bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-Time NURBS Interpolator with an Optimal Feed for High-Speed Machining
Authors: Feng Jing Chun , Wang Yu Han , Chen Ming , Wang Jin Sen
Published: September 2009

NURBS interpolation has many advantages over the traditional linear or circular interpolation in high-speed machining. The existing work in this regard focuses on adaptive feed interpolation considering the chord error constraints and tangent acceleration limits. However, regardless of the dynamic characteristics of individual axis, performance will inevitably suffer when the system is called upon to execute a complex trajectory beyond the range of its capabilities. The intent of the present work is to provide an optimal feed interpolation method respecting both the chord error constraint and the drive constraint of each axis. A look-ahead scheme is applied with a moving window to augment the calculation efficiency for real-time application. Simulations are performed to verify the resulting feedrate, acc/dec profiles and the real-time performance of the proposed interpolator.
An Investigation of Heat Dissipation in High Speed Machining
Authors: Quan Yan Ming , Arsecularatne Joseph A. , Zhang Liang Chi
Published: September 2009

High speed machining (HSM) is finding wider applications due to its economic advantages, such as faster material removal rates, and its technological merits, such as improved surface finish. Nevertheless, the application of HSM also brings about some undesirable results. For example, the tool life and surface integrity of a machined component are greatly affected by the large amount of heat generated, but heat dissipation during an HSM has not been well understood. This paper aims to achieve a quantitative understanding of the heat dissipation in HSM using a bar turning configuration. Based on the calorimetric method and utilizing water as the heat transfer medium, the temperature rise in water was measured to determine the fractions of heat dissipated into the chips, the tool and the workpiece during machining. The obtained results show that the chips take the largest portion of the heat generated and this fraction increases with the increase in feed.
Machinability and Tool Wear Behavior in Turning High Nickel-Base Alloy-G3
Authors: Luo Meng , Zhang Li Qiu , Chen Ming
Published: September 2009

High nickel-base alloy, such as G3, is famous for its corrosion resistant, high intensity and other characteristic, which is popular in petroleum extraction and other heavy industry. However its poor machinability is a big obstacle to launching this material in its application. This paper introduces the poor machinability and tool wear behavior in turning high nickel-base alloy-G3. Based on rough and finished turning, turning experiments were carried out according on cutting speed, cutting depth, coolant and etc. some improved processes were suggested. This paper will be beneficial and guidable in turning high nickel-base alloy and other similar high nickel-base alloy or stainless steel.
Nano-Precision Synergistic Finishing Process Integrated ELID-Grinding and MRF
Authors: Yin Shao Hui , Ohmori Hitoshi , Lin Wei Min , Uehara Yoshihiro , Chen Feng Jun , Fan Y.F. , Zhu Yong Jian
Published: September 2009

ELID (electrolytic in-process dressing) grinding was proposed by one of the authors for automatic dressing the grinding wheel while performing grinding for a long time. It offers a high effective way and has been widely used for grinding hard and brittle optical materials. However, those surfaces produced by fixed abrasive grinding are characterized by considerable sub-surface damage, micro-crack. Magneto-rheological finishing (MRF) is a novel precision finishing process for deterministic form correction and polishing of optical materials by utilizing magneto-rheological fluid. In this paper, an ultra-precision synergistic finishing process integrated MRF and ELID grinding is proposed for shorten total finishing time and improve finishing quality. A lot of nano-precision experiments have been carried out to grind and finish some optical materials such as silicon, silicon carbide, etc. ELID grinding is employed to obtain high efficiency and high surface quality, and then, MRF is employed to improve further surface roughness and form accuracy. In general, form accuracy of ~ λ/20 nm peak-to-valley (P-V) and surface roughness less than 10 Angstrom are produced in high efficiency.
Optimization of Surface Roughness by Uniform Design of Experiments in Milling of 1Cr18Ni9Ti
Authors: Zhang H.Z. , An Qing Long , Zhang Yun Shan , Liu Gang , Chen Ming
Published: September 2009

This paper presents the optimization process of a surface roughness model for the milling 1Cr18Ni9Ti. The model is developed in term of milling speed, feed per tooth and radial depth of cut. Therefore, the regression model predicting formula for surface roughness has been established by means of uniform design of experiment, and then the response surface methodology was applied to generate response contours of surface roughness. The experimental results indicate that the material removal rate can be improved by selecting optimal milling parameters without increasing the surface roughness. Moreover, it is seen that the feed rate is the most significant factor on the surface roughness.
Development of Multilayer Composition Thin Film Thermocouple Cutting Temperature Sensor Based on Magnetron Sputtering
Authors: Cui Yun Xian , Sun Bao Yuan , Ding W.Y. , Sun F.D.
Published: September 2009

In the paper, a new multilayer composition thin film thermocouple was developed, which can accurately measure the temperature nearby cutting edge in convenient and fast ways. By means of advanced Twinned microwave ECR plasma source enhanced Radio Frequency (RF) reaction non-balance magnetron sputtering technique, SiO2 insulating film, NiCr/NiSi sensor film and SiO2 protecting film were deposited on the surface HSS substrate. Both static calibration and dynamic calibration were completed. The results showed that the sensor had good performance, good linearity, quick dynamic response, response time constant was 12.7ms. The temperature near the cutting edge in cutting process of aluminum alloy was measured by the developed sensor. The bonding strength between multiple layer film and substrate of high-speed-steel met the presupposed demands.
Design and Fabrication of the Micro Turbine for Micro Gas Turbine Engine
Authors: Dong Ying Huai , Wang Zhen Long , Peng Zi Long , Chen Hui , Zhao Wan Sheng
Published: September 2009

The designing of a micro turbine for micro gas turbine engine is presented in this paper. Micro power system is becoming more and more important for micro- and nano-scale system. The fast development of MEMS (Micro Electromechanical Systems) has strongly enhanced the application of new harder work materials. The fabrication of metallic 3D microstructures has been one of the most attractive topics of micro machining. Currently the basic materials of Micro-turbine Engineering were nonmetal materials such as SiC, most of them are 2D or quasi-3D structures. As a low cost, flexible, good repeatable machining process with negligible process forces, micro-EDM milling is well suited for freeform metallic micro structures. A three-dimensional micro turbine was fabricated by micro-EDM milling. A major problem in micro-EDM milling of complex 3D structure by using micro-electrode is the electrode wear. For reducing the impact of electrode wear, A new CAM system based on the UG software platform is developed in order to get good accuracy 2and higher efficiency. A simple tool path generation by CAD/CAM software and a general electrode wear compensation strategy is presented. The wear compensation can be apart from the design of CAD/CAM systems, so existing common CAD/CAM systems can be used to generate milling tool path with an unequal thickness lamination. And then post process for wear compensation and EDM milling can be done to modify tool path by adding wear compensation. The micro turbine blades of which the material is nickel alloy (GH4169) were successfully fabricated by using this strategy. The diameters of turbine are 2.8mm, and the height of each blade is 0.4mm.
Research on Remotely Operable PC-Based CNC System via Network
Authors: Hu Zi Hua , Liu J. , Zhao H.L. , Yuan Ju Long
Published: September 2009

This paper presents a remotely operable PC-based CNC (Computer Numerical Control) system via network aimed at remote control and real-time monitoring. The system is developed on the client-server architecture. Specially, for the sake of network bandwidth conservation and the requirement of on-line feedback, OpenGL technology is introduced as an alternative of the network camera-based solution for remote visualization. At last, a practical example is provided to demonstrate the feasibility of the developed CNC system.
Design and Fabrication of Silicon Condenser Microphone for Industrial Use
Authors: Dong J. , Wang Wei , Ji Shi Ming , Zhang L.B.
Published: September 2009

A single-chip silicon condenser microphone with a sandwich diaphragm and an electroplating perforated copper backplate has been developed. The sandwich diaphragm is designed to have a slight tensile stress. The backplate is made using copper electroplating technology and perforated with circular holes. Perforated circular holes on backplate are laid out as hexagon to adjust air-gap damping between diaphragm and backplate to critical damping to enlarge frequency bandwidth of microphone. Fabrication is simple enough and only needs five photolithography marsks. Measurements show the open-circuit with 9V bias voltage reaches 5.45mv/Pa in 1KHz, pull-in voltage is 14V, and the flat frequency response within 3Db is from 100Hz to 20KHz. The performances of microphone meet the requirement of industrial use. Thereby, it has promising prospect for industrial and commercial field.
Analysis of Workspace and Rotation Ability for a Novel Humanoid Robot Elbow Joint
Authors: Cui Bing Yan , Jin Zhen Lin
Published: September 2009

The workspace and the kinematic transmission play important role on the design and optimation of the eblow joint. In this paper, a novel humanoid robot elbow joint based on 2-DOF orthogonal spherical parallel mechanism is proposed. Position of elbow joint is analyzed using the vector method and projection theory. The kinematic balance equation of the eblow joint is established by analyzing the relationship of its input and output velocity. The kinematics transmission evaluation index and the global kinematic transmission evaluation index of the elbow are defined, and the distribution of the global kinematics transmission evaluation index in the workspace is drawn. And rotation ability of the elbow joint is analyzed. The analytical results indicate the elbow has advantages of big volume, smooth boundary, good kinematic transmission, strong rotation ability, which can provide theoretical base for the applications of the elbow.
Cutting Forces and Vibration of Pockets Corner by High Speed Milling
Authors: Wang Cheng Yong , Tang De Weng , Qin Zhe , Chen Z.G. , Hu Ying Ning , Song Yue Xian
Published: September 2009

When the pocket in die and mould is machined by high speed milling (HSM), the cutting forces increase and vibration fluctuates at the pocket corner because of the sudden change of cutting direction in general. It will cause serious wear and possible breakage of cutting tool, and poor quality of parts. By means of experiments, the cutting forces and vibration at the pocket corner with different HSM conditions are measured. The results show that the sharper pocket corner, higher cutting speeds, larger feed rate per tooth and radial depth of cut, will result in increasing of cutting forces and vibration amplitude. Thus, it will lead to be unstable during the process of high speed milling pocket corner.
Modeling and Analysis of the Structure of Superpave Gyratory Compactor
Authors: Jiang Wei , Qiu X.G. , Chai Guo Zhong , Zhou Jian Xing
Published: September 2009

Superpave Gyratory Compactor (SGC) is used to design high quality mix asphalt specimen. In this research the structure of the SGC was analyzed, and the methods used in the Stewart mechanism are adopted. Based on the hypothesis that the parts made up of the mechanism are rigid body, no deformation exists in the connecting rods. Equations are deduced and the position is presented. The positions of the joint are acquired from the equations by MATLAB. Finally the elements that affect the title angle between the swivel panel and the perpendicular z axis are calculated, and the optimal parameters are presented.
Research of the Pressure Pulsation within Piston Chamber in Radial Piston Pump
Authors: Jiang Wei , Qiu X.G. , Chai Guo Zhong , Zhou Jian Xing
Published: September 2009

Noise reduction in piston pumps has been being the focus research. Many methods have been designed to smooth it. Research shows that noise takes place at the time when pistons enter the discharge port or enter the suction port. In fact, noise is induced by imbalance pressure in piston chamber. In this paper, piston initial volume and instantaneous controlled volume are deduced. Equations describing pressure angle-rate-of-change are also deduced. Keep the pressure increment equal when the pump eccentric distance is maximum and minimum, and then find out the optimal structure parameters. The parameters makes the pressure ripple minimize and makes the lowest noise.
Magnesium Alloy Material Substitution Redesign Method for Wheels of Electric Bicycle
Authors: Pan Bai Song , Gong H.L. , Peng Ting Hong , Zhang Miao
Published: September 2009

For the excellent characters such as lightweight, high ratio-strength, high rigidity and reuse, magnesium alloy is used widely in vehicle lightweight redesign. Selecting AM60B as material, the process of magnesium alloy material substitution redesign for wheels of electric bicycle is advanced. The structure of aluminum alloy wheel is chosen as prototype structure for magnesium alloy wheel according to the similarity between the properties of aluminum alloy and magnesium alloy. The structure redesign optimized parametric model is put forward by the stimulation analysis of static load test and dynamic bending fatigue test. The inspection of samples shows that the structure redesign is feasible, and the target of wheels lightweight redesign is achieved.
The Simulation Design of the Rotary Valve of Hydraulic Power Assisted Steering System Based on the VB
Authors: Zhou Qu Zhu
Published: September 2009

That automobile steering system are designed to suitable or not have a direct impact on vehicle safety, handling stability and driving comfort.The rotary valve of hydraulic power assisted steering system is one of the key components which affects the automotive steering performance. Design a reasonable spool valve in size can allow the car to get good properties . In this paper we use Visual Basic 6.0 to make a design calculations on rotary valve firstly, and then use the VB to carry out the numerical simulation on the steering performance of rotary valve and fitting the performance curve secondly, This method raised the design precision of the rotary valve, the design calculations is simplified.
Review of Gas-Assisted Injection Molding Process
Authors: Jiang Shao Fei , Lu Cong Da
Published: September 2009

The forming mechanism and optimization of the gas-assisted injection molding (GAIM) process have been studied for several years, both at home and abroad. Some researches and experiments about GAIM is summarized in this paper. The GAIM's forming mechanism focuses on research of the filling, gas-assisted filling and gas-assisted packing and cooling stages. While the optimization of the GAIM process pays much more attention to one of the parameters affecting the molding quality.
Research of Quickly Dry Equipments about Chinese Herbal Medicine
Authors: Nan Xiu Rong
Published: September 2009

To analyze the Chinese herbal medicine drying system, vacuum and microwave technique, function principle and method are introduced in the paper. The necessity of the system is also put forward. The technology of the Chinese herbal medicine quickly drying in vacuum and microwave is studied and the principle of the design is introduced. Practical usage of the system shows that the equipment is full of good practicability and economic benefit.
A Tension Control Approach to the Multi-wire Saw Based on DSP
Authors: Peng S.Q. , Dai Y.X. , Zhang Y.B. , Jiang Jin , Yuan Ju Long
Published: September 2009

Multi-wire sawing is a novel method for slicing silicon. The tension control of wire is a vital factor that has impaction on the slicing process. Along with the modern wind machine developing to higher speed and precision, tension control technology becomes more important. This paper introduces a closed-loop tension control system with the digital signal processor (DSP) with function modules as its control kernel, the alternating current (AC) servo motor as execute element and the radius-following device to accomplish the real-time radius compensation. The mechanism of the tension control system is analyzed and the numerical model is set up. The compensation technique of the radius of the scroll is analyzed. Experimental results show that the system is well qualified with high control precision and high reaction speed.
A Fast Algebraic Grid Generation Algorithm Base on an Improved Kamaugh Map
Authors: Xiu Shu Dong , Ji Shi Jun , Wang Yang
Published: September 2009

A fast algebraic grid generation algorithm is proposed and a improved Kamaugh map data structure for the new algorithm is designed in the paper. The new created vertex inside of the region is based on algebraic operation of the corner vertices and the middle vertices of boundary broken lines on the region and the program data structure is a improved Kamaugh map data structure, so the algorithm has the merit of simple algebraic formula, quickly executing speed and powerful technology for the four-sided region enclosed by four broken lines, the algorithm is realized on the four-sided region and B-spline surface on the complex surface. The algorithm is extensively applicable for shape modeling in computer aided geometric design, industrial prototype design and reverse engineering.
Study of Active Vibration Control for Flexible Beam’s Vibration
Authors: Zhang Li , Ji Shi Ming , Xie Yi , Yuan Qiao Ling
Published: September 2009

The attenuation of structure vibration is very slow when flexible strucure is stirred external force. It seriously affected the life of flexible structure. Smart structures used piezoelectric ceramics as actuators are an effective manner to solve the problem. This paper uses Fiber Bragg Grating (FBG) as sensors and piezoelectric ceramics as actuators to study the active vibration control for the resonance of the smart beam. Two groups of piezoelectric ceramics will be used for vibration exciter and vibration abatement, respectively. The fiber smart beam is excited to a sharp vibration nearby the particular resonance frequency by controlling the frequency of the vibration excitation. The vibration signal is measured by the FBG sensors and the close loop feedback control is fulfilled by the vibration abatement group, and the vibration amplitude of the fiber smart beam is abated. The experiment results show that the resonance amplitude of the beam is obviously abated by adjusting the frequency, amplitude and phase of the vibration abatement circuit.
Workflow Simulation Modeling Based on Discrete Event Approach
Authors: Miao Y.P.
Published: September 2009

In order to apply simulation to analysis, evaluation and optimization of the workflow performances, workflow process model for simulation is firstly formalized. Then workflow simulation model is bulit based on discrete event approach. Finally the supporting software tool system has been developed which shows feasibility of the proposed method.
Effect of Free Abrasive Particle in Gasbag Polishing Technique
Authors: Jin Ming Sheng , Ji Shi Ming , Zhang Li , Zhang Xian , Shen Ya Qi
Published: September 2009

Free abrasive particle plays a crucial role in material removal and quality improvement of curved surface mould. In order to observe and investigate the general distribution state, fractal dimension and movement characteristic of abrasive particle in gasbag polishing process better, an abrasive particle stroboscopic photography system is established and polishing experiment is carried out. The abrasive particle contacts with not only the rubber gasbag enwrapped by polishing cloth full of mesh-like structures, but also the mould surface. Contact analysis of abrasive particle including the discussions of contact state, material removal mechanism and advantage of precession polishing is helpful to hold the optimal polishing process parameters combination and establish ideal abrasive particle field for higher polishing efficiency and more well-proportioned surface quality.
An Effect Contrast for Chemical Mechanical Polishing with Mechanical Polishing for Tungsten Steel
Authors: Zhang Ke Hua , Wen Dong Hui
Published: September 2009

The interaction between the tungsten steel surface and the polishing fluid & abrasive were discussed by AFM, SEM and XRD test in order to compare the chemical performances and mechanical action of the tungsten steel polishing in the paper. The chemical mechanical polishing (CMP) and the mechanical polishing (MP) was employed, respectively. The experiments results indicated that the CMP with a higher the materials removal ratio than by MP. Because a chemical corrosion effect implies that slurries with the highest removal rate have high dissolution rate, and have a lower the residual stress, however the surface took on wrinkling.
Characterization of the Anoxic Sediments of Rio Tinto: Biohydrometallurgical Implications
Authors: García-Moyano A. , González-Toril E. , Amils R.
Published: September 2009

Rio Tinto, a natural extreme acidic environment with a rather constant acidic pH and a high concentration of heavy metals, is the product of the metabolic activity of chemolithotrophic microorganisms thriving in the rich complex sulfides of the Iberian Pyritic Belt. Up to now the microbial characterization has been made mainly in the water column and biofilm samples. Since all ferric reducing activities will not benefit the bioleaching operations, we consider it critical to ascertain the ecology and metabolic properties of the microorganisms inhabiting the anoxic part of the sediments, to facilitate the design and control the operation of heap bioleaching processes, maximizing their efficiency. The implication of these microorganisms in biohydrometallurgical operations is discussed.
Microbial Impact on Arsenic Mobilization in Zloty Stok Gold Mine
Authors: Drewniak Lukasz , Matlakowska Renata , Sklodowska Aleksandra
Published: September 2009

The aim of this review report was to summarize knowledge about arsenic-metabolizing bacteria isolated from Zloty Stok (SW Poland) gold mine and determine their potential role in mobilization of arsenic.
Three physiologically different groups of arsenic metabolizing microorganisms (arsenite oxidizers, dissmiliatory arsenate reducers and arsenic resistant microbes) were isolated from the deepest section of Gertruda Adit in Zloty Stok (SW Poland) gold mine. Twenty two strains were isolated from the rock biofilms and seven from arsenic-rich bottom sediments. Analysis of the 16S rRNA gene sequence of isolated bacteria revealed them to be members of the genera: Aeromonas, Arthrobacter, Bacillus, Brevundimonas, Chryseobacterium, Desemzia, Microbacterium, Micrococcus, Paracoccus, Pseudomonas, Rhodococcus, Serratia, Shewanella, Sinorhizobium, Sphingomonas, Stenotrophomonas and Streptomyces. All of the isolated bacteria were resistant to both inorganic arsenic species: arsenate [As(V)] and arsenite [As(III)]. One of the bottom sediments isolates (Sinorhizobium sp. M14) was able to grow on minimal salt medium using arsenite as a source of energy, and was able to release arsenic from arsenopyrite. Two strains (Shewanella sp. O23S and Aeromonas sp. O23A) isolated from bottom sediments were able to grow in the absence of oxygen, by As (V) respiration coupled with lactate oxidation. Based on arsenic metabolic activity of isolated bacteria two different mechanisms of arsenic mobilization from natural minerals (arsenopyrite FeAsS) and secondary ferrous arsenate minerals (scorodite FeAsO4) were proposed.
Analysis of Sulfur Metasecretome in Mixed Cultures of Acidithiobacillus Thiooxidans and Acidithiobacillus Ferrooxidans
Authors: Bobadilla Fazzini R.A. , Parada Valdecantos Pilar
Published: September 2009

The role of biomolecules in bioleaching of copper sulphide minerals carried out by bacterial consortia with predominating acidithiobacilli species is of outmost interest. The proteomic analysis on bioleaching bacterial strains have been focused up to date on full Acidithiobacillus ferrooxidans proteome, allowing the identification of proteins belonging to the general stress response, phosphate limiting conditions and the ones linked to the periplasmic fraction. Our study shows for the first time the differential expression of secreted proteins by means of standard proteomics between pure cultures of Acidithiobacillus thiooxidans and in mixture with A. ferroxidans (metasecretome) grown in sulfur, where a set of proteins is de novo synthesized in the mixed culture, identifying an Omp40-like protein possibly related to bacterial adhesion, an hypothetical protein PSEEN2944 with unknown function and up-regulation of a cytochrome c biogenesis protein, findings that give an insight into the role of proteins at the sulfur – bacteria interface, highlighting the outputs of bacterial interactions in biomining environments at the protein secretion level.
Regulation of the Iron and Sulfur Oxidation Pathways in the Acidophilic Acidithiobacillus Ferrooxidans
Authors: Amouric A. , Appia-Ayme C. , Yarzabal A. , Bonnefoy Violaine
Published: September 2009

The acidophilic and strictly chemolithoautotrophic bacterium Acidithiobacillus
ferrooxidans oxidizes ferrous (Fe(II)) to ferric (Fe(III)) iron and reduced inorganic sulfur
compounds (RISC) to sulfuric acid, in oxic conditions. The redox proteins involved in the electron
transfer between Fe(II) and oxygen are encoded in the same transcriptional unit, the rus operon. The
expression of this operon is induced in the presence of Fe(II), but not Fe(III), and is not repressed in
the presence of sulfur (S0). A number of genes differentially expressed in iron or sulfur conditions
have been identified by microarrays transcript profiling. We show here that the presence of Fe(II)
induced the expression of the genes involved in iron oxidation and repressed the expression of the
genes involved in RISC oxidation. Identification of the regulator(s) involved in this transcriptional
regulation is underway. Two genes encoding putative regulators belonging to two transcriptional
units located downstream from the rus operon have been cloned. One regulator with a putative ironsulfur
cluster belongs to the IscR family and the other belongs to the two component
sensor/regulator family. Expression of both genes is induced in the presence of Fe(II) and is not
repressed by S0. The recombinant proteins have been purified and gel shift assays with the target
regulatory regions are in progress.
A Preliminary Differential Proteomic Analysis of the Periplasmic Fraction in Acidithiobacillus Ferrooxidans Planktonic and Attached Cells Exposed to Chalcopyrite
Authors: Felício Ana P. , de Oliveira Eliandre , Odena M.A. , Garcia Jr. Oswaldo , Bertolini Maria C. , Ferraz Lúcio F.C. , Ottoboni Laura M.M. , Novo Maria T.M.
Published: September 2009

The Acidithiobacillus ferrooxidans periplasmic space is known to have proteins involved in the respiratory chains. There are no reports about the expression of the periplasmic proteins in A. ferrooxidans cells attached to chalcopyrite. In this preliminary work, it was compared the periplasmic protein profiles of A. ferrooxidans planktonic and attached cells after exposure to chalcopyrite for 2 hours. The bacterial response to chalcopyrite was investigated by a proteomic approach (two- dimensional gel electrophoresis and mass spectrometry). Four proteins differentially expressed between planktonic and attached cells after exposure to chalcopyrite were identified. Two of these proteins, repressed in chalcopyrite- attached cells, were both identified as superoxide dismutase, whereas the single strand binding protein (SSB) and the PspA/IM30 protein were induced. These results showed that A. ferrooxidans chalcopyrite- attached and planktonic cells show differential expression of the periplasmic proteins and that a proteomic approach can provide a valuable tool to detect proteins related to the A. ferrooxidans response to attachment to the mineral substrates.
The Secretome of the Extremophilic Acidithiobacillus Ferrooxidans ATCC 23270
Authors: Pagliai F.A. , Jerez Carlos A.
Published: September 2009

Acidithiobacillus ferrooxidans is a chemolithoautotrophic acidophile capable of catalyzing the oxidation of ferrous iron and sulfur reducing compounds. During the dissolution of ores A. ferrooxidans adheres to the solid substrate by hydrophobic and hydrophilic interactions and also extracellular polymeric substances may be involved. Nevertheless, many of these agents that participate in the process are unknown. Therefore, the identification and characterization of the extracellular proteome of A. ferrooxidans was addressed during this work. First, by searching the genome of A. ferrooxidans ATCC 23270 the putative genes coding for proteins present in most of the different secretion systems (type I, II, IV, V systems and the Usher pathway) were found. Second, when the secretion signal prediction server SubCel 1.0 was used, 26.7 % of the total open reading frames showed possible signals that would allow these proteins to leave the cytoplasm towards the internal and outer membranes, the periplasm, or the extracellular milieu. By using 2D-NEPHGE and MS sequencing we identified the eleven most abundant proteins present in the extracellular fraction. Proteins related to the transport and binding of solutes and the folding of proteins, among others were identified. Along with the non-classical pathway, the protein secretion systems identified could constitute the secretion machinery for the proteins found in the extracellular sub-proteome of A. ferrooxidans that as a whole constitute its secretome. Further studies of the extracellular proteins from this biomining microorganism will be important to find out their possible role if any, during bacteria-mineral interactions.
Prediction of FNR Regulated Genes and Metabolic Pathways Potentially Involved in Anaerobic Growth of Acidithiobacillus Ferrooxidans
Authors: Osorio Hector , Cárdenas Juan Pablo , Valdés Jorge H. , Holmes David S.
Published: September 2009

Efficient bioleaching requires adequate access to oxygen to drive the biochemical reactions that underpin iron and sulfur oxidation and ultimately copper solubilization. However, microaerophilic or anaerobic conditions may occur in certain parts of the heap, especially in areas of intense microbial activity or in biofilms where oxygen gradients occur. Microaerophilic conditions have also been detected in pristine acidic environments and in abandoned bioleaching operations. An important microorganism in bioleaching at ambient temperatures is the chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans. In addition to its well established role in oxidative processes, it has been shown to be capable of reducing metals such as iron and sulfur, and the products of these reactions may promote passivation of mineral surfaces and impede efficient solubilization of copper. In an effort to advance our understanding of the genetic and physiological basis of anaerobic metabolism, gene clusters controlled by the master anaerobic transcriptional regulator FNR were predicted in the genome of A. ferrooxidans using bioinformatics techniques. These clusters were found to be associated with energy metabolism, nitrogen fixation and carbohydrate metabolism. The results not only support previous evidence for proposed anaerobic metabolic pathways but also identify new genetic components and pathways that may be important for anaerobic or microaerophilic growth of this microorganism.
Regulation of Expression of the PetI Operon Involved in Iron Oxidation in the Biomining Bacterium Acidithiobacillus Ferrooxidans
Authors: Lefimil C. , Osorio Hector , Quatrini Raquel , Holmes David S. , Jedlicki Eugenia
Published: September 2009

Acidithiobacillus ferrooxidans is an acidophilic, chemolithotrophic bacterium that can gain energy and electrons by the oxidation of iron. PetI is an operon that encodes electron transport proteins involved in the reverse flow of electrons from iron to the NAD complex during iron oxidation. Although a substantial body of evidence describes the components and pathways for iron oxidation, little is known about their regulation. It is proposed that environmental iron concentrations and oxygen levels could influence the ability of A. ferrooxidans to oxidize iron as an energy source. We report initial investigators into the possibility that the expression of the PetI operon is regulated, inter alia, by the master transcription factor controlling iron uptake and homeostasis (Fur) and anaerobic metabolism (FNR). Potential DNA binding sites (boxes) for both regulators were predicted in the region of the PetI operon promoter and the binding of Fur to its cognate box was demonstrated experimentally. This represents the first attempt to unravel the mechanisms involved in the regulation of iron oxidation.
Genomic Lessons from Biomining Organisms: Case Study of the Acidithiobacillus Genus
Authors: Valdés Jorge H. , Holmes David S.
Published: September 2009

Advances in DNA sequencing technologies have promoted the use of genome information as a key component in most of biological studies. In the case of biomining microorganisms, partial and complete genome information has provided critical clues for unraveling their physiology. This information has also provided genetic material for the generation of functional and biodiversity directed markers. In this work, we present a compilation of the most relevant findings based on genomic analysis of the model organism Acidithiobacillus ferrooxidans ATCC23270 that were extended and compared to the recently sequenced genomes of Acithiobacillus thiooxidans and Acidithiobacillus caldus. The phylogenetic relatedness of these three microorganisms has permitted the identification of a shared genomic core that encodes the common metabolic and regulatory functions critical for survival and proliferation in extremely acidic environments. We also identified microorganism-specific genomic components that are predicted to be responsible for the metabolic speciation of these microorganisms. Finally, we evaluated the impact of lateral gene transfer on these genomes in order to determine the functional contribution of this phenomenon to the fitness of these microbial representatives. The information gathered by genomic analyses in the Acidithiobacillus genus will be presented in conjunction with other biomining genomic and metagenomic information in order to generate a more comprehensive picture of the biodiversity, metabolism and ecophysiology of the bioleaching niche.
Differential Gene Expression of Industrial Bioleaching Transcriptomes by Leptospirillum Ferrooxidans DNA Microarray
Authors: Remonsellez Francisco , Moreno-Paz M. , Parro V. , Demergasso Cecilia
Published: September 2009

Heap bioleaching is presently the most successful technology for copper extraction from low-grade sulfide ores. Metabolic behaviors and adaptation mechanisms of microbial communities to this system remain unknown. A combination of molecular approaches has been used to determine the key microorganisms in the Escondida Sulphide Heap. This work reports the global gene expression in industrial bioleaching samples by using a specific DNA microarray of Leptospirillum ferrooxidans to better understand the metabolic functions displayed by Leptospirillum spp. iron oxidizers as mineral leaching proceeds. Quantitative real-time PCR analysis showed low cell numbers of Leptospirillum species during the first part of the irrigation period, however, it became the most abundant and active in the second part of the cycle. Transcriptome analysis by DNA microarray could provide specifics transcription patterns in the different stages of the industrial process. We studied the gene expression from bioleaching heap samples with variable Leptospirillum cell numbers, operation times and with different chemical and physical conditions. The results showed induction of genes involved in energetic metabolism, electron transport, ribosomal proteins, DNA repair and response to heavy metals when Leptospirillum species were most abundant and active. We suggest that up- and down-regulation of specifics genes could be used as indicators of physiological responses to operational conditions in the bioleaching systems.
Sulfur Oxygenase Reductase in Different Acidithiobacillus Caldus-Like Strains
Authors: Janosch Claudia , Thyssen Christian , Vera Mario A. , Bonnefoy Violaine , Rohwerder Thore , Sand Wolfgang
Published: September 2009

The elemental sulfur oxidising enzyme Sulfur Oxygenase Reductase (SOR) is very well investigated in acidothermophilic archaea, such as Acidianus brierleyi and Sulfolobus metallicus. In contrast, not much is known about the biochemistry of elemental sulfur oxidation in acidophilic bacteria. Recently, however, the SOR-encoding gene has been found also in a bacterial strain closely related to the moderate thermophile Acidithiobacillus caldus. Confusingly, for the latter species, also the involvement of the SOX system as well as thiosulfate:quinone oxidoreductase (TQO) and tetrathionate hydrolase (TTH) in sulfur compound oxidation has been proposed based on genome analysis. In this study, we have detected the sor-gene in other Acidithiobacillus caldus-like strains, isolated from various bioleaching habitats, indicating that SOR plays an important role in sulfur oxidation in this species. Based on sequence comparison, the new bacterial sor-genes are closely related and distant from the known archaeal sequences as well as from the SOR found in the neutrophilic bacterium Aquifex aeolicus. In addition, SOR activity has been detected in crude cell extracts from all Acidithiobacillus caldus-like strains tested. The enzyme is truly thermophilic as highest activities were achieved at 65 °C, which is far beyond the growth optimum of Acidithiobacillus caldus. This finding may give rise to the question whether the presence of SOR in Acidithiobacillus caldus is only relevant while growing at elevated temperatures. Currently, experiments are performed for testing this hypothesis (comparing growth and enzyme activities at 30 vs. 45 °C).
Reduction of Cytochrome c by Tetrathionate in the Presence of Tetrathionate Hydrolase Purified from Sulfur-Grown Acidithiobacillus Ferrooxidans ATCC 23270
Authors: Taha Taher M. , Takeuchi Fumiaki , Sugio Tsuyoshi
Published: September 2009

It is mysterious that, when A. ferrooxidans ATCC 23270 cells grow on elemental sulfur, they have high iron oxidase activity comparable to that of iron-grown cells as well as high activities of sulfide:ferric ion oxidoreductase (SFORase) and tetrathionate hydrolase. To clarify this interesting phenomenon, cytochrome c and tetrathionate hydrolase were purified from sulfur-grown A. ferrooxidans cells using ammonium sulfate precipitation, Phenyl column chromatography, and SuperdexTM 75 and Sephadex G-100 size exclusion column chromatographies. The purified cytochrome c was reduced by tetrathionate in the presence of purified tetrathionate hydrolase, but not in the absence of the enzyme. When the partially purified cytochrome c fraction containing aa3-type cytochrome oxidase was used, both cytochrome c and aa3-type cytochrome oxidase were reduced by tetrathionate in the presence of purified tetrathionate hydrolase. These results indicate that tetrathionate in the presence of tetrathionate hydrolase can reduce iron oxidase enzyme system containing cytochrome c and aa3-type cytochrome oxidase as tetrathionate hydrolase decomposes tetrathionate to produce thiosulfate, elemental sulfur, and sulfate; and the formed thiosulfate can chemically reduce cytochrome c and Fe3+.
Kinetics of Ferrous Iron Oxidation by Leptospirillum Ferriphilum at Moderate to High Total Iron Concentrations
Authors: Penev K. , Karamanev D.
Published: September 2009

The effects of temperature, pH and iron concentration on the kinetics of ferrous iron biooxidation by a free suspended culture of Leptospirillum ferriphilum were studied in shake flasks and a circulating bed bioreactor at moderate to high total iron concentration. The kinetic study showed that there are two distinct modes of iron biooxidation: growth associated and non-growth associated, depending on the pH of the medium. There were also distinctive maxima of the effect of temperature and pH on the rate of biooxidation. A kinetic model of the process was proposed, based on an electrochemical-enzymatic model. The proposed model indicates that at moderate to high concentrations (above ~12 g/L), the total iron concentration becomes the single most prominent inhibiting factor.
Experimental Study of Ferrous Iron Biooxidation by Leptospirillum Ferriphilum in Different Biofilm Reactors
Authors: Svirko L. , Bashtan-Kandybovich I. , Karamanev D.
Published: September 2009

The process of biological oxidation of ferrous iron by the microorganism Leptospirillum ferriphilum was studied in different types of biofilm reactors. A total of 12 bioreactor types with both fixed and mobile support were used. The biofilm supports used had different shapes and were made of: polyethylene, nylon, polystyrene, polyvinylidene difluoride, polyester, ceramics, carbon and PVC. The pH of the microbial medium was maintained around 1.0, the temperature was 40°C while the influent ferrous iron concentration was 20 g/L. Iron oxidation rates of up to 4.5 g/L/h were obtained. The most efficient were the bioreactors with polyethylene and nylon woven fabric support. However, they oxidized ferrous iron at high rate for relatively short time periods - 40 to 60 days. While the bioreactor with a fixed bed of Raschig rings support had lower iron oxidation rate, their long-term stability was much higher. Of all the biofilm support materials tested, it was found that only polyvinylidene difluoride did not allow the formation of biofilm. Since no significant amounts of jarosite were formed at pH of 1.0 and below, the biofilm formed was very weak mechanically. For that reason the moving support, such as inverse fluidized bed, was not very appropriate because of the high shear stress.
ATP Measurements in Iron-Oxidizing Acidithiobacillus Ferrooxidans
Authors: Mandl Martin , Markova Romana , Lojek A.
Published: September 2009

We applied a kit for bioluminescent ATP measurement based on the luciferase reaction to Acidithiobacillus ferrooxidans cultures. Determination limit for monitoring cell growth in the culture was 1.1 × 106 cells per ml. Determination errors varied between 1.5 and 10 % (RSD). ATP formation correlated with cell growth and iron oxidation up to limitation by iron(II). A maximum ATP content was approximately 1 amol per cell under the growth yield on iron of 1 × 1012 cells per mol Fe(II).
The Characterization of Salt Tolerance in Biomining Microorganisms and the Search for Novel Salt Tolerant Strains
Authors: Zammit Carla M. , Mutch L.A. , Watling Helen R. , Watkin Elizabeth L.J.
Published: September 2009

In this study an acidic saline drain in the Western Australian wheat belt was sampled and enriched for salt tolerant chemolithotrophic microorganisms in acidic media containing up to 100 gL-1 NaCl. A mixed consortium was obtained which grows at pH 1.8 and oxidises iron (II) in the presence of up to 30 gL-1 NaCl. In comparative tests (growth rates and iron (II) oxidation rates) it was found that NaCl concentrations >3.5 gL-1 generally cause reduced growth and iron (II) oxidation rates in known biomining organisms. The results help to set a benchmark for NaCl tolerance in known biomining microorganisms and will lead to the generation of a consortium of microorganisms that can oxidise iron (II) effectively in saline process water.
Biohydrometallurgy: What is its Future?
Authors: Brierley Corale L.
Published: September 2009

Bioleaching/minerals biooxidation and bioremediation have been widely used commercially for heap/dump bioleaching of secondary copper sulfide ores, sulfidic-refractory gold concentrates and treatment of acid rock drainage. Technical and commercial challenges, identified in this paper, remain for bioleaching of primary sulfides and complex ores. New frontiers for the technology exist in processing massive sulfides, silicate-locked minerals and in the more distant future in-situ leaching. Decommissioning of cyanide heap leach operations and stabilizing mine wastes using biotechnology are opportunities requiring intensive and focused research, development and engineering efforts.
From Laboratory to Application Heap Bioleach or not
Authors: Brierley James A. , Kuhn M.C.
Published: September 2009

The importance of comprehensive laboratory evaluation for development of an ore body to commercial processing using biohydrometallurgy cannot be understated. Laboratory evaluation for a biohydrometallurgical process must include the microbiological component and definition of operating parameters for the engineers to design the commercial plant. Failure to meet commercial production at a mine site can be a consequence of incomplete understanding of biohydrometallurgical technologies for processing a specific ore. One example is the inability of a copper bioleach process to meet the design criteria in part because of lack of sufficient testing to demonstrate the ramifications of fluoride toxicity to the microbial component of the bioleach process. Laboratory research has demonstrated toxicity of low levels of fluoride to Acidithiobacillus species. However, laboratory determined toxicity values are not always relevant to field conditions at commercial bioleach operations. This is the case with fluoride toxicity where complexing reactions increase the amount of fluoride required for toxicity. Consequently, the toxic fluoride concentrations at field sites can be significantly higher than toxic levels reported in the laboratory, but still achieve concentration inhibitory for the microorganisms.