雪里蕻腌制中亚硝酸盐含量的实验测定

以冬季10℃以下温度和在37℃恒温中腌制的九头雪里蕻为样品,采用格里斯试剂比色法来测定其亚硝酸盐的含量。实验表明:当在10℃以下时,腌制九头雪里蕻中亚硝酸盐含量在21d前略超国家标准(4 mg/kg);但当在37℃恒温时,亚硝酸盐含量猛增。实验还初步揭示了硝酸还原性细菌是一种兼氧细菌。     

微生物亚硝酸盐还原酶的研究进展

亚硝酸盐还原酶(Nitrite reductase,简称NiR,EC1.7.2.1)是催化亚硝酸盐(Nitrite,简称NIT)还原的一类酶,可降解NIT为NO或NH3,是自然界氮循环过程的关键酶。本文详细阐述亚硝酸盐还原酶的分类、结构特点、催化机制以及现阶段的应用领域,为深入研究亚硝酸还原酶提供参考。     

硝化细菌中亚硝酸盐氧化还原酶的研究进展

亚硝酸盐氧化还原酶(nitrite oxidoreductase,NXR)是硝化细菌将亚硝酸盐氧化为硝酸盐的关键酶,广泛存在于亚硝酸盐氧化菌中.由于它是可溶性的膜内酶,其催化机理与膜内电子传递密切联系,给它的研究带来了一定的困难.本文综述了多年来国内外研究者从不同方面对NXR研究的成果,详细论述了NXR的组成结构、工作机理以及不同因子对其活性的影响,总结了近几年应用于研究NXR的新方法,并展望了对NXR研究的发展方向及其意义.     

一株灰肉红菇内生真菌的分离鉴定及其抑菌活性研究

灰肉红菇（Russula griseocarnosa）是岭南地区著名的野生食药用真菌。本研究通过组织分离的方法,从灰肉红菇子实体分离获得一株内生真菌,经形态学和分子生物学分析鉴定为爪哇虫草（Cordyceps javanica）。以牛津杯抑菌圈法及二倍稀释法测试了其菌丝体胞内和胞外多糖粗提物对金黄色葡萄球菌（Staphylococcus aureus）和铜绿假单胞菌（Pseudomonas aeruginosa）的抑菌活性。结果表明：水溶性胞内、胞外多糖对金黄色葡萄球菌及铜绿假单胞菌均具有抑菌活性,最低抑菌浓度（MIC）为37.5 mg/mL。     

腌制蔬菜微生物的研究进展

对腌制蔬菜微生物的研究进展进行综述,包括腌制原理,腌制过程中的主要微生物和影响微生物的环境因子,以及鉴定微生物的传统方法和基因测序技术,分析了不同鉴定技术的优缺点,为腌制蔬菜微生物研究提供科学依据。     

蔬菜低盐腌制技术的研究进展

综述了低盐腌制蔬菜的研究现状,重点阐述了高盐咸坯脱盐技术和直接低盐腌制技术的研究进展,指出蔬菜低盐腌制技术在现阶段存在的不足,并对其未来的发展前景进行了展望,为低盐腌制蔬菜的研发提供理论借鉴与参考。     

茶多酚对大肠杆菌抑菌机理的研究

茶多酚(tea polyphenols,TP)是一种具有广谱抗菌作用的活性质,以大肠杆菌(Escherichia coli,E.coli)为研究对象,采用牛津杯实验研究茶多酚的最小抑菌浓度,并采用结晶紫实验、电导率测定、离子泄漏测定来分析TP对E.coli细胞膜通透性的影响。通过琼脂糖凝胶电泳分析TP对E.coli DNA的影响。结果显示,TP对E.coli的最小抑菌浓度为40μg/m L;结晶紫实验中,随着浓度的增大,OD590也随之增大;随着处理时间的增长,电导率随之增大,离子泄漏随之增多,说明TP可以作用于E.coli的细胞膜,能够改变其通透性。通过琼脂糖凝胶电泳分析可知TP处理后和空白对照组相比较,DNA条带出现变暗、拖尾现象,说明TP能够作用于E.coli的遗传物质DNA。     

水体中亚硝酸盐积累的生物过程及影响因素研究进展

亚硝酸盐是氮循环过程的中间产物,其积累超过一定量则会抑制微生物的生长与代谢,也会给人与水生生物带来健康风险。而在高氮污水生物脱氮工艺中,持续维持亚硝酸盐的积累能实现短程硝化过程,降低生物脱氮的能耗进而降低运营成本。本文综述了在水环境中亚硝酸盐积累的生物过程与积累原因,并对影响亚硝酸盐积累的因素进行了总结,旨在为提高污水处理过程中氮的去除效率,降低运营成本,减少排放污水及自然水体中亚硝态氮含量提供参考。     

硝酸盐/亚硝酸盐检测方法的研究进展

对国内外硝酸盐与亚硝酸盐的检测方法进行综述。亚硝酸盐定量检测方法有光度法、荧光法、示波极谱法、色谱法,这些方法各有优缺点,目前使用最广的是分光光度法。亚硝酸盐快速检测方法也较多,有检测试纸、粉剂等新型检测方法,这些方法简单、方便,可应用于一些简单的定性检测,但对乳、豆浆等具有屏蔽作用的样品检测效果并不理想,因此建立灵敏、准确的硝酸盐/亚硝酸盐的快速检测方法具有重要的现实意义。     

家蝇抗菌肽的抑菌动力学研究及其机理初探

利用鼠伤寒沙门氏菌针刺诱导家蝇幼虫表达抗菌肽,对抗菌肽的抑菌动力学进行研究,并通过抗菌肽样品对不同细菌动力学特性的研究出发对抗菌肽抑菌作用机制进行探讨。研究发现抗菌肽样品的活性与作用时间有关,24h内出现一到两个活性峰,同一抗菌肽样品对不同细菌的抑菌动力学有差异,抗菌肽的抑菌动力学机制应该与它的的抑菌作用机制有关。通过电镜观测、细胞磷代谢、紫外吸收物测定以及抗菌肽与细菌DNA相互作用结果可知,微生物诱导家蝇表达的抗菌肽样品不仅能够造成细菌细胞的快速坍塌破裂而且能够破坏细胞核心,与DNA结合作用。抗菌肽抑菌动力学的解释：微生物诱导产物中含有两类抗菌肽,一类抗菌肽能造成细胞膜的快速坍塌破裂形成第一个活性峰;另一类抗菌肽可进入细胞,破坏细胞核心,造成紫外吸收物大量外泄形成第二个活性峰。     

Clostridium butyricum ammonifies nitrite, but not nitrate

Abstract Clostridium butyricum strains DSM 552 (ATCC 19398) and ATCC 8260 grow with nitrite and hydroxylamine, but not with nitrate as the sole nitrogen source. Nitrite is largely converted to extracellular ammonium. The nitrite reductases are neither repressed by NH₄⁺ nor induced by NO₂⁻, and are located in the cytoplasm. Methyl viologen and ferredoxin, but not NADH, serve as electron donors. No evidence for a nitrate reductase was found in either strain.     

Simple and rapid method for the measurement of nitrite and nitrate in human plasma and cerebrospinal fluid by capillary electrophoresis

Nitrite and nitrate levels in physiological fluids are commonly used as an index of nitric oxide production. We developed simple and rapid method for the determination of these anions by capillary zone electrophoresis employing borate buffer (pH 10, 100 mmol/l) as running electrolyte. The anions were analyzed in plasma and cerebrospinal fluid (CSF) without deproteinization of the samples. Electrophoresis was carried out in a capillary (36.5 cm×75 μm) at a potential of 15 kV, with on-column UV detection at 214 nm. Mean retention times for nitrite and nitrates were 4.631 and 5.152 min, respectively. The method was linear (r=0.999) within a 1–500 μmol/l concentration range. Physiological levels of nitrate in plasma (40.2 μmol/l) and CSF (15.3 μmol/l) could be determined with good precision (coefficients of variation <6%) and accuracy (recoveries of added nitrate to plasma and CSF were 97.4 and 104.5%, respectively). Measurements of the physiological levels of nitrite in plasma (6.1 μmol/l) and CSF (0.9 μmol/l) were less precise and accurate.     

Ion chromatographic method for simultaneous determination of nitrate and nitrite in human saliva

A simple, rapid, accurate and sensitive method is proposed for the simultaneous determination of nitrite and nitrate in human saliva. Nitrite and nitrate present in the human saliva were determined after 10- to 100-fold dilution with ion chromatography (IC) using suppressed conductivity detection. Recoveries of nitrite and nitrate were found to be ranged between 95% and 101%. The method was linear (r²=0.9991) over the concentration working range. The detection limits were found to be 15.0 μg/l and 33.5 μg/l, for nitrite and nitrate, respectively. Ions that are present in human saliva and several other ions that are suspected to affect nitrite and nitrate determination were checked. It was found that most of the ions did not cause any interference in the determination. The method allows simultaneous determination of nitrite and nitrate in human saliva.     

Gas chromatographic–tandem mass spectrometric quantification of human plasma and urinary nitrate after its reduction to nitrite and derivatization to the pentafluorobenzyl derivative

Gas chromatography–mass spectrometry (GC–MS) of nitrite as its pentafluorobenzyl derivative in the negative-ion chemical ionization mode is a useful analytical tool to quantify accurately and sensitively nitrite and nitrate after its reduction to nitrite in various biological fluids. In the present study we demonstrate the utility of GC–tandem MS to quantify nitrate in human plasma and urine. Our present results verify human plasma and urine levels of nitrite and nitrate measured previously by GC–MS.     

Rapid determination of nitrite by reversed-phase high-performance liquid chromatography with fluorescence detection

Measurement of nitrite and nitrate, the stable oxidation products of nitric oxide (NO), provides a useful tool to study NO synthesis in vivo and in cell cultures. A simple and rapid fluorometric HPLC method was developed for determination of nitrite through its derivatization with 2,3-diaminonaphthalene (DAN). Nitrite, in standard solution, cell culture medium, or biological samples, readily reacted with DAN under acidic conditions to yield the highly fluorescent 2,3-naphthotriazole (NAT). For analysis of nitrate, it was converted to nitrite by nitrate reductase, followed by the derivatization of nitrite with DAN to form NAT. NAT was separated on a 5-μm reversed-phase C₈ column (150×4.6 mm, I.D.) guarded by a 40-μm reversed-phase C₁₈ column (50×4.6 mm, I.D.), and eluted with 15 mM sodium phosphate buffer (pH 7.5) containing 50% methanol (flow-rate, 1.3 ml/min). Fluorescence was monitored with excitation at 375 nm and emission at 415 nm. Mean retention time for NAT was 4.4 min. The fluorescence intensity of NAT was linear with nitrite or nitrate concentrations ranging from 12.5 to 2000 nM in water, cell culture media, plasma and urine. The detection limit for nitrite and nitrate was 10 pmol/ml. Because NAT is well separated from DAN and other fluorescent components present in biological samples, our HPLC method offers the advantages of high sensitivity and specificity as well as easy automation for quantifying picomole levels of nitrite and nitrate in cell culture medium and biological samples.     

Determination of nitrate and nitrite by high-performance liquid chromatography in human plasma

A new, accurate, fast and simple method has been implemented by which nitrite and nitrate ions, as stable forms of nitric oxide production were studied. A study of these two ions was carried out by a sensitive and accurate HPLC method with two detectors. The most important advantages of the reported method are: short time of analysis, minimal sample pre-treatment, long life of the analytical column and stable eluent solution. The photodiode array UV-Vis detector detected nitrite and nitrate ions at an absorbance of 212 nm. Much more sensitive electrochemical detection with a WE (glassy carbon) electrode was used for the detection of nitrite ions. An analytical chromatographic column was formed by a sorbent, containing strong base anion-exchange groups bound in Cl(-) form in the hydrophilic hydroxyethyl methacrylate matrix. The anions were analysed in human plasma without deproteinization using 0.02 M sodium perchlorate monohydrate as eluent solution at pH 3.9. At this pH organic substances do not affect the analysis. The retention times for nitrite and nitrate were 3.62 and 3.72 min (by electrochemical detection) and 4.44 min, respectively. The method was linear (r=0.9992, 0.9998, 0.996) within a 1-100 (nitrate), 1-20 micro mol/l (nitrite) concentration range.     

High-resolution microanalysis of nitrite and nitrate in neuronal tissues by capillary electrophoresis with conductivity detection

Nitrites and nitrates are widely used reporters of endogenous activity of nitric oxide synthases (NOS), an important group of enzymes producing the gaseous signal molecule nitric oxide (NO). However, due to the great chemical heterogeneity of neuronal tissues, standard analytical protocols for evaluation of neuronal nitrite/nitrate concentrations are inefficient. We optimized a high-performance capillary zone electrophoresis (CZE) technique to analyze nitrite/nitrate concentrations in submicroliter samples from mammalian neuronal tissues. The measurements were made using a PrinCE 476 computerized capillary electrophoresis system with a Crystal 1000 contact conductivity detector. Isotachophoretic stacking injection of 1000- to 10000-fold diluted samples, which had been pretreated with a custom-designed solid-phase microextraction (SPME) cartridge, was employed to assay micromolar and nanomolar nitrite and nitrate levels in the presence of the high millimolar chloride concentrations characteristic of many biological samples. In the presented technique, a 10-microl volume of diluted ganglionic sample was used for chloride removal and sample cleanup. The method yields high analytical performance, including good reproducibility, resolution, and accuracy. The limits of detection relative to undiluted sample matrix were 8.9 nM (0.41 ppb) and 3.54 nM (0.22 ppb) for nitrite and nitrate, respectively. In addition, this technique resolves other anions that are present in neuronal tissues at sub-nanomolar concentrations and can be broadly applied for high-throughput anionic profiling. In rat dorsal root ganglia, endogenous levels of nitrate (231+/-29 microM; n=6) and nitrite (24-96 microM) were found. These concentrations exceeded those previously found in neuronal tissue homogenates using different techniques.     

酿酒酵母两种不同嗜杀菌株的比较研究

以酿酒酵母两种不同类型的嗜杀菌株SK4（K1型）和ERRI（K2型）为材料,分析了不同嗜杀酵母的嗜杀特性,两株嗜杀酵母具有相互杀死作用,其嗜杀活性与菌体生长有关。SK4和ERRI的嗜杀质粒的比较表明：M1－dsRNA质粒和M2-dsRNA质粒分子量分别为1．7kb和1．5kb,两株菌的L－dsRNA质粒均为4．0kb。用高温和紫外线处理嗜杀酵母,嗜杀活性随之消失,消除菌中的M－dsRNA质粒也相应消失,嗜杀活性的消除率随菌株和消除剂的不同而变化。实验证明两株菌产生的毒素蛋白的最适嗜杀作用条件不同,最适pH和温度分别为4．8、16℃和4．0、22℃,但两种毒素蛋白均对在对数生长期的敏感细胞作用最显著。