Cell surface engineering of microorganisms towards adsorption of heavy metals

Abstract

Heavy metal contamination has become a worldwide environmental concern due to its toxicity, non-degradability and food-chain bioaccumulation. Conventional physical and chemical treatment methods for heavy metal removal have disadvantages such as cost-intensiveness, incomplete removal, secondary pollution and the lack of metal specificity. Microbial biomass-based biosorption is one of the approaches gaining increasing attention because it is effective, cheap, and environmental friendly and can work well at low concentrations. To enhance the adsorption properties of microbial cells to heavy metal ions, the cell surface display of various metal-binding proteins/peptides have been performed using a cell surface engineering approach. The surface engineering of Gram-negative bacteria, Gram-positive bacteria and yeast towards the adsorption of heavy metals are reviewed in this article. The problems and future perspectives of this technology are discussed.     

甘肃民乐黄芪品质与土壤关系的研究

目的 研究甘肃民乐黄芪品质与土壤的关系。方法 采集黄芪药材和土壤样品,利用高效液相色谱法、紫外分光光度法、原子吸收分光光度法等测定药材质量、土壤因子及重金属元素。结果 民乐黄芪质量符合药典标准规定,受重金属污染风险低。浸出物与速效钾呈显著负相关;黄芪甲苷与速效钾呈显著正相关;毛蕊异黄酮葡萄糖苷与可溶盐呈极显著正相关,与速效钾呈显著正相关,与pH值呈显著负相关。其中,土壤pH值是影响黄芪浸出物、黄芪甲苷、毛蕊异黄酮葡萄糖苷三者含量的关键因素,其次为全磷、有机质和全氮。结论 研究结果揭示了土壤因子是民乐黄芪品质的主要影响因素,可为民乐县规范化种植黄芪药材提供理论依据。     

乙酸钙的纯化工艺

碳酸钙和冰乙酸在水中反应得到乙酸钙溶液,室温下加入约2.5倍体积的95%乙醇,静置2~4 h,以300目滤布挤压过滤,滤液浓缩后重复操作1次,合并2次所得乙酸钙,80℃热风循环干燥3 h,即得乙酸钙纯品,收率可达82%以上。本工艺产品中镁含量大大降低,质量指标符合美国药典(USP40)要求。     

直接蛋白沉淀-超高效液相色谱法测定氟尿嘧啶血药浓度

建立直接蛋白沉淀-超高效液相色谱法测定血浆中微量氟尿嘧啶的方法。以6%高氯酸为沉淀剂,5-氯尿嘧啶为内标物,样品经涡旋振荡等处理后,高速离心获取上清液作为供试液。供试液测定采用Acquity HSS T₃色谱柱,水-乙腈为流动相,流速为0.2 mL/min,进样量为5 μL,柱温为20 ℃。方法的专属性、准确度、精密度、线性等指标经验证后完全符合定量测定要求,与传统的测定方法相比,可显著缩短进样分析时间、降低试剂成本。本方法已经被成功用于临床病人的血药浓度检测,具有良好的临床应用前景。     

六味地黄汤水提醇溶部位对2型糖尿病大鼠胰岛及肾脏组织形态结构的影响

目的 研究六味地黄汤水提醇溶部位对2型糖尿病大鼠胰岛及肾脏的影响.方法 采用高糖、高脂饲料喂养4周后,再行腹腔注射小剂量链脲佐菌素(STZ)且空腹血糖(FBG)≥16.7 mmol/L的大鼠建立2型糖尿病动物模型,将其随机分为空白组、模型组、罗格列酮组和六味地黄汤水提醇溶部位组,观察给药1个月后大鼠空腹血糖(FBG)和大鼠胰岛、肾脏组织的形态结构.结果 六味地黄汤水提醇溶部位能降低2型糖尿病大鼠FBG值(P＜0.01),对其受损的胰岛及肾脏有修复作用.结论 六味地黄汤水提醇溶部位能够修复2型糖尿病大鼠的胰岛及肾脏,胰岛及肾脏是具干预2型糖尿病作用的靶位之一.     

Impaired participation of potassium channels and Na+/K+‐ATPase in vasodilatation due to reduced nitric oxide bioavailability in rats exposed to mercury

Mercury intoxication is a public health risk factor due to its hazardous effect to several organs, including the cardiovascular system. There is evidence of endothelial dysfunction after exposure to mercury, but the effects on endothelium‐dependent vasodilatation are still unknown. In the present study, we aimed to evaluate the chronic effects of high HgCl₂ doses on the mechanisms of vasodilatation. Wistar rats were injected with HgCl₂ (1st dose 10.86 μg/kg, and daily doses 0.014 μg/kg for 30 days i.m.), and saline was used as control. Mercury exposure reduced the acetylcholine‐induced vasodilatation in aortic rings, which was restored by incubation with antioxidant tiron. Inhibition of the NO synthase, Na⁺/K⁺‐ATPase and K⁺ channels indicates reduced participation of these factors. In the mercury group, there were an increased local anion superoxide and a reduced NO. The vasodilatation to exogenous NO was partially inhibited by co‐incubation with TEA plus tiron, suggesting that reduced NO bioavailability is the responsible to that decreased the participation of K⁺ channels. Moreover, there was an increased participation of the Na⁺/K⁺‐ATPase associated with an up‐regulation of its alpha‐1 subunit. In conclusion, reduced NO bioavailability plays a major role in the impaired participation of K⁺ channels and Na⁺/K⁺‐ATPase in the acetylcholine‐mediated relaxation, although sodium pump is up‐regulated probably as a compensatory mechanism.     

Emergence of superconductivity in heavy-electron materials

Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy-electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at temperature T_c that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors, where phonons provide the pairing glue. Here we propose such a model: a phenomenological BCS-like expression for T_c in heavy-electron materials that is based on a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction and reflects the unusual properties of the heavy-electron normal state from which superconductivity emerges. We show that it provides a quantitative understanding of the pressure-induced variation of T_c in the “hydrogen atoms” of unconventional superconductivity, CeCoIn₅ and CeRhIn₅, predicts scaling behavior and a dome-like structure for T_c in all heavy-electron quantum critical superconductors, provides unexpected connections between members of this family, and quantifies their variations in T_c with a single parameter.Because the unconventional superconductivity found in many heavy-electron materials arises at the border of antiferromagnetic long-range order, it is natural to consider the possibility that its physical origin is its proximity to a quantum critical point that marks a transition from localized to itinerant behavior, and that the associated magnetic quantum critical spin fluctuations provide the pairing glue (1–5), in contrast to conventional superconductors, where phonons provide the pairing glue (6). However, developing a simple physical picture for the behavior of such quantum critical superconductors, including a Bardeen, Cooper, and Schrieffer (BCS)-like expression for their superconducting transition temperature (T_c), has proven difficult. In part, this is because of the unusual normal state from which superconductivity emerges (7–12), and in part it stems from the difficulty in finding a simple model for an effective frequency-dependent attractive quasiparticle interaction that closely resembles that proposed earlier for the cuprates (13–17).In finding a way to characterize heavy-electron quantum critical superconductivity it is helpful to begin by recalling the principal features of its remarkably similar emergence in two of the best-studied materials, CeCoIn₅ and CeRhIn₅ (18–23). As may be seen in Fig. 1, there are three distinct regions of emergent heavy-electron superconductivity in their pressure–temperature phase diagrams that are defined by a line marking the delocalization cross-over temperature, T_L, at which the collective hybridization of the local moments becomes complete and the Néel temperature, T_N, that marks the onset of long-range antiferromagnetic order of the hybridized local moments.Open in a separate windowFig. 1.A phase diagram for heavy-electron superconductors. In region I, only itinerant heavy electrons exist below T_L owing to complete hybridization of the f-moments with background conduction electrons; in region II, collective hybridization is not complete so that heavy electrons coexist with partially hybridized local moments; in region III, these residual moments order antiferromagnetically (AF) at T_N and the surviving heavy electrons become superconducting (SC) at a lower temperature, T_c. The coupling of heavy electrons to the magnetic spin fluctuations emanating from the QCP is responsible for the superconductivity in all regions.Region I: T_c ≤ T_L. Superconductivity emerges from a fully formed heavy-electron state. The general increase in T_c seen with decreasing pressure is cut off by a competing state, quasiparticle localization, so T_c reaches its maximum value at the pressure, p_L, at which the superconducting and localization transition lines intersect.Region II: T_c > T_L and T_N. Superconductivity emerges from a partially formed heavy-electron state whose ability to superconduct is reduced by the partially hybridized local moments with which it coexists. The region includes the quantum critical point (QCP) at T = 0 that marks a zero temperature transition from a state with partially localized ordered behavior to one that is fully itinerant; this QCP is the origin of the quantum critical spin fluctuations that provide the pairing glue in all three regions (2).Region III: T_c ≤ T_N. Partially hybridized local moments are present in sufficient number to become antiferromagnetically ordered at the Néel temperature T_N despite the presence of coexisting remnant heavy electrons that become superconducting at lower temperatures.The dominance of superconductivity around the QCP supports the idea that the coupling of quantum critical spin fluctuations to the heavy-electron quasiparticles plays a central role, with the resulting induced attractive quasiparticle interaction being maximally effective near it. Importantly, there is direct experimental evidence that these quantum critical fluctuations provide the superconducting glue: Curro et al. (4) find that the spin-lattice relaxation rate, 1/T₁, to which these give rise, scales with T_c at the pressure at which T_c is maximum, whereas a recent detailed investigation of that scaling (5) explains how this comes about. First, at this “optimal” pressure, T_c scales with the coherence temperature, T*, that marks the initial emergence of heavy-electron behavior and is determined by the nearest-neighbor exchange interaction between the f-electron local moments (8); second, at this optimal pressure, 1/T₁ scales with T*, a scaling behavior that is a unique signature of its origin in quantum critical spin fluctuations.In this paper we use these important scaling results to develop a simple BCS-like phenomenological expression for the superconducting transition temperature, show that it explains the variation of T_c with pressure for both CeCoIn₅ and CeRhIn₅, and offer a detailed prediction for a similar dome-like structure in other quantum critical heavy-electron superconductors.     

Direct evidence for a magnetic f-electron–mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5

To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn₅. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn₅ then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism.Superconductivity of heavy fermions is of abiding interest, both in its own right (1–7) and because it could exemplify the unconventional Cooper pairing mechanism of high-temperature superconductors (8–11). Heavy-fermion compounds are intermetallics containing magnetic ions in the 4f- or 5f-electronic state within each unit cell. At high temperatures, each f-electron is localized at a magnetic ion (Fig. 1A). At low temperatures, interactions between f-electron spins (red arrows Fig. 1A) lead to the formation of a narrow but the subtly curved f-electron band εkf near the chemical potential (red curve, Fig. 1B), and Kondo screening hybridizes this band with the conventional c-electron band εkc of the metal (black curve, Fig. 1B). As a result, two new heavy-fermion bands Ekα,β (Fig. 1C) appear within a few millielectron volts of the Fermi energy. Their electronic structure is controlled by the hybridization matrix element s_k for interconversion of conduction c-electrons to f-electrons and vice-versa, such thatEkα,β=εkc+εkf2±(εkc−εkf2)2+sk2.[1]The momentum structure of the narrow bands of hybridized electronic states (Eq. 1 and Fig. 1C, blue curves at left) near the Fermi surface then directly reflects the form of magnetic interactions encoded within the parent f-electron band εkf. It is these interactions that are conjectured to drive the Cooper pairing (1–5) and thus the opening up of a superconducting energy gap (Fig. 1C, yellow curves at right).Open in a separate windowFig. 1.Effects of f-electron magnetism in a heavy-fermion material. (A) The magnetic subsystem of CeCoIn₅ consists of almost localized magnetic f-electrons (red arrows) with a weak hopping matrix element yielding a very narrow band with strong magnetic interactions between the f-electron spins. (B) The heavy f-electron band is shown schematically in red and the light c-electron band in black. (C) On the left, schematic of the result of hybridizing the c- and f-electrons in B into new composite electronic states referred to as heavy fermions (blue). On the right, the opening of a superconducting energy gap is schematically shown by back-bending bands near the chemical potential. The microscopic interactions driving Cooper pairing of these states, and thus of heavy-fermion superconductivity, have not been identified unambiguously for any heavy-fermion compound.