Phytoremediation of heavy metals: A green technology

The environment has been contaminated with organic and inorganic pollutants. Organic pollutants are largely anthropogenic and are introduced to the environment in many ways. Soil contamination with toxic metals, such as Cd, Pb, Cr, Zn, Ni and Cu, as a result of worldwide industrialization has increased noticeably within the past few years. There are some conventional remediation technologies to clean polluted areas, specifically soils contaminated with metals. In spite of being efficient, these methods are expensive, time consuming, and environmentally devastating. Recently, phytoremediation as a cost effective and environmentally friendly technology has been developed by scientists and engineers in which biomass/microorganisms or live plants are used to remediate the polluted areas. It can be categorized into various applications, including phytofiltration, phytostabilization, phytoextraction, and phytodegradation. A brief review of phytoremediation of soils contaminated with heavy metals has been complied to provide an extensive applicability of this green technology.Key words: Phytoremediation, heavy metals, soil pollution, toxicity

Relevance of Lysine Snorkeling in the Outer Transmembrane Domain of Small Viral Potassium Ion Channels

Transmembrane domains (TMDs) are often flanked by Lys or Arg because they keep their aliphatic parts in the bilayer and their charged groups in the polar interface. Here we examine the relevance of this so-called “snorkeling” of a cationic amino acid, which is conserved in the outer TMD of small viral K+ channels. Experimentally, snorkeling activity is not mandatory for KcvPBCV-1 because K29 can be replaced by most of the natural amino acids without any corruption of function. Two similar channels, KcvATCV-1 and KcvMT325, lack a cytosolic N-terminus, and neutralization of their equivalent cationic amino acids inhibits their function. To understand the variable importance of the cationic amino acids, we reanalyzed molecular dynamics simulations of KcvPBCV-1 and N-terminally truncated mutants; the truncated mutants mimic KcvATCV-1 and KcvMT325. Structures were analyzed with respect to membrane positioning in relation to the orientation of K29. The results indicate that the architecture of the protein (including the selectivity filter) is only weakly dependent on TMD length and protonation of K29. The penetration depth of Lys in a given protonation state is independent of the TMD architecture, which leads to a distortion of shorter proteins. The data imply that snorkeling can be important for K+ channels; however, its significance depends on the architecture of the entire TMD. The observation that the most severe N-terminal truncation causes the outer TMD to move toward the cytosolic side suggests that snorkeling becomes more relevant if TMDs are not stabilized in the membrane by other domains

Relevance of Lysine Snorkeling in the Outer Transmembrane Domain of Small Viral Potassium Ion Channels

Transmembrane domains (TMDs) are often flanked by Lys or Arg because they keep their aliphatic parts in the bilayer and their charged groups in the polar interface. Here we examine the relevance of this so-called “snorkeling” of a cationic amino acid, which is conserved in the outer TMD of small viral K+ channels. Experimentally, snorkeling activity is not mandatory for KcvPBCV-1 because K29 can be replaced by most of the natural amino acids without any corruption of function. Two similar channels, KcvATCV-1 and KcvMT325, lack a cytosolic N-terminus, and neutralization of their equivalent cationic amino acids inhibits their function. To understand the variable importance of the cationic amino acids, we reanalyzed molecular dynamics simulations of KcvPBCV-1 and N-terminally truncated mutants; the truncated mutants mimic KcvATCV-1 and KcvMT325. Structures were analyzed with respect to membrane positioning in relation to the orientation of K29. The results indicate that the architecture of the protein (including the selectivity filter) is only weakly dependent on TMD length and protonation of K29. The penetration depth of Lys in a given protonation state is independent of the TMD architecture, which leads to a distortion of shorter proteins. The data imply that snorkeling can be important for K+ channels; however, its significance depends on the architecture of the entire TMD. The observation that the most severe N-terminal truncation causes the outer TMD to move toward the cytosolic side suggests that snorkeling becomes more relevant if TMDs are not stabilized in the membrane by other domains

Phycodnavirus Potassium Ion Channel Proteins Question the Virus Molecular Piracy Hypothesis

Phycodnaviruses are large dsDNA, algal-infecting viruses that encode many genes with homologs in prokaryotes and eukaryotes. Among the viral gene products are the smallest proteins known to form functional K+ channels. To determine if these viral K+ channels are the product of molecular piracy from their hosts, we compared the sequences of the K+ channel pore modules from seven phycodnaviruses to the K+ channels from Chlorella variabilis and Ectocarpus siliculosus, whose genomes have recently been sequenced. C. variabilis is the host for two of the viruses PBCV-1 and NY-2A and E. siliculosus is the host for the virus EsV-1. Systematic phylogenetic analyses consistently indicate that the viral K+ channels are not related to any lineage of the host channel homologs and that they are more closely related to each other than to their host homologs. A consensus sequence of the viral channels resembles a protein of unknown function from a proteobacterium. However, the bacterial protein lacks the consensus motif of all K+ channels and it does not form a functional channel in yeast, suggesting that the viral channels did not come from a proteobacterium. Collectively, our results indicate that the viruses did not acquire their K+ channel-encoding genes from their current algal hosts by gene transfer; thus alternative explanations are required. One possibility is that the viral genes arose from ancient organisms, which served as their hosts before the viruses developed their current host specificity. Alternatively the viral proteins could be the origin of K+ channels in algae and perhaps even all cellular organisms

Analysis of polysilicon micro beams buckling with temperature-dependent properties

The suspended electrothermal polysilicon micro beams generate displacements and forces by thermal buckling effects. In the previous electro-thermal and thermo-elastic models of suspended polysilicon micro beams, the thermo-mechanical properties of polysilicon have been considered constant over a wide rang of temperature (20-900°C). In reality, the thermo-mechanical properties of polysilicon depend on temperature and change significantly at high temperatures. This paper describes the development and validation of theoretical and Finite Element Model (FEM) including the temperature dependencies of polysilicon properties such as thermal expansion coefficient and Young\u92s modulus. In the theoretical models, two parts of elastic deflection model and thermal elastic model of micro beams buckling have been established and simulated. Also, temperature dependent buckling of polysilicon micro beam under high temperature has been modeled by Finite Element Analysis (FEA). Analytical results and numerical results using FEA are compared with experimental data available in literature. Their reasonable agreement validates analytical model and FEM. This validation indicates the importance of including temperature dependencies of polysilicon thermo-mechanical properties such as Coefficient of Thermal Expansion (CTE) in the previous models

Synthesis and Surface Characterization of Magnetite-Titania Nanoparticles/Polyamide Nanocomposite Smart RO Membrane

AbstractIn the water desalination technology, utilizing nanocomposite membranes have been an interesting approach to improve the water permeability and rejection properties of conventional reverse osmosis (RO) membranes. In this research, effects of magnetite (Fe3O4) and titania (TiO2) nanoparticles by loading in trimesoyl chloride (TMC) organic solution and in metaphenylene diamine (MPD) aqueous solutions on the surface characteristics of polyamide layer have been investigated. Also, the morphology and EDS line and map analysis of Fe3O4 coated PSf layer and in-situ reduced Fe3O4 by impregnation of precursors inside PSf layer after formation of PA top coat, have been considered. The morphology, dispersion of nanoparticles, surface bonds of magnetite and titania nanoparticles with polyamide and hydrophilicity of magnetic nanocomposite RO membrane has been taken into account in each method by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and contact angle measurement. Trace of nanoparticles inside membrane cross section has been analyzed by energy dispersive spectroscopy (EDS) method. The samples were implemented to the different magnetite nanoparticle weight percent caused to the variation of surface energy, contact angle, roughness and polyamide layer free bonds. In addition the optimum concentration of magnetite nanoparticles for improvement in surface properties of high efficiency reverse osmosis membrane was obtained. The results can provide a versatile technique for fabrication of high efficiency magnetic responsive nanocomposite smart RO membranes

Environmental impact of rice production based on nitrogen fertilizer use

While essential to food production, nitrogen (N) fertilizers in agricultural ecosystems are also important sources of environmental pollution nationally and globally. The environmental impact of three N fertilization levels (30, 60, and 90\ua0kg\ua0ha-1) plus a non-N control (0\ua0kg\ua0ha-1) in growing three rice cultivars (cv. Hashemi, cv. Alikazemi, and cv. Khazar) were assessed for 2\ua0years in northern Iran, with the methodology of the life cycle assessment (LCA). The impact categories evaluated in this study were global warming, acidification, terrestrial eutrophication, and depletion of fossil, phosphate, and potassium resources. Over cultivars, no use of N fertilizer provided the lowest grain yield (2194\ua0kg\ua0ha-1), whereas the N rates of 60 and 90\ua0kg\ua0ha-1increased grain yield by 52.9 and 66.9%, respectively. Over N rates, cv. Khazar produced the highest grain yield (3415\ua0kg\ua0ha-1) and cv. Hashemi the lowest (2663\ua0kg\ua0ha-1). On-farm (foreground) emissions were higher than off-farm (background) emissions in most impact categories. The maximum value of environmental index (1.33) was observed for cv. Hashemi with 90\ua0kg\ua0N\ua0ha-1, while the minimum value (0.38) was observed for cv. Khazar without N fertilization. Moreover, cv. Khazar showed the lowest resource depletion index (0.44) with 90\ua0kg\ua0N\ua0ha-1, whereas cv. Hashemi with no use of N showed the maximum value (0.96). Over cultivars, high N rates imposed drastic impact to the categories acidification and terrestrial eutrophication. However, selection of high-yielding cultivars significantly alleviated the impact to most categories. Fertilization that enables optimal yields, in accordance with the nutrient requirements of crops, ensures the most efficient land use and sustainable rice production