Effectiveness of Vetiver Grass (Vetiveria Zizanioides L. Nash) for Phytoremediation of Endosulfan in Two Cotton Soils from Burkina Faso

The influence of vetiver grass (Vetiveria zizanioides) on the fate of endosulfan was studied using a vertisol and a lixisol soils from cotton-growing areas of Burkina Faso. Endosulfan adsorption isotherms were prepared for planted and unplanted soils. Pot experiments were then conducted for six months. For both soils, endosulfan adsorption was higher on planted soils (K_f= 6.53–9.73 mg^1–nLⁿkg^–1) than on unplanted soils (6.27–7.24 mg^1–nLⁿkg^–1). In unplanted soils, vertisol adsorbed more endosulfan than lixisol. From the pot experiments, the estimated half-lives of endosulfan in unplanted soils (40.6 to 43.1 days) were higher than in planted soils (34.5 to 40.6 days) containing a greater number of endosulfan-degrading microorganisms. Six months after treatment, endosulfan was not detected in soils. The effectiveness of vetiver in promoting adsorption and the disappearance of endosulfan in both studied soils should be validated on the cotton plot scale in Burkina Faso.     

耐镉甲基营养芽胞杆菌吸附条件的优化及其抗逆性

【目的】对所筛选的1株耐镉甲基营养芽胞杆菌NTGB29进行了环境抗逆性的研究,及影响菌株吸附镉离子效率的条件优化。【方法】以发酵液活菌数为指标,研究其对不同NaCl浓度、酸碱度、镉离子浓度的耐受情况;进一步通过单因素实验和响应面法优化影响菌株镉离子吸附效率的发酵条件;以有效镉离子含量为指标,验证菌株在镉污染土壤中的吸附效果。【结果】结果表明,菌株NTGB29对NaCl浓度、酸碱度、Cd~(2+)浓度的最大耐受值分别为10%、pH11.0、50mg/L;菌株在发酵液初始Cd~(2+)浓度10 mg/L、起始pH 6.4、培养温度37°C、NaCl浓度4.2%、装液量50 mL/250 mL、培养时间24 h时,对Cd~(2+)的吸附率达到79.70%;菌株能有效降低镉污染土壤中的有效镉离子含量,吸附率为29.65%。【结论】菌株NTGB29在较高浓度Cd~(2+)浓度、NaCl浓度及强碱环境条件下仍然能够生长,具有良好的环境抗逆性及Cd~(2+)吸附能力,在镉污染土壤调理剂及微生物功能菌剂的研制方面能够提供有价值的菌种资源。     

Correlations between in vitro potency of polyethylene glycol-protein conjugates and their chromatographic behavior

Pegylation is the most widely used and accepted methodology for half-life extension of biopharmaceutical drugs that also improves physicochemical and biological characteristics of proteins considerably. Most of the positive pharmacological effects of pegylated proteins are believed to be related to an increased hydrodynamic volume and molecular size. To explore the size impact of polyethylene glycol (PEG) on in vitro potency, a series of well-defined conjugates of interferon α-2b (IFN) were prepared with PEGs of different lengths and shapes specifically attached to the N-terminal amino group of the protein. Specificity of the attachment was confirmed by peptide mapping and mass spectroscopy. When potency values determined by reporter gene assay were correlated with methods for molecular weight and size characterization, such as size exclusion chromatography and dynamic light scattering, rough parallels were found. Unexpectedly, the retention times on cation exchange chromatography showed much higher correlation with experimentally determined in vitro potency. It appears that in a series of N-terminally pegylated IFNs, their in vitro potency could be predicted from the retention times on the cation exchange chromatography columns, probably because both methods reflect not only the influence of molecular size but also the impact of protein masking exerted by attached PEG moiety.     

Immobilization of Candida rugosa lipase on sporopollenin from Lycopodium clavatum

Sporopollenin is a natural polymer obtained from Lycopodium clavatum, which is highly stable with constant chemical structure and has high resistant capacity to chemical attack. In this study, immobilization of lipase from Candida rugosa (CRL) on sporopollenin by adsorption method is reported for the first time. Besides this, the enzyme adsorption capacity, activity and thermal stability of immobilized enzyme have also been investigated. It has been observed that under the optimum conditions (Spo-E_(0.3)), the specific activity of the immobilized lipase on the sporopollenin by adsorption was 16.3 U/mg protein, which is 0.46 times less than that of the free lipase (35.6 U/mg protein). The pH and temperature of immobilized enzyme were optimized, which were 6.0 and 40 °C respectively. Kinetic parameters V_max and K_m were also determined for the immobilized lipase. It was observed that there is an increase of the K_m value (7.54 mM) and a decrease of the V_max value (145.0 U/mg-protein) comparing with that of the free lipase.     

Variable luminal sarcoplasmic reticulum Ca buffer capacity in smooth muscle cells

Sarcoplasmic reticulum contains the internal Ca²⁺ store in smooth muscle cells and its lumen appears to be a continuum that lacks diffusion barriers. Accordingly, the free luminal Ca²⁺ level is the same all throughout the SR; however, whether the Ca²⁺ buffer capacity is the same in all the SR is unknown. We have estimated indirectly the luminal Ca²⁺ buffer capacity of the SR by comparing the reduction in SR Ca²⁺ levels with the corresponding increase in [Ca²⁺]_i during activation of either IP₃Rs with carbachol or RyRs with caffeine, in smooth muscle cells from guinea pig urinary bladder. We have determined that carbachol-sensitive SR has a 2.4 times larger Ca²⁺ buffer capacity than caffeine-sensitive SR. Rapid inhibition of SERCA pumps with thapsigargin revealed that this pump activity accounts for 80% and 60% of the Ca²⁺ buffer capacities of carbachol- and caffeine-sensitive SR, respectively. Moreover, the Ca²⁺ buffer capacity of carbachol-sensitive SR was similar to caffeine-sensitive SR when SERCA pumps were inhibited. Similar rates of Ca²⁺ replenishments suggest similar levels of SERCA pump activities for either carbachol- or caffeine-sensitive SR. Paired pulses of caffeine, in conditions of low Ca²⁺ influx, indicate the relevance of luminal SR Ca²⁺ buffer capacity in the [Ca²⁺]_i response. To further study the importance of luminal SR Ca²⁺ buffer capacity in the release process we used low levels of heparin to partially inhibit IP₃Rs. This condition revealed carbachol-induced transient increase of luminal SR Ca²⁺ levels provided that SERCA pumps were active. It thus appears that SERCA pump activity keeps the luminal SR Ca²⁺-binding proteins in the high-capacity, low-affinity conformation, particularly for IP₃R-mediated Ca²⁺ release.     

Dynamic economic analysis on invasive species management: Some policy implications of catchability

The problem of controlling invasive species has emerged as a global issue. In response to invasive species threats, governments often propose eradication. This article challenges the eradication view by studying optimal strategies for controlling invasive species in a simple dynamic model. The analysis mainly focuses on deriving policy implications of catchability in a situation where a series of controlling actions incurs operational costs that derive from the fact that catchability depends on the current stock size of invasive species. We analytically demonstrate that the optimal policy changes drastically, depending on the sensitivity of catchability in response to a change in the stock size, as well as on the initial stock. If the sensitivity of catchability is sufficiently high, the constant escapement policy with some interior target level is optimal. In contrast, if the sensitivity of catchability is sufficiently low, there could exist a threshold of the initial stock which differentiates the optimal action between immediate eradication and giving-up without any control. In the intermediate range, immediate eradication, giving-up without any control, or more complex policies may be optimal. Numerical analysis is employed to present economic intuitions and insights in both analytically tractable and intractable cases.     

Enhancement of the activity and enantioselectivity of lipase in organic systems by immobilization onto low-cost support

Lipase from Arthrobacter sp. was immobilized onto low-cost diatomite materials using different protocols for the resolution of 4-hydroxy-3-methyl-2-(2-propenyl)-2-cyclopenten-1-one (HMPC) by asymmetric acylation. The support surface was grafted various functional groups including methacryloxypropyl, vinyl, octyl, dodecyl and γ-(aminopropyl)-glutaraldehyde. These modifications resulted in various mechanisms during the immobilization and thus introduced different characteristics to the prepared lipases. The interfacially adsorbed lipase onto dodecyl-modified support exhibited both higher activity and stability among these immobilized preparations. The modified enzyme-aggregate coating method was performed based on interfacial adsorption in our work, and the characteristics of this immobilized lipase were investigated and compared with those by cross-linking and interfacial adsorption methods. It was shown that the enzyme-aggregate coated lipase yielded the highest activity with a recovered activity of 8.5-fold of the free enzyme, and the highest operational stability with 85% of initial activity remained after 10 recycles. Excellent enantioselectivity (E ≥ 400, with e.e. = 99% of S-HMPC) was obtained for most lipase preparations in our paper (E = 85 for the free enzyme).     

The role of denitrification on arsenite oxidation and arsenic mobility in an anoxic sediment column model with activated alumina

Arsenite (As(III)) is the predominant arsenic (As) species in reducing environments. As(III) is less strongly adsorbed than As(V) at circumneutral pH conditions by common non‐iron metal oxides in sediments such as those of aluminum. Therefore, oxidation of As(III) to As(V) could contribute to an improved immobilization of As and thus help mitigate As contamination in groundwater. Microbial oxidation of As(III) is known to readily under aerobic conditions, however, the dissolved oxygen (O₂) concentration in groundwater may be limited due to the poor solubility of O₂ and its high chemical reactivity with reduced compounds. Nitrate (${\rm NO}_{3}^{{-} } $ ), can be considered as an alternative electron acceptor, which can support oxidation of As(III) to As(V) by denitrifying bacteria. In this study, two up‐flow sediment columns packed with activated alumina (AA) were utilized to demonstrate the role of denitrification on the oxidation of As(III) to As(V) and its contribution to improved As adsorption onto AA. One column was supplied with ${\rm NO}_{3}^{{-} } $ (C1) and its performance was compared with a control column lacking ${\rm NO}_{3}^{{-} } $ (C2). During most of the operation when the pH was in the circumneutral range (days 50–250), the release of arsenic was greater from C2 compared to C1. The effluent As concentrations started increasing on days 60 and 100 in C2 and C1, respectively. Complete breakthrough started on day 200 in C2; whereas in C1, complete breakthrough was never achieved. The effluent and solid phase As speciation was dominated by As(V) in C1, indicating the occurrence of As(III) oxidation due to ${\rm NO}_{3}^{{-} } $ ; whereas in C2, only As(III) was dominant. This study illustrates a bioremediation or natural attenuation process based on anoxic microbial ${\rm NO}_{3}^{{-} } $ ‐dependent oxidation of As(III) to more readily adsorbed As(V) as a means to enhance the immobilization of As on alumina oxide particles in subsurface environments. Biotechnol. Bioeng. 2010;107: 786–794. © 2010 Wiley Periodicals, Inc.     

Different molecular arrangements of the tetrameric annexin 2 modulate the size and dynamics of membrane aggregation

Annexin 2, a member of the annexin family of Ca²⁺-dependent membrane binding proteins is found in monomeric and heterotetrameric forms and has been involved in different membrane related functions. The heterotetrameric annexin 2 is composed of a dimer of S100A10, a member of the S100 family of Ca²⁺ binding proteins and two annexin 2 molecules ((Anx2-S100A10)₂). Different molecular models including tetramers and octamers in which S100A10 is localized in the centre of the complex with the annexin 2 molecules positioned around S100A10 had been proposed. Herein, the organization of the (Anx2-S100A10)₂ complex in conditions in which membranes are able to bridge was studied. We performed Cryo-electron microscopy observations of the tetrameric annexin 2 on the membrane surface, and study the S100A10 accessibility to antibodies by flow “cytometry”. We also studied the kinetics and size evolution of vesicle aggregates by dynamic light scattering. The results show that the protein is able to organize in three different arrangements depending on the presence of Ca²⁺ and pH and that the aggregation is faster in the presence of Ca²⁺ compared with the aggregation in its absence. In one arrangement the S100A10 molecule is exposed to the solvent allowing its interaction with other proteins. The presented results will serve as a molecular basis to explain some of the functions of the tetrameric annexin 2.     

RNA and DNA interactions with zwitterionic and charged lipid membranes — A DSC and QCM-D study

The aim of the present study is to establish under which conditions tRNA associates with phospholipid bilayers, and to explore how this interaction influences the lipid bilayer. For this purpose we have studied the association of tRNA or DNA of different sizes and degrees of base pairing with a set of model membrane systems with varying charge densities, composed of zwitterionic phosphatidylcholines (PC) in mixtures with anionic phosphatidylserine (PS) or cationic dioctadecyl-dimethyl-ammoniumbromide (DODAB), and with fluid or solid acyl-chains (oleoyl, myristoyl and palmitoyl). To prove and quantify the attractive interaction between tRNA and model-lipid membrane we used quartz crystal microbalance with dissipation (QCM-D) monitoring to study the tRNA adsorption to deposit phospholipid bilayers from solutions containing monovalent (Na⁺) or divalent (Ca²⁺) cations. The influence of the adsorbed polynucleic acids on the lipid phase transitions and lipid segregation was studied by means of differential scanning calorimetry (DSC). The basic findings are: i) tRNA adsorbs to zwitterionic liquid-crystalline and gel-phase phospholipid bilayers. The interaction is weak and reversible, and cannot be explained only on the basis of electrostatic attraction. ii) The adsorbed amount of tRNA is higher for liquid-crystalline bilayers compared to gel-phase bilayers, while the presence of divalent cations show no significant effect on the tRNA adsorption. iii) The adsorption of tRNA can lead to segregation in the mixed 1,2-dimyristoyl-sn-glycerol-3-phosphatidylcholine (DMPC)-1,2-dimyristoyl-sn-glycero-3-phosphatidylserine (DMPS) and DMPC-DODAB bilayers, where tRNA is likely excluded from the anionic DMPS-rich domains in the first system, and associated with the cationic DODAB-rich domains in the second system. iv) The addition of shorter polynucleic acids influence the chain melting transition and induce segregation in a mixed DMPC-DMPS system, while larger polynucleic acids do not influence the melting transition in these system. The results in this study on tRNA-phospholipid interactions can have implications for understanding its biological function in, e.g., the cell nuclei, as well as in applications in biotechnology and medicine.