近零磁场对拟南芥生长发育影响初探及趋磁细菌(Magnetospirillum magneticum）铁还原酶基因 MmFre 的克隆和功能分析

地磁场伴随着生命的起源、发生和进化，地球上的一切生命无时无刻不处于地球磁场中。地球自诞生以来，地磁场的强度一直在细微变化，但地磁场强度减弱会对植物产生什么样的直接影响尚知之甚少。随着对太空探索的不断发展，人类越来越需要了解处于零磁场环境的太空中生物的适应性。近零磁场是地磁场的恒定组分降低为零或者接近零的空间。本论文利用近零磁场环境探索了地磁场减弱对拟南芥整个生长周期的影响，开展了近零磁场下拟南芥短期生长试验，主要包括种子的萌发、暗培养、根生长、幼苗鲜重和根向重性分析，以及对近零磁场下拟南芥整个生长周期的表型进行了观察统计分析。结果发现(1)无论在光照还是暗培养的环境中，近零磁场对拟南芥种子的萌发、幼苗根的伸长、鲜重变化以及根向重性等的影响较小。(2)对拟南芥整个生长周期过程中表型变化进行的观察和统计分析发现：近零磁场环境中，拟南芥可以完成正常的生活史;但植株开花时间推迟、开花持续时间延长、枝条数减少、植株高度受到了抑制，种子千粒重降低。表明近零磁场对拟南芥营养生长的影响较小，而对生殖生长的影响较明显，暗示地磁场作为环境因子可能参与影响植物的生殖生长。 趋磁细菌(Magnetospirillum magneticum)是一种可以沿磁力线方向运动的特殊的细菌，其胞内铁含量是菌体干重的3％，是非磁性细菌的数百倍，其中的铁主要以Fe3O4/Fe3S4 形式存在于磁小体(magnetosome) 中。趋磁细菌主要通过分泌转铁载体吸收环境中的三价铁。在磁小体合成过程中，三价铁还原为二价是一个必需的过程，因而铁还原酶在趋磁细菌的铁还原过程中可能起着重要的作用。我们以趋磁细菌AMB-1 为材料，克隆了预测的铁还原酶基因，命名为MmFre ，并在内源铁还原酶活性较低的酵母突变株S288C fre1 fre2 中进行异源超表达，对其铁还原活性进行了初步分析;同时结合GFP 融合蛋白技术对该基因的表达产物进行了酵母的亚细胞定位。结果表明：(1)利用生物信息学分析发现，MmFre 基因编码区含有1335 bp，编码444 个氨基酸残基;氨基酸序列中含有一个FAD 结合位点，并具有6 个跨膜结构域;(2)该基因在酵母表达后利用酵母活体进行酶活性检测发现，其铁还原酶活性是对照组的4 倍，暗示该基因在真核生物中的表达产物可以执行铁还原的功能;(3)利用激光共聚焦显微镜观察发现该基因的表达产物与GFP 构成的融合蛋白广泛的定位在细胞的膜上。因而，MmFre 基因的表达产物确实具有铁还原酶活性，且没有膜特异性分布，其对趋磁细菌磁小体生物合成中铁的还原可能起着重要作用。

Coagulation removal of melanoidins from biologically treated molasses wastewater using ferric chloride

The pigments (melanoidins) in molasses wastewater are refractory to conventional biological treatment. Ferric chloride was used as coagulant to remove color and chemical oxygen demand (COD) from molasses effluent. Using jar test procedure, main operating conditions such as pH and coagulant dosage were investigated. Under the optimum conditions, up to 86% and 96% of COD and color removal efficiencies were achieved. Residual turbidity in supernatant was less than 5 NTU and Fe3+ concentration was negligible because of effective destabilization and subsequent sedimentation. The results of high performance size exclusion chromatography (HPSEC) show that low molecular weight (MW) fraction of melanoidins is more reactive than high MW fraction and increase in the concentration of the lowest MW organic group is related to the capacity of charge neutralization. Aggregate size measurement reveals the size effect on the settleability of flocs formed, with larger flocs settling more rapidly. Charge neutralization and co-precipitation are proposed as predominant coagulation mechanism under the optimum conditions. (C) 2009 Elsevier B.V. All rights reserved.

Hydrolysis and coagulation behavior of polyferric sulfate and ferric sulfate

The hydrolysis behaviors of polyferric sulfate (PFS) and ferric sulfate (FS) under conditions similar to raw wastewater were investigated and the coagulation of biologically pretreated molasses wastewater using PFS and FS was evaluated by studying coagulation efficiency, zeta potential and microscopic surface morphology of flocs. Experimental results show that the hydrolysis behavior of PFS is different from that of FS on the basis of ferron assay. In the case of FS, fast-reacting Fe(III) polymers were the dominant polynuclear species while large fraction of slow-reacting iron polymers is present in PFS. Despite slightly fewer dosages of PFS required as compared to FS, there is no marked difference in the coagulation of molasses effluent between PFS and FS, especially at the optimum dosages. Both coagulants destabilize organic compounds predominantly through charge neutralization-precipitation mechanism. Hydrolysis rate of PFS in synthetic solution is appreciably different from that in raw wastewater. This may due to the effect of sulfate anion introduced as counter-ion as well as depolymerization of larger polymeric Fe(III) species by the organic ligands present in molasses effluent.

EFFECTS OF IRON ON PHYSIOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF Microcystis wesenbergii (Kom.) Kom. (Cyanobacterium)

Iron is an essential trace element for biological requirements of phytoplankton. Effects of iron on physiological and biochemical characteristics of Microcystis wesenbergii were conducted in this study. Results showed that 0.01 mu M [Fe3+] seriously inhibited growth and chlorophyll synthesis of M. wesenbergii, and induced temporary increase of ATPase activities, however, NR. ACP and ALP activities were restrained by iron limitation. Interestingly, iron addition on day 8 resulted in the gradual restoration of structures and functions of above enzymes and resisted a variety of stresses from iron limitation. M. wesenbergii in 10 mu M [Fe3+] treatment group grew normally. enzymes maintained normal levels, and residual phosphate contents in cultures first sharply decreased, then smoothly as M. wesenbergii has a characteristic of luxury consumption of phosphorus. Above parameters in 100 mu M [Fe3+] treatment group were almost same with those in 10 mu M [Fe3+] treatment group except for NR, ACP and ALP activities. In 100 mu M [Fe3+] treatment group, activities of ACP and ALP had temporary increase because phosphate and ferric iron could form insoluble compound - ferric phosphate (Fe3PO4) through adsorption effect. resulting in lack of bioavailable phosphate in culture media. The experiment suggested that too low or too high iron can affect obviously physiological and biochemical characteristics of M. wesenbergii.

Photodegradation of 2-naphthol in aqueous solutions in the presence of humic acid and ferric ions

In this work, the photodegradation of the carcinogenic pollutant 2-naphthol in aqueous solution containing Aldrich humic acid (HA) and ferric ions (Fe(III)) under 125 W and 250 W high pressure mercury lamp (HPML, lambda >= 365 nm) irradiation was investigated. The photooxidation efficiencies were dependent on the pH values, light intensities and Fe(III)/HA concentration in the water, with higher efficiency at pHs 3-4, and 50 mu mol l(-1) Fe(III) with 20 mg l(-1) HA under 250 W HPML. The initial rate of photooxidation increases with increasing, the initial concentration of 2-naphthol from 10 mu mol l(-1) to 100 mu mol l(-1), while do not change at 50 and 100 mu mol l(-1). However, higher removal efficiency of 2-naphthol is achieved at its lower initial concentration of 10 mu mol l(-1), and initial rate of photooxidation is 0.193 mu mol l(-1) min(-1). Dissolved oxygen (DO) plays an important role in the system containing Fe(III)-HA complexes in which Fenton and photo-Fenton reactions were enhanced in the environment. Hydroxyl radicals produced in HA solution with or without ferric ions were determined by using benzene as free radical scavenger and phenol as scavenging products proportional to hydroxyl radicals. By using UV-Vis and excited fluorescence spectrum techniques, the main photooxidation products, which have higher absorption in the region of 240-340 nm, were found, and the mechanisms for the oxidative degradation is proposed.