好氧反硝化细菌及其在微污染水源水修复中的应用研究进展

相比于氨氮,天然水体中的硝酸盐氮通常更稳定,导致更难将其从水中去除。由于好氧反硝化可以在有氧环境下进行反硝化作用去除硝酸盐氮,该过程对含有较高溶解氧的天然水体中硝酸盐氮处理有重要作用。本文综述了好氧反硝化菌的分离纯化现状、微生物代谢机制和环境影响因子,并介绍了功能菌群在微污染饮用水源水生物修复的应用研究进展。与一般的厌氧反硝化类似,好氧反硝化菌的种属分布较广,常见的如假单胞菌属(Pseudomoas)、产碱杆菌属(Alcaligenes)、副球菌属(Paracoccus)和芽孢杆菌属(Bacillus)等所属部分微生物均有好氧反硝化能力。大部分好氧反硝化菌株在最佳生长条件下(25–37℃、溶解氧浓度为3–5mg/L、pH为7–8、碳氮比为5–10)具有高效的脱氮效率。但目前好氧反硝化作用在微污染饮用水源水的生物修复方面的应用仍有着脱氮性能不稳定、菌剂流失等不足。此外,目前较少相关中试及实际工程应用的研究,需要进一步的深入探究。     

Crop responses to CO2 enrichment

Carbon dioxide is rising in the global atmosphere, and this increase can be expected to continue into the foreseeable future. This compound is an essential input to plant life. Crop function is affected across all scales from biochemical to agro-ecosystem. An array of methods (leaf cuvettes, field chambers, free-air release systems) are available for experimental studies of CO₂ effects. Carbon dioxide enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are markedly altered. Interactions between CO₂ and environmental factors that influence plants are known to occur. Implications for crop growth and yield are enormous. Strategies designed to assure future global food security must include a consideration of crop responses to elevated atmospheric CO₂. Future research should include these targets: search for new insights, development of new techniques, construction of better simulation models, investigation of belowground processes, study of interactions, and the elimination of major discrepancies in the scientific knowledge base.     

切除上胚轴对绿豆子叶衰老逆转及其核酸和蛋白质代谢的效应

在绿豆子叶衰老达到不归点(萌发后5～6d)前切除上胚轴可使开始衰老的子叶中核酸和蛋白质含量回升,衰老短期逆转。衰老不归点后的子叶中核酸和蛋白质变化的主要特征是:丧失了较多的核主带DNA、25S、18S rRNA以及大部分可溶性蛋白质组分,一种小分子DNA 组分完全消失。不归点前切除上胚轴可使上述核酸和蛋白质组分明显增加,表明子叶衰老的逆转可能与这些重要功能物质的回升有关。在切除上胚轴的茎顶涂抹IAA,能阻止子叶核酸和蛋白质回升,也消除了切除上胚轴对子叶裹老的逆转作用。     

Upper thermal limits predict herpetofaunal responses to forest edge and cover

Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CT_max) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CT_max occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CT_max are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material.     

Rhizosphere effect of nanoscale zero-valent iron on mycorrhiza-dependent maize assimilation

Rhizosphere effect of nanoscale zero-valent iron (nZVI) is crucial but little reported. Maize seeds were dressed with four nZVI concentrations (0, 1.0, 1.5, 2 g kg⁻¹) and inoculated with arbuscular mycorrhizal fungus (AMF) (Funneliformis mosseae). The SEM images illuminated that excessive nZVI particles (2 g kg⁻¹) were agglomerated on the surface of hyphae and spore, causing severe deformation and inactivation of AMF symbionts and thereafter inhibiting water uptake in maize seedlings. This restrained the scavenging effects of enzymatic (superoxide dismutase, peroxidase) and non-enzymatic compounds (proline & malondialdehyde) on ROS, and leaf photoreduction activity and gas exchange ability (p < 0.05). Interestingly, the inoculation with AMF effectively alleviated above negative effects. In contrast, appropriate dose of nZVI, that is, ≤1.5 g kg⁻¹, can be evenly distributed on the hyphae surface and form the ordered symbionts with AMF. This help massively to enhance hyphae growth and water and nutrient uptake. The enhanced mycorrhizal infection turned to promote rhizosphere symbiont activity and leaf Rubisco and Rubisco activase activity. Light compensation point was massively lowered, which increased photosynthetic carbon supply for AMF symbionts. Particularly, such priming effects were evidently enhanced by drought stress. Our findings provided a novel insight into functional role of nZVI in agriculture and AMF-led green production.     

Matrix synthesis of chiral carboxy derivatives: Aldehyde chiral discrimination due to a two-point coordination of Mg2+

To control stereoselectivity in aldol-like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg²⁺ -protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two-point coordination between Mg²⁺ and potential cation-binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo-selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley-Liss, Inc.     

A carbon-13 nuclear magnetic resonance investigation of the metabolic fluxes associated withy glucose metabolism in human erythrocytes

We have used [2-¹³C]d-glucose and carbon-13 nuclear magnetic resonance (NMR) spectroscopy to investigate metabolic fluxes through the major pathways of glucose metabolism in intact human erythrocytes and to determine the interactions among these pathways under conditions that perturb metabolism. Using the method described, we have been able to measure fluxes through the pentose phosphate pathway, phosphofructokinase, the 2,3-diphosphoglycerate bypass, and phosphoglycerate kinase, as well as glucose uptake, concurrently and in a single experiment. We have measured these fluxes in normal human erythrocytes under the following conditions: (1) fully oxygenated; (2) treated with methylene blue; and (3) deoxygenated. This method makes it possible to monitor various metabolic effects of stresses in normal and pathological states. Not only has ¹³C-NMR spectroscopy proved to be a useful method for measuring in vivo flux through the pentose phosphate pathway, but it has also provided additional information about the cycling of metabolites through the non-oxidative portion of the pentose phosphate pathway. Our evidence from experiments with [1-¹³C]-, [2-¹³C]-, and [3-¹³C]d-glucoses indicates that there is an observable reverse flux of fructose 6-phosphate through the reactions catalyzed by transketolase and transaldolase, even in the presence of a net flux through the pentose phosphate pathway.     

Metropolis Monte Carlo calculations of DNA structure using internal coordinates and NMR distance restraints: An alternative method for generating a high-resolution solution structure

Summary A new method, a restrained Monte Carlo (rMC) calculation, is demonstrated for generating high-resolution structures of DNA oligonucleotides in solution from interproton distance restraints and bounds derived from complete relaxation matrix analysis of two-dimensional nuclear Overhauser effect (NOE) spectral peak intensities. As in the case of restrained molecular dynamics (rMD) refinement of structures, the experimental distance restraints and bounds are incorporated as a pseudo-energy term (or penalty function) into the mathematical expression for the molecular energy. However, the use of generalized helical parameters, rather than Cartesian coordinates, to define DNA conformation increases efficiency by decreasing by an order of magnitude the number of parameters needed to describe a conformation and by simplifying the potential energy profile. The Metropolis Monte Carlo method is employed to simulate an annealing process. The rMC method was applied to experimental 2D NOE data from the octamer duplex d(GTA-TAATG)·d(CATTATAC). Using starting structures from different locations in conformational space (e.g. A-DNA and B-DNA), the rMC calculations readily converged, with a root-mean-square deviation (RMSD) of <0.3 Å between structures generated using different protocols and starting structures. Theoretical 2D NOE peak intensities were calculated for the rMC-generated structures using the complete relaxation matrix program CORMA, enabling a comparison with experimental intensities via residual indices. Simulation of the vicinal proton coupling constants was carried out for the structures generated, enabling a comparison with the experimental deoxyribose ring coupling constants, which were not utilized in the structure determination in the case of the rMC simulations. Agreement with experimental 2D NOE and scalar coupling data was good in all cases. The rMC structures are quite similar to that refined by a traditional restrained MD approach (RMSD<0.5 Å) despite the different force fields used and despite the fact that MD refinement was conducted with additional restraints imposed on the endocyclic torsion angles of deoxyriboses. The computational time required for the rMC and rMD calculations is about the same. A comparison of structural parameters is made and some limitations of both methods are discussed with regard to the average nature of the experimental restraints used in the refinement.Abbreviations MC Monte Carlo - rMC restrained Monte Carlo - MD molecular dynamics - rMD restrained molecular dynamics - DG distance geometry - EM energy minimization - 2D NOE two-dimensional nuclear Overhauser effect - DQF-COSY double-quantum-filtered correlation spectroscopy - RMSD root-mean-square deviation To whom correspondence should be addressed.     

信号分子在生物脱氮中的作用及检测方法

生物脱氮是由微生物主导的地球氮循环中的重要环节之一,主要包括硝化、反硝化和厌氧氨氧化(anaerobic ammonium oxidation,anammox)等过程。在微生物联合作用下,污水中的有机氮及氨氮经一系列作用转化为氮气,这种经济高效、环境友好的处理工艺在世界范围内得到广泛应用。群体感应(quorum sensing,QS)以信号分子为媒介通过改变菌群密度和周围环境变化来调节微生物的各种行为。大量的研究已证实调控QS信号分子在生物脱氮中具有应用潜力。本文介绍了各种信号分子类型,从基因组学、实际应用等方面综述了各类信号分子以及检测方法,同时针对酰基高丝氨酸内酯(acyl homoserine lactones,AHLs)类信号分子在生物脱氮中的作用进行详细介绍。然而不足之处在于信号分子研究只是停留在实验室阶段,仅仅研究了单一信号分子对生物脱氮的影响。未来可将信号分子应用于实际污水,研究多种信号分子共同作用以及多种微生物之间的QS现象。     

In Vitro and Molecular Docking Evaluation of Larvicidal Effects of Essential Oils of Five Aromatic Plants on the Fall Armyworm Spodoptera frugiperda JE. Smith (Lepidoptera: Noctuidae) from Ivory Coast

Faced with the serious consequences resulting from the abusive and repeated use of synthetic chemicals, today rethinking crop protection is more than necessary. It is in this context that the essential oils of the Lamiaceae Ocimum gratissimum and Ocimum canum, the Poaceae Cymbopogon citratus and nardus and a Rutaceae Citrus sp. of known chemical compositions were experimented. The evaluation of the larvicidal potential of the essential oils was done by the method of topical application of the test solutions, on the L1−L2 stage larvae from the first generation of S. frugiperda obtained after rearing in an air-conditioned room. Lethal concentrations (LC₁₀, LC₅₀ and LC₉₀) were determined after 48 h. After assessing the larvicidal potential of essential oils, molecular docking was carried out to study protein-ligand interactions and their propensity to bind to insect enzyme sites (AChE). The essential oil of O. gratissimum was the most effective with the lowest lethal concentrations (LC₁₀=0.91 %, LC₅₀=1.91 % and LC₉₀=3.92 %). The least toxic oil to larvae was Citrus sp. (LC₁₀=5.44 %, LC₅₀=20.50 % and LC₉₀=77.41 %). Molecular docking revealed that p-cymene and thymol from O. gratissimum essential oil are structurally similar and bind to the AChE active site via predominantly hydrophobic interactions and a H-bond with Tyr374 in the case of thymol. The essential oil of O. gratissimum constitutes a potential candidate for the development of biological insecticides for the fight against insect pests and for the protection of the environment.