Modes of Biomineralization of Magnetite by Microbes

Biomineralization processes have traditionally been grouped into two distinct modes; biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). In BIM, microbes cause mineral formation by sorbing solutes onto their cell surfaces or extruded organic polymers and/or releasing reactive metabolites which alter the saturation state of the solution proximal to the cell or polymer surface. Such mineral products appear to have no specific recognized functions. On the other hand, in BCM microbes exert a great degree of chemical and genetic control over the nucleation and growth of mineral particles, presumably because the biominerals produced serve some physiological function. Interestingly, there are examples where the same biomineral is produced by both modes in the same sedimentary environment. For example, the magnetic mineral magnetite (Fe ₃ O ₄ ) is generated extracellularly in the bulk pore waters of sediments by various Fe(III)-reducing bacteria under anaerobic conditions, while some other anaerobic and microaerophilic bacteria and possibly protists form magnetite intracellularly within preformed vesicles. Differences in precipitation mechanisms might be caused by enzymatic activity at specific sites on the surface of the cell. Whereas one type of microbe might facilitate the transport of dissolved Fe(III) into the cell, another type will express its reductive enzymes and cause the reduction of Fe(III) external to the cell. Still other microbes might induce magnetite formation indirectly through the oxidation of Fe(II), followed by the reaction of dissolved Fe(II) with hydrolyzed Fe(III). The biomineralization of magnetite has significant effect on environmental iron cycling, the magnetization of sediments and thus the geologic record, and on the use of biomarkers as microbial fossils.     

Precipitation of iron,silica, and sulfate on bacterial cell surfaces

The present study documents the precipitation of Fe(III), silica, and sulfate in the presence of 3 different bacteria (Bacillus subtilus, Bacillus licheniformis, and Pseudomonas aeruginosa), under different total Fe(III) concentrations (10^?2 M, 10^?3 M, 10^?4 M) at constant pH (4.0). Morphology and chemical composition of the precipitates were compared with those formed in abiotic control systems, while chemical composition and precipitation of the precipitates were modeled according to solution chemistry data. Transmission electron microscopy (TEM) observations showed morphological differences between the biotic and abiotic systems. All systems contained small grains (diam. 2–50 nm), but amorphous material (i.e., material without any specific morphology) and nodules were present only in the cell systems. This is because bacterial surfaces and exopolymers provided numerous binding sites for metal and anion sorption and promoted heterogeneous nucleation of hydrous ferric oxides (HFO). The initial Fe/Si and Fe/SO₄ molar ratios of the solutions dictated the type of precipitates in most systems, since abiotic control systems were saturated to oversaturated with respect to amorphous silica, siliceous ferrihydrite, schwertmannite, ferrihydrite, goethite, or combinations of these. Of the three strains studied, B. licheniformis appeared to have the greatest influence on the chemical composition of the precipitates, especially in the presence of Si. B. licheniformis (a gram‐positive bacterium with a large capsule) favored the precipitation of HFO containing less Si than the predicted solids, because Si rather than Fe oxides was preferentially sorted to extracellular polymers (capsule). On the other hand, the formation of SO₄‐rich HFO (similar to schwertmannite) did not seem to be affected by the presence of bacteria.     

The binding of precipitant ions in the tetragonal crystals of hen egg white lysozyme

Abstract

The bonds between lysozyme molecules and precipitant ions in single crystals grown with chlorides of several metals are analysed on the basis of crystal structure data. Crystals of tetragonal hen egg lysozyme (HEWL) were grown with chlorides of several alkali and transition metals (LiCl, NaCl, KCl, NiCl₂ and CuCl₂) as precipitants and the three-dimensional structures were determined at 1.35?Å resolution by X-ray diffraction method. The positions of metal and chloride ions attached to the protein were located, divided into three groups and analysed. Some of them, in accordance with the recently proposed and experimentally confirmed crystal growth model, provide connections in protein dimers and octamers that are precursor clusters in the crystallization lysozyme solution. The first group, including Cu⁺², Ni⁺² and Na⁺¹ cations, binds specifically to the protein molecule. The second group consists of metal and chloride ions bound inside the dimers and octamers. The third group of ions can participate in connections between the octamers that are suggested as building units during the crystal growth. The arrangement of chloride and metal ions associated with lysozyme molecule at all stages of the crystallization solution formation and crystal growth is discussed.

Communicated by Ramaswamy H. Sarma     

Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 µm thick yttrium iron garnet films that are  > 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.     

重金属污染土壤植物修复中的微生物功能研究进展

综述了国内外在重金属污染土壤植物-微生物联合修复领域的研究报道,总结了近5年的研究实例。植物-微生物联合修复体系具有生物固定与生物去除土壤重金属的两种功能,根际微生物可以菌根、内生菌等方式与根系形成联合体,通过增强植物抗性和优化根际环境,促进根系发展,增强植物吸收和向上转运重金属的能力。建立植物-微生物联合修复体系,可充分发挥植物与微生物作用功能的优势,提高污染土壤的修复效率。增强植物修复体系中微生物功能的重点是深入研究根际微生物、根系和介质载体三者之间复合功能,结合污染土壤类型与植物群落配置的特点筛选扩繁高效菌种与菌群。     

Using euhalophytes to understand salt tolerance and to develop saline agriculture: Suaeda salsa as a promising model

Background As important components in saline agriculture, halophytes can help to provide food for a growing world population. In addition to being potential crops in their own right, halophytes are also potential sources of salt-resistance genes that might help plant breeders and molecular biologists increase the salt tolerance of conventional crop plants. One especially promising halophyte is Suaeda salsa, a euhalophytic herb that occurs both on inland saline soils and in the intertidal zone. The species produces dimorphic seeds: black seeds are sensitive to salinity and remain dormant in light under high salt concentrations, while brown seeds can germinate under high salinity (e.g. 600 mm NaCl) regardless of light. Consequently, the species is useful for studying the mechanisms by which dimorphic seeds are adapted to saline environments. S. salsa has succulent leaves and is highly salt tolerant (e.g. its optimal NaCl concentration for growth is 200 mm). A series of S. salsa genes related to salt tolerance have been cloned and their functions tested: these include SsNHX1, SsHKT1, SsAPX, SsCAT1, SsP5CS and SsBADH. The species is economically important because its fresh branches have high value as a vegetable, and its seed oil is edible and rich in unsaturated fatty acids. Because it can remove salts and heavy metals from saline soils, S. salsa can also be used in the restoration of salinized or contaminated saline land.Scope Because of its economic and ecological value in saline agriculture, S. salsa is one of the most important halophytes in China. In this review, the value of S. salsa as a source of food, medicine and forage is discussed. Its uses in the restoration of salinized or contaminated land and as a source of salt-resistance genes are also considered.     

镉胁迫对秋华柳根系活力及其Ca、Mg、Mn、Zn、Fe积累的影响

以秋华柳为试验材料,采用水培试验方式,设置CK(0 mg·L^-1 Cd²⁺)、T₁(2 mg·L^-1 Cd²⁺)、T₂(10 mg·L^-1Cd²⁺)、T₃(20 mg·L^-1Cd²⁺)、T₄(50 mg·L^-1Cd²⁺)5种镉处理浓度,通过对秋华柳根系活力,叶、韧皮部、木质部和根部的镉含量,以及Ca、Mg、Mn、Zn、Fe 5种常规金属元素含量的测定,研究了不同浓度镉胁迫下秋华柳根系活力及Ca、Mg、Mn、Zn、Fe 等金属元素含量的变化.结果表明:1)秋华柳根系活力随着镉处理浓度的增加而逐渐下降,当镉浓度≥10 mg·L^-1时,根系活力与对照相比显著下降.2)随着镉处理浓度的增加,秋华柳叶中Fe的积累受到显著抑制;韧皮部Mg、Mn、Fe的积累受到显著抑制;木质部Ca、Mg、Mn、Zn、Fe 等5种常规金属元素的积累无显著性差异;根部5种常规金属元素的吸收和积累受到显著抑制,表现出镉对其他金属元素积累的拮抗作用.其中,50 mg·L^-1的镉胁迫下,根部Zn的积累量降幅最大,受Cd的抑制最明显.3)各处理组Fe的转移系数与对照相比均无显著性差异;Ca、Mg、Mn、Zn的转移系数均高于对照,且在一定的镉处理水平上差异显著.4)镉胁迫下,秋华柳根部镉的积累量与Ca的积累量呈显著负相关,与其他4种常规金属元素的积累量呈极显著负相关,说明根部常规金属元素的变化可作为秋华柳受镉毒害程度的指示之一.     

Radially Oriented Single‐Crystal Primary Nanosheets Enable Ultrahigh Rate and Cycling Properties of LiNi0.8Co0.1Mn0.1O2 Cathode Material for Lithium‐Ion Batteries

Ni‐rich Li[Ni_xCo_yMn_1?x?y]O₂ (x ≥ 0.8) layered oxides are the most promising cathode materials for lithium‐ion batteries due to their high reversible capacity of over 200 mAh g^?1. Unfortunately, the anisotropic properties associated with the α‐NaFeO₂ structured crystal grains result in poor rate capability and insufficient cycle life. To address these issues, a micrometer‐sized Ni‐rich LiNi_0.8Co_0.1Mn_0.1O₂ secondary cathode material consisting of radially aligned single‐crystal primary particles is proposed and synthesized. Concomitant with this unique crystallographic texture, all the exposed surfaces are active {010} facets, and 3D Li⁺ ion diffusion channels penetrate straightforwardly from surface to center, remarkably improving the Li⁺ diffusion coefficient. Moreover, coordinated charge–discharge volume change upon cycling is achieved by the consistent crystal orientation, significantly alleviating the volume‐change‐induced intergrain stress. Accordingly, this material delivers superior reversible capacity (203.4 mAh g^?1 at 3.0–4.3 V) and rate capability (152.7 mAh g^?1 at a current density of 1000 mA g^?1). Further, this structure demonstrates excellent cycling stability without any degradation after 300 cycles. The anisotropic morphology modulation provides a simple, efficient, and scalable way to boost the performance and applicability of Ni‐rich layered oxide cathode materials.     

Contamination on sandflats and the decoupling of linked ecological functions

Benthic macrofauna can influence inputs and transformations of energy and matter in estuaries, affecting both the stocks of vital materials (e.g. carbon, oxygen) and the rates of key processes (e.g. organic matter decomposition, nutrient uptake). Although a number of studies have identified shifts in functional groups or biological traits in relation to anthropogenic stressors, there have been few field‐based assessments of changes in functioning associated with stress gradients. We used a comparative experimental approach to investigate functioning on two sandflats with differing exposures to urban contaminants. Apart from significant differences in sediment contaminant concentrations (43.2 ± 1.8 mg kg^?1 Zn and 15.6 ± 0.9 mg kg^?1 Pb at the Pollen site; 17.7 ± 0.7 mg kg^?1 Zn and 7.9 ± 0.9 mg kg^?1 Pb at the Waiheke site), the two sandflats were readily comparable: both had similar sediment grain size distributions and were dominated by the same macrofaunal species; and both were in non‐eutrophic New Zealand marine reserves with low ambient sediment organic matter content. To better understand the effects of contaminants on biologically mediated transformations of organic matter into inorganic nutrients, we manipulated sediment organic matter content and macrofaunal abundance in standardized treatments at each site. Fluxes of oxygen and ammonium, which are linked to key sandflat processes such as organic matter decomposition and benthic photosynthesis, were measured as response variables 1 week after the experimental manipulations. We predicted more efficient organic matter processing on the uncontaminated flat and thus expected to see elevated ammonium efflux in response to organic enrichment treatments at this site. Higher rates of benthic photosynthesis were predicted for plots with higher ammonium efflux, as ammonium is a readily utilizable form of limiting inorganic nitrogen. We documented significant positive relationships between ammonium uptake and benthic primary production on the uncontaminated flat, but weaker/insignificant relationships at the contaminated site. Our data were consistent with theories of increased variability and a decoupling of system processes with increasing amounts of stress.     

Development of Next‐Generation Organic‐Based Solar Cells: Studies on Dye‐Sensitized and Perovskite Solar Cells

Next‐generation organic solar cells such as dye‐sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are studied at the National Institute of Advanced Industrial Science and Technology (AIST), and their materials, electronic properties, and fabrication processes are investigated. To enhance the performance of DSSCs, the basic structure of an electron donor, π‐electron linker, and electron acceptor, i.e., D–π–A, is suggested. In addition, special organic dyes containing coumarin, carbazole, and triphenylamine electron donor groups are synthesized to find an effective dye structure that avoids charge recombination at electrode surfaces. Meanwhile, PSCs are manufactured using both a coating method and a laser deposition technique. The results of interfacial studies demonstrate that the level of the conduction band edge (CBE) of a compact TiO₂ layer is shifted after TiCl₄ treatment, which strongly affects the solar cell performance. Furthermore, a special laser deposition system is developed for the fabrication of the perovskite layers of PSCs, which facilitates the control over the deposition rate of methyl ammonium iodide used as their precursor.