酸,表明该菌是谷氨酸非依赖型菌. 合成纳豆激酶的合适碳、氮源分别是蔗糖和大豆蛋白胨,合成g-聚谷氨酸的合适碳、氮源分别是柠檬酸和NH4C1. 通过正交实验研究了碳、氮源对纳豆激酶和g-聚谷氨酸联产的影响,结果表明,增加培养基中大豆蛋白胨及柠檬酸的浓度能分别促进纳豆激酶和g-聚谷氨酸的合成,而不抑制另一产物的合成,有利于纳豆激酶和g-聚谷氨酸的联产. 在大豆蛋白胨10 g/L, NH4C1 9 g/L,柠檬酸15 g/L时,纳豆激酶酶活为121.2 U/mL,g-聚谷氨酸产量为1.1 g/L,均达到了单独合成时的水平.     

Stability of silicon nitride heated in air and in carbon monoxide

Conclusions Silicon nitride oxidizes in air at 1100–1500°C mainly with the formation of silica. An addition of NaF contributes to oxidation of the silicon nitride to silicon oxynitride.In a coke filling silicon nitride decomposes at 1450–1550°C into oxynitride and cubic silicon carbide.Additions of CaF₂ and MgO contribute to the conversion of the silicon nitride in a carbon monoxide atmosphere into the silicon oxynitride at 1550°C.Translated from Ogneupory, No.6, pp. 33–39, June, 1967.     

肌酐酶在枯草芽孢杆菌中的异源表达及分泌机制

肌酐酶是用于临床检测肾小球滤过功能的关键酶之一,但目前国内肌酐酶的生产量较低无法满足市场需求,多依赖于国外进口。为了解决这一问题,本研究将恶臭假单胞杆菌肌酐酶基因克隆至原核表达载体pMA5实现肌酐酶在枯草芽孢杆菌1A751中的异源表达。随后通过启动子优化,使肌酐酶的蛋白表达量显著提高到1.08mg/mL,并且胞外肌酐酶的比酶活力达到238U/mg。同时发现肌酐酶可不依赖于信号肽即可实现胞外分泌,因此对肌酐酶在枯草芽孢杆菌中的分泌机制进行研究。通过对经典分泌途径和Holin途径的分析排除、利用Calcein-AM/PI双染色法鉴定表达菌株1AGC的细胞膜不完整,最后通过电子显微镜观察结果表明表达菌株表面存在潜在的泄漏位点,因此证实肌酐酶在枯草芽孢杆菌中通过细胞泄漏的方式,释放到胞外培养基中。本文构建了一株基于细胞泄漏的肌酐酶高产菌株,为肌酐酶的表达和潜在工业化应用提供理论基础,同时也为枯草芽孢杆菌泄漏表达系统提供了一定的研究基础。