溴甲烷土壤灭菌对大豆苗期根系生长的影响

利用溴甲烷田间土壤灭菌,研究灭菌对正茬、重茬大豆苗期根系生长和产量的影响.试验结果表明,灭菌处理后重茬(连续种植3a)地大豆根系生长良好,根系形态明显改善,总根长、主根长、植株鲜重和根瘤数增加、孢囊线虫孢囊数为0.而灭菌处理后,正茬地大豆根系前期生长受到一定抑制,主根长、总根长、植株鲜重和侧根数有降低的趋势,但随时间推移,抑制幅度降低.溴甲烷处理促进大豆结瘤.灭菌后,重茬大豆与正茬大豆根系生长差异减少.溴甲烷灭菌处理可作为克服大豆连作障碍问题措施之一.     

Failure to decontaminate Glomus clarum NT4 spores is due to spore wall-associated bacteria

 Exposure of spores of Glomus clarum NT4 to solutions of chloramine-T (2.5–10% w/v) for 10–120 min failed to fully decontaminate all spores. Scanning electron microscopy did not show the presence of contaminants on treated spores, but transmission electron microscopy revealed bacterial cells embedded within the outer spore wall layer. Bacteria that remained protected within the spore walls were detected only when the spores were placed on appropriate media. Nutrient agar and tryptic soy agar supported relatively high levels of contaminant growth and were regarded as good media for assessing contamination, whereas the detection of contaminant growth on water agar required prolonged incubation. Contamination and germination of G. clarum NT4 spores following decontamination treatments were dependent on spore age. Generally, lower concentrations of chloramine-T and shorter incubation periods were required to reduce contamination of freshly harvested spores than of mature spores. Exposure to 10% chloramine-T for 120 min was required to reduce the levels of contamination of mature spores to ≤10%. Unfortunately, spore germination was compromised by rigorous decontamination treatments, thus the success of any decontamination procedure should be evaluated prior to its routine use. Moreover, if the interpretation of experimental results rests on the assumption of true surface sterility of VAMF spores, we suggest that the axenic condition of spores be confirmed prior to experimentation on a medium that encourages contaminant growth. Accepted: 12 July 1995     

Reduced fouling and enhanced microbial inactivation during online sterilization of cheese whey using UV coil reactors in series

The effectiveness of coil UV reactor series for the online sterilization of cheese whey was compared to those of the single conventional and coil reactors at various flow rates (5–70 mL/min). The residence time varied from 168 to 12 min and from 48 to 24 min for the single and the series reactors, respectively. Hundred percent destruction efficiency could not be achieved in the single reactors whereas in the coil reactor series the destruction efficiency reached 100% at the flow rates of 35 and 40 mL/min. The rate of microbial destruction was described by polynomial equation for the single coil reactor and by exponential equations for the single conventional reactor and the coil reactor series. The temperature of the effluent decreased with the increase in flow rate in all the reactors. The maximum effluent temperatures in the single conventional reactor, single coil reactor and coil reactor series were 45.8, 46.1, and 36.4 °C (Δt = 20.8, 21.1, 11.4 °C), respectively. The flow in all the reactors was laminar (R _e = 1.39–20.10) and the Dean number was in the range of 1.09–15.41 in the coil reactors. Visual observation revealed less fouling on the UV lamps of coil reactors than on that of the conventional reactor due to the impact of Dean flow. The total operating time during which 100% destruction efficiency is achieved prior to the advent of fouling was 240 min in the coil reactor series compared to only 45 min in the conventional reactor.     

STERILIZATION OF SUSPENDED SEDIMENTS BY GAMMA RADIATION

SUMMARY

Gamma radiation as an alternative sterilization technique for silt and clay suspensions is evaluated. It is compared to autoclaving in regard to sterility and changes in physical and chemical properties of the suspensions. A minimum radiation dose rate of 5 kGy s^?1 led to sterilization and no changes in lattice structure or precipitation of the suspensoids were observed. The adsorbed ionic composition of the silt and clay particles was, however, altered and should be rectified before radiated suspensoids are used. Autoclaving resulted in sterility, but irreversible precipitation of the suspensoids made it less applicable where the colloidal properties of the clay and silt are to be maintained.     

Der einfluss von membranfiltration oder autoklavieren auf die ernte von raphidonema spiculiforme vischer

Through growth experiments with the alga Raphidonema spiculiforme Vischer we have been trying to determine whether with autoclavated or filtrated culture solutions more substantial algal yields could be expected.In mediums rich with nutritive salts we noted essentially more substantial yields in filtered than in autoclavated water. We suppose that in the latter media a part of the growth potential is lost through the formation of poor soluble salts.In mediums poor with nutritive salts the yields were more substantial after autoclavation than after filtration. The principal causes for this observation could be the restraining effect on growth through the adsorption of loaded particles through the filter and the retention of suspended matter enveloped with nutritive salts.

Adresse des Autors: Dr. F. Schanz, Kant. Laboratorium, Fehrenstr. 15, 8030, Zürich     

Biomechanical properties of bovine tendon xenografts treated with a modern processing method

Xenograft tendons have been used in few human studies, with variable results. With the advent of novel tissue processing techniques, which may mitigate against an immune-mediated rejection response without adversely affecting mechanical properties, there may now be a clinical role for xenograft tendons, particularly in knee ligament reconstruction. We hypothesize that ‘BioCleanse®’ processed bovine extensor digitorum medialis (EDM) tendons exhibit favorable time-zero pre-implantation biomechanical characteristics when compared to both unprocessed bovine EDM tendons and BioCleanse® processed human cadaveric allograft tibialis anterior tendons.In this in vitro case controlled laboratory study, three groups of tendons underwent a 5-stage static loading test protocol: 15 BioCleanse^® bovine (BCB), 15 fresh frozen unprocessed bovine (FFB), and 12 BioCleanse^® human allograft (BCA) tendons. Cross-sectional area of the grafts was measured using an alginate molding technique, and tendons were mounted within an Instron^® 5565 Materials Testing System using cryogenic clamps.BCB tendons displayed a higher ultimate tensile stress (p<0.05), with equivalent ultimate failure load, creep, and modulus of elasticity when compared to the FFB tendons (p>0.05). BCB tendons had an equivalent cross-sectional area to the BCA tendons (p>0.05) whilst exhibiting a greater failure load, ultimate tensile stress, less creep and a higher modulus of elasticity (p<0.05).The BioCleanse^® process did not adversely affect the time-zero biomechanical properties of bovine xenograft EDM tendons. BioCleanse^® processed bovine xenograft EDM tendons exhibited superior biomechanical characteristics when compared with BioCleanse^® processed allograft tibialis anterior tendons. These findings support further investigation of xenograft tendons in orthopedic soft tissue reconstructive surgery.     

Analysis of survival rates and cellular fatty acid profiles of Listeria monocytogenes treated with supercritical carbon dioxide under the influence of cosolvents

In the present study, we identified several process variables that significantly affect the efficiency of supercritical carbon dioxide inactivation of the food-borne pathogen Listeria monocytogenes. Treatment with SC-CO(2) completely disabled the colony-forming activity of the cells (8-log reduction) within specific treatment time (10-50 min), pressure (80-150 bar), and temperature ranges (35-45 degrees C). Microorganism inactivation rates increased proportionally with pressure and temperature, but the inactivation rate decreased significantly when cells were suspended in phosphate-buffered saline rather than in physiological saline. Additionally, when the microbial cell suspension was 80-100% (w/w) of water, the SC-CO(2)-mediated reduction in CFU ml(-1) was 4-8 log higher at the same treatment conditions than in typical cell suspensions (a water content of 800-4000% [w/w]) or dry preparations that had only 2-10% (w/w) of water. The addition of a fatty acid, oleic acid, decreased the effectiveness of the microbial inactivation by SC-CO(2), but the addition of a surfactant, sucrose monolaurate, increased the effectiveness. Therefore, cosolvents for SC-CO(2), including water, a fatty acid, and a surfactant in this study, were found to greatly influence on the inactivation effectiveness. The extraction of cellular substances, such as nucleic acid- and protein-like materials and fatty acids, was monitored by spectrophotometry and GC/MS and increased with SC-CO(2) treatment time. Additionally, using scanning and transmission electron microscopies, we investigated morphological changes in the SC-CO(2)-treated cells. The effects of the variables we have described herein represent a significant contribution to our current knowledge of this method of inactivating food-borne pathogens.     

一种以黄化法为基础提高毛白杨快速繁殖效率的新方法

本文报道以黄化法为基础的毛白杨(Populus tomentosa)快速繁殖方法的初步研究结果。它包括1.用低浓度的先锋霉素(cefotaxime 2.5ppm)抑制快速繁殖过程中的细菌污染和用低浓度 HgCl_2灭菌的方法恢复经长期继代培养后被污染的试管植物;2.用极低浓度的 TDZ(thidiazuron 0.005ppm)替代价格昂贵的玉米素(zeatin,Z),促进毛白杨叶外植体上芽的分化和增殖;3.用黄化的方法促使芽的伸长以增加可被用于生根的嫩枝的数量。用这种方法可在一个100ml 的三角瓶中得到约50个黄化的嫩枝,比在光下培养得到的嫩枝多3—5倍;4.黄化嫩枝直接扦插或经光下转绿后扦插于经灭菌的基质中,生根率均可达到90%以上。这一方法可以节省人力和能耗,提高培养室的利用效率,大幅度地提高快速繁殖的效率。     

高压电场灭菌效果研究

本文以乳酸杆菌、枯草杆菌及酵母菌为研究对象,研究了高压交流电场作用对它们的致死率影响及细胞结构的变化。实验表明：在22．5kv／cm的场强下处理ls能导致乳酸杆菌活菌数降低近6个数量级,通过显微摄影可明显观察到枯草杆菌细胞结构的破裂和酵母细胞的死亡。     

臭氧对真菌杀灭作用的初步研究

以根霉 ,黑曲霉 ,青霉 ,酵母菌等为研究对象 ,测定了放电时间与致死率的曲线关系 ,并观察了与空白对照后其菌落形态的变化。实验结果表明 ,随着放电时间的增长 ,致死率明显升高 ,且能够达到完全杀菌。