Photocatalytic redox-neutral α-C(sp3)-H pyridination of glycine derivatives and N-arylamines with cyanopyridines.

A photo-induced α-C(sp3)-H decyanative pyridination of N-arylglycine derivatives with cyanopyridines was developed. This reaction was performed under organic photocatalytic and redox-neutral conditions via a radical-radical cross-coupling process. Besides, the protocol was also suitable for the C(sp3)-H pyridination of N-aryl tetrahydroisoquinolines as well as benzylamines.

Influence of citrate/tartrate on chromite crystallization behavior and its potential environmental implications.

The ferrite process has been developed to purify wastewater containing heavy metal ions and recycle valuable metals by forming chromium ferrite. However, organic matter has an important influence on the crystallization behavior and stability of chromite synthesized from chromium-containing wastewater. We focused on the influence and effect mechanism of two typical organic acid salts (citrate (CA) and tartrate (TA)) on the process of chromium mineralization. It was found that the presence of organic matter leads to the increase of the residual content of Cr in CA system (0.50 mmol/L) and TA system (0.61 mmol/L) in the solution, and the removal of chromium was mainly due to the surface adsorption of Fe(III) hydrolysate. The decreased crystallinity of mineralized products is ascribed to the completion of organic compounds with Fe(II) and Fe(III), which hinders the formation of ferrite precursors. There was bidentate and monodentate chelation between -COO- and metal ions in the CA system and TA system respectively, which resulted in a stronger affinity between CA and iron. This study provides the underlying mechanism for Cr(III) solid oxidation by the ferrite method in an organic matter environment and is of great significance to prevent and control chromium pollution in the environment.

Resource recovery: Adsorption and biomineralization of cerium by Bacillus licheniformis.

Cerium is a critical element to modern technologies. Nowadays, its increased applications have led to elevated levels in the environment. Cerium recovery by microorganisms has gained a great deal of attention. Here, our research showed that Bacillus licheniformis could be used to recover Ce3+ from aqueous solution. The adsorption capacity of cerium on this bacterial strain achieved 38.93 mg/g (dry weight) biomass. Adsorption kinetics followed a pseudo-second-order rate model, and adsorption isotherm was fitted well with the Freundlich model. Scanning electron microscope (SEM) observations coupled with X-ray energy dispersive spectroscopy (EDS) analysis revealed a spatial association of Ce with C, N, O, S, and P. Fourier transform infrared spectroscopy (FT-IR) analysis further suggested that the phosphate and carboxyl groups on the cell surface might be responsible for the adsorption of cerium. Furthermore, X-ray diffraction (XRD) and transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) suggested that cerium initially occurred on the bacterial cell surface as Ce(OH)3, which was mainly converted to monazite (CePO4) and a small amount of CeO2 overtime. Hydrothermal treatment was used to accelerate the mineralization process of cerium by B. licheniformis. The hydrothermal treatment is conducted for comparative analysis of mineralization process in extreme geological condition.

Adsorption and mineralization of REE-lanthanum onto bacterial cell surface.

A large number of rare earth element mining and application resulted in a series of problems of soil and water pollution. Environmental remediation of these REE-contaminated sites has become a top priority. This paper explores the use of Bacillus licheniformis to adsorb lanthanum and subsequent mineralization process in contaminated water. The maximum adsorption capacity of lanthanum on bacteria was 113.98 mg/g (dry weight) biomass. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data indicated that adsorbed lanthanum on bacterial cell surface occurred in an amorphous form at the initial stage. Scanning electron microscopy with X-ray energy-dispersive spectroscopy (SEM/EDS) results indicated that lanthanum adsorption was correlated with phosphate. The amorphous material was converted into scorpion-like monazite (LaPO4 nanoparticles) in a month. The above results provide a method of using bacterial surface as adsorption and nucleation sites to treat REE-contaminated water.

Bio-remediation of acephate-Pb(II) compound contaminants by Bacillus subtilis FZUL-33.

Removal of Pb(2+) and biodegradation of organophosphorus have been both widely investigated respectively. However, bio-remediation of both Pb(2+) and organophosphorus still remains largely unexplored. Bacillus subtilis FZUL-33, which was isolated from the sediment of a lake, possesses the capability for both biomineralization of Pb(2+) and biodegradation of acephate. In the present study, both Pb(2+) and acephate were simultaneously removed via biodegradation and biomineralization in aqueous solutions. Batch experiments were conducted to study the influence of pH, interaction time and Pb(2+) concentration on the process of removal of Pb(2+). At the temperature of 25°C, the maximum removal of Pb(2+) by B.subtilis FZUL-33 was 381.31±11.46mg/g under the conditions of pH5.5, initial Pb(2+) concentration of 1300mg/L, and contact time of 10min. Batch experiments were conducted to study the influence of acephate on removal of Pb(2+) and the influence of Pb(2+) on biodegradation of acephate by B.subtilis FZUL-33. In the mixed system of acephate-Pb(2+), the results show that biodegradation of acephate by B.subtilis FZUL-33 released PO4(3+), which promotes mineralization of Pb(2+). The process of biodegradation of acephate was affected slightly when the concentration of Pb(2+) was below 100mg/L. Based on the results, it can be inferred that the B.subtilis FZUL-33 plays a significant role in bio-remediation of organophosphorus-heavy metal compound contamination.

The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains.

The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains was investigated in the present work. Our data showed that the bacteria isolated from uranium mine possessed highly accumulation ability to U(VI), and the maximum accumulation capacity was around 400 mg U/g biomass (dry weight). X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) analyzes indicated that the U(VI) was adsorbed on the bacterial surface firstly through coordinating with phosphate, CH2 and amide groups, and then needle-like amorphous uranium compounds were formed. With the extension of time, the extracellular crystalline substances were disappeared, but some particles were appeared in the intracellular region, and these particles were characterized as tetragonal-uramphite. Moreover, the disrupted experiment indicated that the cell-free extracts had better uranium-immobilization ability than cell debris. Our findings provided the understanding of the uranium transformation process from amorphous uranium to crystalline uramphite, which would be useful in the regulation of uranium immobilization process.

Investigation of Cr(VI) reduction and Cr(III) immobilization mechanism by planktonic cells and biofilms of Bacillus subtilis ATCC-6633.

In this study, we investigated the Cr(VI) uptake mechanism of planktonic cells and biofilms of Bacillus subtilis (B. subtilis) ATCC-6633. Data showed that the effect of planktonic cells on the Cr(VI) uptake was quite different from that of biofilms. Planktonic cells had strong ability of Cr(VI) reduction, while biofilms possessed a great potential of Cr(III) immobilization. For planktonic cells, 100 mg/L Cr(VI) could be completely reduced. Both exopolymeric substances and cytoplasmic extracts contributed to high capacity of Cr(VI) reduction. After the reduction, noticeable Cr(III) precipitates were accumulated on bacterial surfaces, but 37.5% Cr(III) still remained in the supernatant. For biofilms, the biofilm debris became the main active ingredient of the Cr(VI) reduction. However, only 20 mg/L Cr(VI) could be reduced probably because of unavailability of reducing active sites during the biofilm formation. Further studies showed that biofilms had a better Cr(III) immobilization capacity than planktonic cells with 100% Cr(III) immobilized. Moreover, for the first time, we proposed a strategy combining the advantages of both planktonic cells and biofilms, and a successful Cr(VI) removal from typical Cr(VI)-containing plating wastewater was achieved through a 10-L pilot-scale experiment.

Investigation of antibacterial activity and related mechanism of a series of nano-Mg(OH)2.

Here we reported the antibacterial effect and related mechanism of three nano-Mg(OH)(2) slurries using Escherichia coli as model bacteria. X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analysis revealed that the as-synthesized Mg(OH)(2)_(MgCl2), Mg(OH)(2)_(MgSO4) and Mg(OH)(2)_(MgO) are all composed by nanoflakes with different sizes, and their aggregates in water are 5.5, 4.5, and 1.2 µm, respectively. Bactericidal tests showed that the antibacterial efficiency is conversely correlated with the size of Mg(OH)(2) aggregates. Transmission electron microscopy (TEM) observation have not provided evidence of cellular internalization, however, the antibacterial effect is positive correlation to the loss of integrity of cell walls. SEM and zeta potential analysis revealed that the adhering ability of Mg(OH)(2) on the bacterial surface is Mg(OH)(2)_(MgCl2) > Mg(OH)(2)_(MgSO4) > Mg(OH)(2)_(MgO), indicating the toxicity of Mg(OH)(2) may be caused by the electrostatic interaction-induced external adsorption. Confocal laser scanning microscopy (CLSM) further revealed that the adhering of Mg(OH)(2) on the bacterial surface could increase the permeability of cell membranes. Taken together, the antibacterial mechanism of nano-Mg(OH)(2) could be as follows: nano-Mg(OH)(2) adsorbed on the bacterial surface by charge attraction first, and then destroyed the integrity of cell walls, which resulting in the final death of bacteria.

Cr(VI) uptake mechanism of Bacillus cereus.

In this study, we investigated the Cr(VI) uptake mechanism in an indigenous Cr(VI)-tolerant bacterial strain -Bacillus cereus through batch and microscopic experiments. We found that both the cells and the supernatant collected from B. cereus cultivation could reduce Cr(VI). The valence state analysis revealed the complete transformation from Cr(VI) into Cr(III) by living B. cereus. Further X-ray absorption fine structure and Fourier transform infrared analyses showed that the reduced Cr(III) was coordinated with carboxyl and amido functional groups from either the cells or supernatant. Scanning electron microscopy and atomic force microscopy observation showed that noticeable Cr(III) precipitates were accumulated on bacterial surfaces. However, Cr(III) could also be detected in bacterial inner portions by using transmission electron microscopy thin section analysis coupled with energy dispersive X-ray spectroscopy. Through quantitative analysis of chromium distribution, we determined the binding ratio of Cr(III) in supernatant, cell debris and cytoplasm as 22%, 54% and 24%, respectively. Finally, we further discussed the role of bacterium-origin soluble organic molecules to the remediation of Cr(VI) pollutants.

The analysis of the immobilization mechanism of Ni(II) on Bacillus cereus.

This work focused on the identification of biosorption mechanism of Ni(II) by living Bacillus cereus (B. cereus) based on batch experiments and a variety of microscopic equipments. The adsorption equilibrium reached rapidly in 2 h and the maximum nickel adsorption capability of B. cereus was 17.7 mg x g(-1) (dry weight). Atomic force microscopy (AFM) analysis showed that the bacterial surface roughness increased from 7.9 +/- 0.5 nm to 12.6 +/- 1.6 nm during this process. Scanning electron microscopy (SEM) observation confirmed that there was Ni(II) on the bacterial surface. However, transmission electron microscopy (TEM) thin section analysis coupled with energy dispersive X-ray spectroscopy (EDS) revealed that Ni(II) could also be found in the inner portions of the bacteria. Inductive coupled plasma emission spectrometer (ICP-OES) quantitative analysis elucidated that over 70% of the immobilized Ni(II) was binding on the surface of bacteria. X-ray diffraction (XRD) analysis showed that the Ni(II) collected by the bacteria was amorphous. Fourier transform infrared (FT-IR) analysis indicated that amides and carboxylation functional groups might be involved in the coordination of Ni(II).

Bioremediation of Cr(VI) and immobilization as Cr(III) by Ochrobactrum anthropi.

Bioremediation of Cr(VI) through reduction relies on the notion that the produced Cr(III) may be precipitated or efficiently immobilized. However, recent reports suggest that soluble organo-Cr(III) complexes are present in various chromate-reducing bacterial systems. This work was designed to explore the factors that affect the immobilization of Cr(III) in the Ochrobactrum anthropi system. X-ray absorption fine structure analysis on the cell debris clearly verified that coordination of Cr(III) occurs on the surfaces via the chelating coordination with carboxyl- and amido-functional groups. However, competitive coordination experiments of Cr(III) revealed that the small molecules such as amino acids and their derivatives or multicarboxyl compounds hold stronger coordination ability with Cr(III) than with cell debris. We speculate that it is the preferential coordination of Cr(III) to the soluble organic molecules in the bacterial culture medium that inhibits effective immobilization of Cr(III) on the cells. On the basis of this understanding, a strategy with two-step control of the medium was proposed, and this achieved successful immobilization of Cr(VI) as Cr(III) by O. anthropi and Planococcus citreus in 5-50 L pilot-scale experiments.

Identification and characterization of the chromium (VI) responding protein from a newly isolated Ochrobactrum anthropi CTS-325.

A Gram-negative, chromium(VI) tolerant and reductive strain CTS-325, isolated from a Chinese chromate plant, was identified as Ochrobactrum anthropi based on its biochemical properties and 16S rDNA sequence analysis. It was able to tolerate up to 10 mmol/L Cr(VI) and completely reduce 1 mmol/L Cr(VI) to Cr(III) within 48 h. When the strain CTS-325 was induced with Cr(VI), a protein increased significantly in the whole cell proteins. Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis revealed that this protein was a superoxide dismutase (SOD) homology. The measured superoxide dismutase activity was 2694 U/mg after three steps of purification. The SOD catalyzes the dismutation of the superoxide anion (O2*-) into hydrogen peroxide and molecular oxygen. This protein is considered to be one of the most important anti-oxidative enzymes for O. anthropi as it allows the bacterium to survive high oxygen stress environments, such as the environment produced during the reduction process of Cr(VI).

Microscopic investigations of the Cr(VI) uptake mechanism of living Ochrobactrum anthropi.

A basic understanding related to the immobilization of chromium by bacteria is essential for chromate pollutant remediation in the environment. In this work, we studied the Cr(VI) uptake mechanism of living Ochrobactrum anthropi and the influence of a bacterial culture medium on the Cr-immobilization process. It was found that the Cr-immobilization ratio of bacteria in Tris-HCl buffer is higher than in LB medium. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis revealed that the chromium accumulated on bacteria were mostly in Cr(III) states. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations showed that noticeable Cr(III) precipitates were accumulated on bacterial surfaces. AFM roughness analysis revealed that the surface roughness of bacteria increased greatly when the bacteria-Cr(VI) interaction was in Tris-HCl buffer rather than in LB solution. Transmission electron microscopy (TEM) thin section analysis coupled with energy-dispersive X-ray spectroscopy showed that Cr(III) is also distributed in bacterial inner portions. A chromium-immobilization mechanism considering the participation of both bacterial inner portions and bacterial surfaces of living Ochrobactrum anthropi was proposed, whereas the bacterial surface was the dominant part of the immobilization of Cr(III). This work also proved that the control of Cr immobilization by living Ochrobactrum anthropi could be achieved via adjusting the bacterial culture medium.

Surface-mediated chromate-resistant mechanism of Enterobacter cloacae bacteria investigated by atomic force microscopy.

The Enterobacter cloacae CYS-25 strain isolated from a chromate plant shows a strong capability for chromate resistance instead of chromate reduction in aerobic conditions. In this study, atomic force microscopy (AFM) was used for studying the morphology characteristics of bacterial properties during the chromate resistance process. The average length of E. cloacae bacteria in the stationary phase is about 2.3 +/- 0.6 microm, while under the stimulation of 400 mg/L CrO42-, the length of bacteria increases to 3.2 +/- 0.7 microm. Height and phase images showed that, with the addition of CrO42-, the smooth surface of bacteria changed into one with discontinuous features with characteristic dimension of 40-200 nm. Analysis reveals that these compact convex patches are organic components stimulated by CrO42-. A chromate resistance mechanism relating to the overexpression of extracellular biologic components for preventing the permeability of CrO42- into the cell is proposed as the survival strategy of E. cloacae in chromate situation.

Preparation of nitrilotriacetic acid/Co2+-linked, silica/boron-coated magnetite nanoparticles for purification of 6 x histidine-tagged proteins.

In this report, we describe the preparation of novel nitrilotriacetic acid/Co2+-linked, silica/boron-coated magnetite nanoparticles for purification of 6 x His-tagged proteins. The nanoparticles were approximately 200 nm in size and were stable against hydrochloric acid and had negligible non-specific binding for protein. Elimination of non-specific binding by nucleic acids was readily achieved by digestion of samples with DNase and RNase. The modified nanoparticles were used to purify two model proteins: one had a C-terminal 6 x His tag, and the other had an internal 6 x His tag. Both proteins were purified within one hour into single band purity on sodium dodecyl sulfate-polyacrylamide electrophoresis gel.

Preparation of His-tagged armored RNA phage particles as a control for real-time reverse transcription-PCR detection of severe acute respiratory syndrome coronavirus.

Armored RNA has been increasingly used as both an external and internal positive control in nucleic acid-based assays for RNA virus. In order to facilitate armored RNA purification, a His6 tag was introduced into the loop region of the MS2 coat protein, which allows the exposure of multiple His tags on the surface during armored RNA assembly. The His-tagged armored RNA particles were purified to homogeneity and verified to be free of DNA contamination in a single run of affinity chromatography. A fragment of severe acute respiratory syndrome coronavirus (SARS-CoV) genome targeted for SARS-CoV detection was chosen for an external positive control preparation. A plant-specific gene sequence was chosen for a universal noncompetitive internal positive control preparation. Both controls were purified by Co2+ affinity chromatography and were included in a real-time reverse transcription-PCR assay for SARS-CoV. The noncompetitive internal positive control can be added to clinical samples before RNA extraction and enables the identification of potential inhibitive effects without interfering with target amplification. The external control could be used for the quantification of viral loads in clinical samples.

[Construction of RNA-containing virus-like nanoparticles expression vector with cysteine residues on surface and fluorescent decoration].

Site-directed mutagenesis was performed at the codon 15 of the MS2 bacteriophage coat protein gene,which had been cloned to the virus-like particles expression vector containing non-self RNA fragment. The produced expression vector,termed pARSC, was transformed to E. coli DH5alpha. The positive clones were selected and proliferated. The harvested cells were treated with sonication and the supernatant was then subjected to linear sucrose density gradients centrifugation (15% to 60%) at 32000 r/min for 4 h at 4 degrees C. The virus-like particles, VLP-Cy, were collected at 35% sucrose density. The particles were examined by transmission electron microscopy and the spherical viral particles of approximately 27 nm in diameter were found. The thiolated VLP-Cy was then chemically modified with fluorescein -5'-maleimide. The covalent fluorescent labeling was confirmed by absorption analysis, SDS-PAGE and MALDI-TOF mass spectroscopy. This is the first report of preparation of RNA-containing natural fluorescent nanoparticles. The study highlight the versatility of MS2 bacteriophage capsids as building blocks for functional nanomaterials construction for a variety of application purposes.