bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital Hydraulics: A Theoretical Study Comparing Hydraulic Power Units
Authors: Manring Noah D.
Published: November 2016

Recent research has been used to identify efficiency improvements that may be obtained by utilizing on-off hydraulic valves in the place of traditional hydraulic valves. These efficiency improvements reduce throttling losses in the valve by using wide-open valve positions that are intermittently turned on and off. While this efficiency idea has emerged with great interest among some, there are still those who remain doubtful about the efficiency improvements that have been claimed and anecdotal concerns continue to be voiced at conferences and in hallway discussions within industry. This paper is being written to address the subject from a theoretical perspective. In the analysis of this paper, the efficiency equations for an on-off valve will be derived and compared to the efficiencies of valves that are employed in pressure relief systems, pressure compensating systems, and load sensing systems. In conclusion, it is shown that valves operating in load sensing systems are always the most efficient valves, while digital valves are often the next most efficient design except during low flow conditions when the valve in a pressure compensating system may occasionally be more efficient than the digital valve. It is shown in this research that valves used in pressure relief systems are always the most inefficient design.
Multi-Level Pressure Switching Control and Energy Saving for Displacement Servo Control System
Authors: Yao Jing , Cao Xiaoming , Wang Pei , Kong Xiangdong
Published: November 2016

For the huge energy losses of the conventional hydraulic valve-controlled servo control system, a new Multi-level Pressure Switching Control System (MPSCS) was coined and proposed in this study to address this issue. First, the discrete force distribution and switching rules of MPSCS was designed for conducting the four-quadrant working principle. Second, the hybrid control strategy was designed and applied for a displacement control system with three-level pressure rails. Finally, an experiment rig was established to validate proposals above in this study. The experimental results approved the pump input power and throttling losses of MPSCS was decreased dramatically compared with the conventional displacement control system, but the response time, position jitter etc. were still challenges to MPSCS.
An Energy-Saving Way to Balance Variable Negative Load Based on Back-Stepping Control With Load Observer
Authors: Mengren Jin , Qingfeng Wang
Published: November 2016

Traditionally, counterbalance valve (CBV) is widely used to counterbalance negative load of fluid power machinery. CBV introduces extra energy consumption and oscillation to hydraulic system especially for time varying system. The essence of its shortcoming is the inflexibility of the control architecture. In this article, a proportional orifice is adopted to counterbalance negative load, which makes the control strategy flexible. A load observer is proposed to demonstrate the load dynamically. A control algorithm based on back-stepping design is proposed in this paper afterwards, aiming at keeping the inlet chamber pressure of the actuator around a fairy small value. The control error is estimated, as well. A simulation for the process of the excavator booming down is carried out to verify the observer and control algorithm, which proves the energy-saving target achieved.
Influence of Anisotropic Surfaces on the Friction Behaviour of Hydraulic Seals
Authors: Angerhausen Julian , Murrenhoff Hubertus , Dorogin Leonid , Scaraggi Michele , Lorenz Boris , Persson Bo N. J.
Published: November 2016

In the modelling of the leakage rate, friction force or contact pressure distribution of hydraulic seals is quite common to assume the mating surfaces to be characterized by a random isotropic roughness. However, due to different surface finishing methods, such as coating, grinding or polishing, roughness with anisotropic characteristics is often generated.

In this paper a first experimental investigation of the influence of such anisotropic surfaces on the sliding friction is provided. For this purpose, a test rig has been designed and set up to investigate a soft, lubricated line contact representative of a generic reciprocating hydraulic seal. In particular, an O-ring cord is squeezed into contact with a steady rotating rigid cylinder. In order to adopt a cylinder-on-flat configuration, the diameter of the rigid cylinder is chosen to be significantly larger than the O-ring (cross-section) diameter. Furthermore, three cylinders with different surfaces are used: One (sandblasted) isotropic surface and two anisotropic surfaces roughness, scratched perpendicularly or along the azimuthal direction. Therefore, under temperature control, Stribeck curves have been measured at different squeezing loads and surface roughness, showing a neat influence of the surface roughness characteristics on the friction force. Finally, the experimental results are compared with the predictions provided by a recent mean field theory of soft contact (e.g. rubber) lubrication.
Simulation and Experimental Investigations of a Digital High Speed Close Loop Proportional Directional Valve Using a Solenoid Technology
Authors: Buono Dario , Senatore Adolfo , Frosina Emma , Gehlhoff Wade , Costin Ina I.
Published: November 2016

This paper describes the design, simulation and testing of a high response servo-proportional valve. The purpose of this work is to study the possibilities, using a modeling technology, to increase the dynamic performance of a servo-proportional directional developing new algorithms for the digital control system.

The development of digital technology, introduced also in the control of proportional valves, have led to the reduction of the differences between the overall characteristics of proportional and servo valves so that the proportional ones can be a suitable solution in many applications, where servo-valves are traditionally used.

The mathematical model of the servo-proportional valve has been developed by using the commercial software AMESim® (Advanced Modeling and Simulation Environment for Systems Engineering). The model includes the proportional solenoid and the linear transducer.

Digital control of the proportional valve proposed in this paper, is a key part of this research. Its mathematical model and the control algorithm have been built using Matlab®. Both models have been run in co-simulation to improve the overall valve performance.

The experimental tests have been performed in the labs of Duplomatic Oleodinamica SpA and Continental Hydraulic Inc.

The data have been used to validate the simulation models.
A Numerical Investigation of a Miniature Pneumatic Spindle Turbine
Authors: Harris Paul , Linke Barbara , Spence Stephen
Published: November 2016

The design and numerical simulation of a radial inflow turbine for a micromachining spindle is described. The spindle design specifications require the turbine stage to produce approximately 120W of power at a nominal design speed of 100,000 rpm. The aerodynamic and structural performance of the turbine stage is assessed using Computational Fluid Dynamics (CFD) and Finite Element (FE) simulations. A number of options to reduce rotor weight and inertia while maintaining high efficiency are investigated. Finally, as machine tool spindles are typically required to operate over a wide range of torque loads and speeds, the part-load aerodynamic performance of the turbine is also assessed.
Application of DDVC Fuel Injection System to Ship Speed Control
Authors: Sanada Kazushi , Miyazaki Tetsuro
Published: November 2016

This paper describes an application of direct drive volume control (DDVC) to ship speed control. The DDVC fuel injection device consists of an AC servo motor, a fixed-displacement oil-hydraulic pump, and an oil-hydraulic cylinder. The cylinder piston pushes a fuel pump to pressurize fuel and an injection valve opens to inject fuel into a combustion chamber. Timing and the quantity of fuel injection can be controlled by the electric signal added to the AC servo motor. In this paper, the DDVC fuel injection device is applied to engine speed control of marine diesel engine and ship speed control. A simulation model is made including a model of the DDVC fuel injection device, propeller model, and hull motion model. Firstly, engine speed control system is proposed. Stop injection angle is automatically adjusted according to engine speed error signal. Secondarily, ship speed control is proposed. Propeller pitch angle is used to control ship speed. Simulation study of these control systems are presented to show the capability of the DDVC fuel injection device for marine diesel engine.
Study of Air Inclusion in Lubrication System of CVT Gearbox Transmission With Biphasic CFD Simulation
Authors: Ferrari Cristian , Marani Pietro
Published: November 2016

The focus of this paper is the biphasic phenomena that occurs in a lubrication system of a CVT gearbox transmission of an agricultural tractor, in particular a Method of Analysis is outlined with the aim of mapping and assessing the behavior of the lubrication circuit.

The study of the lubrication in gearboxes is an important issue in the design of off-road machines because their reliability depends mostly on the lubrication performance, as well as the machine’s lifetime and overall energy efficiency of the transmission is strongly dependent on the lubrication system behavior. In fact the role of the lubrication system is twofold: firstly to remove the heat generated in the highly loaded rolling bearings and the gears found in the power and accessory gearboxes via heat exchangers; secondly to lubricate these parts. The trend in the development of gearbox transmissions has been towards lower consumption and higher power transmitted, consequently it is necessary to conceive more effective and efficient lubrication systems. Nonetheless the lubrication problem often relies on a trial and error approach and most available scientific literature is based on lumped element model dynamic simulation or one phase thermo-fluid dynamic simulations, overlooking the effects linked to cavitation and air inclusion.

One important phenomenon in lubrication systems is that of air suction. This can be seen in particular at high rotational speeds of shafts when the centrifugal force causes a positive pressure drop between inner lubrication pipes and outer radial conduits. In this case the air occupies part of the lubrication conduits, and since the domain is shared by the outflowing liquid phase and the air included, the monophase CFD simulation fails to predict the correct lubrication flow. If this effect is not carefully considered it could cause a lubrication unbalance among the various parts of the gearbox, creating a risk of transmission damage.

In this paper the methodology will be presented step by step until in final a complete map of operation condition is created. A preliminary analysis of the circuitry is an essential phase of the project since the tractor’s transmission is an extremely complex assembly composed by hundreds of components therefore the lubrication circuit appears as a large net of moving hydraulic connections and consumers. From this analysis a computational domain is obtained and appropriately meshed. After the pivotal choice of the proper turbulence model and boundary conditions, various runs at different rotating speeds corresponding to the different operating ranges will be performed. The result will be contextualized by commenting on the fluid dynamics phenomena involved and the influence parameters on flow rate distribution, finally evaluating the performances of the lubrication circuit, and in particular highlighting the most critical conditions in terms of speed condition and locating the most critical gearbox parts.
Nonlinear Modeling and Experimental Validation of Uni-Axial Servo-Hydraulic Shaking Table
Authors: Righettini Paolo , Strada Roberto , Valilou Shirin , Khademolama Ehsan
Published: November 2016

An effective way for the testing of a large number of systems is using single and multi-axis shaking tables. Among the possible applications, the civil engineering field stands out for the testing of structures, or part of them, both on a reduced and on a full scale. However, design a high performance controller for a servo-hydraulic shaking table is a difficult problem due to its non-linarites and large friction forces. The goal of this paper is to develop and experimentally validate a robust numerical model that simulates the acceleration behavior of a uni-axial servo-hydraulic shaking table system with considering three friction models, the LuGre model, the modified LuGre model and the new modified LuGre model. First, a full system model of servo-hydraulic system is developed based on fluid mechanical expressions and then the friction force of hydraulic cylinder is modeled and validated on the real shaking table. Data of the experiment are gathered from input command valve, and the output acceleration and position of the table. All models are simulated by using MATLAB and SIMULINK computer program. The parameters of the system and the friction models are estimated by using least square method (LSM). Finally, the comparisons of simulated results with experimental ones show that the model of the system with considering third model of the friction can predict accurately the shaking table’s behaviors.
An Efficient, High Performance and Low-Cost Energy Recovering Hydrostatic Linear Actuator Concept
Authors: Wiens Travis , Bitner Douglas
Published: November 2016

Hydrostatic or closed-circuit pump-controlled hydraulic systems are attractive due to their high energy efficiency; their lack of throttling losses and ability to recover energy onto the pump shaft have made them a common design choice in systems using rotary actuators such as ground drive transmissions. However, the natural asymmetrical flow of typical hydraulic cylinders have prevented the widespread adoption of closed-circuit systems for linear actuators. Some hydrostatic linear actuator systems have been developed, but these suffer from a large dead volume and reduced force if using a symmetrical dual rod cylinder, or increased cost and complexity if using a specialized cylinder geometry or flow balancing circuits. This paper presents a concept system which uses a pair of common single-rod hydraulic cylinders to achieve the efficiency of a pump-controlled hydrostatic system with the opportunity for energy recovery. The system’s available force is equal to a standard valve-controlled system with a greater maximum velocity. This is achieved using only commercially-available components. The paper will present an analysis of the theoretical energy recovery potential over a representative work cycle for a hydraulic excavator. It will also present a controller design analysis and experimental verification.
Guidelines for Properly Adjusting Pressure Feedback in Systems With Over-Centre Valves
Authors: Pedersen Henrik C. , Andersen Torben O. , Hansen Michael R.
Published: November 2016

Many mobile hydraulic systems are fitted with over centre valves for safety measures. However, it is well known that over centre valves in combination with pressure compensated flow control valves may lead to oscillatory and even unstable system behaviour. The traditional solution to overcome this problem is to use an over centre valve with a sufficiently low pilot ratio and/or include various damping orifices in the system. Both of these solutions are energy consuming and may decrease the control performance. An alternative approach is to use (electronic) pressure feedback — also referred to as active damping — to stabilise the system and damp pressure pulsations. This is not a new method, but the effect and adjustment of the filters is often misunderstood leading to incorrectly adjusted filters and degraded system performance. The focus of the current paper is therefore to explain and derive a set of guidelines for how to properly adjust a standard pressure feedback in system with an over centre valve when also considering model uncertainties, un-modelled dynamics and parameter variations.

The paper takes its basis in a standard cylinder drive with an inertia load, over centre valve and a pressure compensated proportional valve. Based on a linearized model of the system, the system is analysed and it is shown that there is an optimal range for both the filter frequency and gain, which are closely linked. It is furthermore shown that these both closely affect the obtainable damping and dynamic response of the system. From the analysis a set of guidelines are derived for how to properly adjust the filter coefficients and the effect of different filter adjustments are shown and commented for the example system.
Hydraulic Flow Ripple Cancellation Using the Primary Flow Source
Authors: O’Shea Colin
Published: November 2016

Flow ripple is generally considered to be a negative attribute of positive displacement units as the resulting pressure ripple can cause unsteady behavior in the overall system as well as generate significant audible noise that can spread throughout the entire hydraulic system. Passive methods of attenuating pressure ripple have included both pump design and adding compliant elements such as pulsation dampers and Helmholtz-style resonators that are often limited in their effectiveness and introduce compromises with regards to system size and response time. Active techniques have also been investigated and typically seek to employ a secondary flow source to actively cancel the flow pulsations, often with the use of feedback sensors such as pressure transducers. Some techniques using speed variation of the pump have been investigated theoretically and pointed to the limitations of the technique when applied to piston pumps of a certain size.

This paper will discuss the theory and implementation of a feed-forward motor torque control algorithm to reduce flow ripple and therefore pressure ripple by influencing the speed of a relatively-high volumetric displacement low-inertia pump through open loop control of the driving motor torque. The application under consideration is that of a gerotor pump/motor in lockstep fluid communication with a compact hydraulic actuator. The commercial application for the compact hydraulic actuators used in this study is for use as localized force sources in a fully active suspension system of sedan-sized automobiles.
Robotic Arm for Automatic Sound Intensity Measurements
Authors: Kalbfleisch Paul , Kim Taeho , Ivantysynova Monika
Published: November 2016

The characterization of the noise emitted by positive displacement machines serves as an important metric for the design of positive displacement machines and their corresponding systems. One method of characterizing the noise produced by positive displacement machines utilizes the two microphone-intensity probes at various locations surrounding the unit to approximate the total sound power generated by the machine in question.

This paper proposes a method of utilizing a robotic arm to perform automatic sound intensity measurements (ASIM). This paper will explain the various theoretical motivations and justifications for the basic design concept as well as the specific implementation.

All the necessary theoretical considerations and technical difficulties were accounted for in the successful design and manufacturing of an ASIM robot.

To highlight the usefulness of the automatic measurement procedure, three case studies was performed to evaluate the robotic ASIM’s ability to measure sound power. A total of 1086 measurement locations were taken in order for each grid study to quantify the convergence of the field non-uniformity.
A Simple and Robust Sliding Mode Velocity Observer for Moving Coil Actuators in Digital Hydraulic Valves
Authors: Noergaard Christian , Schmidt Lasse , Bech Michael M.
Published: November 2016

This paper focuses on estimating the velocity and position of fast switching digital hydraulic valves actuated by electromagnetic moving coil actuators, based on measurements of the coil current and voltage. The velocity is estimated by a simple first-order sliding mode observer architecture and the position is estimated by integrating the estimated velocity. The binary operation of digi-valves enables limiting and resetting the position estimate since the moving member is switched between the mechanical end-stops of the valve. This enables accurate tracking since drifting effects due to measurement noise and integration of errors in the velocity estimate may be circumvented. The proposed observer architecture is presented along with stability proofs and initial experimental results. To reveal the optimal observer performance, an optimization of the observer parameters is carried out. Subsequently, the found observer parameters are perturbed to assess the robustness of the observer to parameter estimation errors. The proposed observer demonstrates accurate tracking of the valve movement when using experimentally obtained data from a moving coil actuated digi-valve prototype and observer parameters estimates in the vicinity of the optimized parameter values.
Experimental and Numerical Assessment of an Axial Piston Pump’s Speed Limit
Authors: Kunkis Markus , Weber Jürgen
Published: November 2016

A high power density is a crucial requirement to axial piston pumps. It is determined by the machines’ maximum pressure and speed. At high rotational speeds, cavitation leads to the partial filling of the cylinders with gas and causes a breakdown of the delivery flowrate. A further increase of the speed limit requires a deep understanding of these effects. Since they are very hard to capture metroligically, power density has not significantly increased over the past 20 years. Recently, the steadily increasing availability of computational power has made possible the simulation, visualisation and analysis of the flow effects inside the pumps by means of computational fluid dynamics. In this paper, a criterion and a method for the precise determination of the pumps’ speed limit are presented. The description of the experimental setup is followed by flow characteristics measured at varying suction and delivery pressures. Afterwards, a CFD model of the pump is presented. It is shown how the measured flow characteristics can be reproduced in the simulation. The flow phenomena causing the speed-limiting cavitation effects are identified by a detailed analysis of the CFD results. Eventually, constructive countermeasures allowing increased rotational speeds and thereby power densities are proposed.
Towards Oscillation Reduction in Forestry Cranes
Authors: Fodor Szabolcs , Vázquez Carlos , Freidovich Leonid , Sepehri Nariman
Published: November 2016

Smooth operation of heavy-duty forestry cranes is not an easy task for the operators with the current joystick-based control method that is complex and non-intuitive. Moreover, abrupt movements of the same joysticks provoke aggressive signals that can lead to oscillatory motions in the actuators and in the entire crane. These oscillations, not only contribute to wear of the joint actuators but also can cause damage to both the operators and the environment; therefore, they must be attenuated. The proposed approach in this paper uses the popular input shaping control technique combined with a practical switching logic to deal with different frequency payload oscillations induced by the motion of the inner boom actuator of a forwarder crane. The results show a significant improvement in terms of visible oscillation reduction monitored through their appearance in the torque signal computed from pressure measurements. Experiments performed on a down-sized forestry crane verifies the effectiveness of the approach.
Direct proof of spontaneous translocation of lipid-covered hydrophobic nanoparticles through a phospholipid bilayer
Authors: Guo Yachong , Terazzi Emmanuel , Seemann Ralf , Fleury Jean Baptiste , Baulin Vladimir A.
Published: November 2016

Spontaneously translocating lipid-coated hydrophobic gold nanoparticles open doors for new biotechnology applications.
Sea ice shrinks in step with carbon emissions
Authors: Cornwall Warren
Published: November 2016

Models may underestimate the pace of ice loss because they are missing Arctic warming
Exploring pain pathophysiology in patients
Authors: Sommer Claudia
Published: November 2016

Although animal models of pain have brought invaluable information on basic processes underlying pain pathophysiology, translation to humans is a problem. This Review will summarize what information has been gained by the direct study of patients with chronic pain. The techniques discussed range from patient phenotyping using quantitative sensory testing to specialized nociceptor neurophysiology, imaging methods of peripheral nociceptors, analyses of body fluids, genetics and epigenetics, and the generation of sensory neurons from patients via inducible pluripotent stem cells.
Water strategies for the next administration
Authors: Gleick Peter H.
Published: November 2016

Water policy offers opportunity for nonpartisan agreement
Parsing reward from aversion
Authors: Beyeler Anna
Published: November 2016

Investigating the neural circuits encoding emotional valence
Building connections
Authors: Krishnaswamy Arjun
Published: November 2016

Studies in the developing retina provide insights into neural circuit assembly
Deep-sea corals feel the flow
Authors: Yokoyama Yusuke , Esat Tezer M.
Published: November 2016

Uranium isotope data from deep-water corals help to resolve conflicting results from shallow-water corals
Building bridges to regenerate axons
Authors: Williams Philip R. , He Zhigang
Published: November 2016

A secreted factor stimulates glia to mend spinal cord injury
Identification of a repressor gene involved in the regulation of NAD de novo biosynthesis in Salmonella typhimurium
Authors: Zhu N , Olivera B M , Roth J R
Published: November 2016

Mutations at the nadI locus affect expression of the first two genes of NAD synthesis, nadA and nadB, which are unlinked. Genetic data imply that the regulatory effects of nadI mutations are not due to indirect consequences of physiological alterations. Two types of mutations map in the nadI region. Common null mutations (nadI) show constitutive high-level expression of the nadB and nadA genes. Rare nadIs mutations cause constitutive low-level expression of nadB and nadA. Some nadIs mutations shut off the expression of the biosynthetic genes sufficiently to cause a nicotinic acid auxotrophy. Spontaneous revertants of auxotrophic nadIs mutants have a NadI- phenotype, including some with deletions of the nadI locus. The nadI locus encodes a repressor protein acting on the unlinked nadA and nadB genes.
Control of intracellular serine protease expression in Bacillus subtilis
Authors: Ruppen M E , Van Alstine G L , Band L
Published: November 2016

Expression of the major intracellular serine protease (ISP-1) gene of Bacillus subtilis was studied by using a translational fusion plasmid in which the isp promoter region was fused to the lacZ gene. beta-Galactosidase activity, used to measure transcription from the isp promoter, was produced immediately after the end of exponential growth, whereas intracellular protease activity was not detected until 4 h later. These results are consistent with a previous suggestion that ISP-1 initially accumulates in the cell in an enzymatically inactive form. ISP-1 activity was detected in all of the sporulation-deficient strains examined, and the amount of protease activity always corresponded to the amount of beta-galactosidase activity. These results indicate that the activation of ISP-1 is not dependent on a sporulation-specific gene product. Expression of ISP-1 is regulated by a number of mutations known to affect the expression of extracellular enzymes. In sacU(h) and sacQ(h) mutants, the expression of ISP-1 was 10-fold higher than in the wild-type strain. In catA, hpr, and scoC strains, expression of ISP was stimulated two- to threefold, whereas in sacU mutants the expression of ISP-1 was reduced to less than 10% of the wild-type level. The temporal expression and activation of ISP-1 was not affected by any of these mutations. This is the first evidence that the expression of a native intracellular protein is affected by these hyperproduction mutations.
Dicarboxylic acid transport in Bradyrhizobium japonicum: use of Rhizobium meliloti dct gene(s) to enhance nitrogen fixation
Authors: Birkenhead K , Manian S S , O'Gara F
Published: November 2016

A recombinant plasmid encoding Rhizobium meliloti sequences involved in dicarboxylic acid transport (plasmid pRK290:4:46) (E. Bolton, B. Higgisson, A. Harrington, and F. O'Gara, Arch. Microbiol. 144:142-146, 1986) was used to study the relationship between dicarboxylic acid transport and nitrogen fixation in Bradyrhizobium japonicum. The expression of the dct sequences on plasmid pRK290:4:46 in B. japonicum CJ1 resulted in increased growth rates in media containing dicarboxylic acids as the sole source of carbon. In addition, strain CJ1(pRK290:4:46) exhibited enhanced succinate uptake activity when grown on dicarboxylic acids under aerobic conditions. Under free-living nitrogen-fixing conditions, strain CJ1(pRK290:4:46) exhibited higher nitrogenase (acetylene reduction) activity compared with that of the wild-type strain. This increase in nitrogenase activity also correlated with an enhanced dicarboxylic acid uptake rate under these microaerobic conditions. The regulation of dicarboxylic acid transport by factors such as metabolic inhibitors and the presence of additional carbon sources was similar in both the wild-type and the engineered strains. The implications of increasing nitrogenase activity through alterations in the dicarboxylic acid transport system are discussed.
Efficient expression of the yeast metallothionein gene in Escherichia coli
Authors: Berka T , Shatzman A , Zimmerman J , Strickler J , Rosenberg M
Published: November 2016

The yeast metallothionein gene CUP1 was cloned into a bacterial expression system to achieve efficient, controlled expression of the stable, unprocessed protein product. The Escherichia coli-synthesized yeast metallothionein bound copper, cadmium, and zinc, indicating that the protein was functional. Furthermore, E. coli cells expressing CUP1 acquired a new, inducible ability to selectively sequester heavy metal ions from the growth medium.
Evidence for methyl group transfer between the methyl-accepting chemotaxis proteins in Bacillus subtilis
Authors: Bedale W A , Nettleton D O , Sopata C S , Thoelke M S , Ordal G W
Published: November 2016

We present evidence for methyl (as methyl or methoxy) transfer from the methyl-accepting chemotaxis proteins H1 and possibly H3 of Bacillus subtilis to the methyl-accepting chemotaxis protein H2. This methyl transfer, which has been observed in vitro (D. J. Goldman and G. W. Ordal, Biochemistry 23:2600-2606, 1984), was strongly stimulated by the chemoattractant aspartate and thus may play an important role in the sensory processing system of this organism. Although radiolabeling of H1 and H3 began at once after the addition of [3H]methionine, radiolabeling of H2 showed a lag. Furthermore, the addition of excess nonradioactive methionine caused immediate exponential delabeling of H1 and H3 while labeling of H2 continued to increase. Methylation of H2 required the chemotactic methyltransferase, probably to first methylate H1 and H3. Aspartate caused increased labeling of H2 and strongly decreased labeling of H1 and H3 after the addition of nonradioactive methionine. Without the addition of nonradioactive methionine, aspartate caused demethylation of H1 and to a lesser extent H3, with an approximately equal increase of methylation of H2.
Genetic organization of the bacterial conjugative transposon Tn916
Authors: Senghas E , Jones J M , Yamamoto M , Gawron-Burke C , Clewell D B
Published: November 2016

Tn916, which encodes resistance to tetracycline, is a 16.4-kilobase conjugative transposon originally identified on the chromosome of Streptococcus faecalis DS16. The transposon has been cloned in Escherichia coli on plasmid vectors, where it expresses tetracycline resistance; it can be reintroduced into S. faecalis via protoplast transformation. We have used a lambda::Tn5 bacteriophage delivery system to introduce Tn5 into numerous sites within Tn916. The Tn5 insertions had various effects on the behavior of Tn916. Some insertions eliminated conjugative transposition but not intracellular transposition, and others eliminated an excision step believed to be essential for both types of transposition. A few inserts had no effect on transposon behavior. Functions were mapped to specific regions on the transposon.
Isolation, sequence analysis, and transcriptional studies of the flavodoxin gene from Anacystis nidulans R2
Authors: Laudenbach D E , Reith M E , Straus N A
Published: November 2016

The nonheme, iron-sulfur protein ferredoxin is the terminal constituent of the photosynthetic electron transport chain. Under conditions of iron stress, many cyanobacteria and eucaryotic algae replace ferredoxin with the flavoprotein flavodoxin. The gene for flavodoxin was cloned from the cyanobacterium Anacystis nidulans R2 by using three mixed oligonucleotide probes derived from the partial Synechococcus sp. strain PCC 6301 amino acid sequence. Nucleotide sequence analysis revealed a 513-base-pair open reading frame with a deduced amino acid sequence having homology to other long-chain flavodoxins. Assuming proteolytic cleavage of the initial methionine residue, the molecular weight of the A. nidulans R2 flavodoxin is 18,609. Southern blot hybridization under conditions of reduced stringency detected only one copy of the flavodoxin sequence in the A. nidulans R2 genome. Northern (RNA) blot hybridization analyses by using cloned flavodoxin gene probes indicated that no transcripts are detectable under conditions of iron saturation. However, under iron-deficient growth conditions the flavodoxin gene appeared to be transcribed as part of a larger operon. The operon yielded at least three transcripts. The first was of approximately 1,100 bases (designated RNA 1) and terminated immediately upstream from the 5' end of the flavodoxin open reading frame. A second, less abundant transcript of approximately 1,900 bases (designated RNA 2) encoded all of RNA 1 as well as the flavodoxin polypeptide. Analysis indicated that both transcripts initiate in close proximity to each other. A third, minor transcript of approximately 1,100 bases (designated RNA 3) was detectable downstream of the flavodoxin gene sequence. Addition of iron-stressed A. nidulans R2 cells resulted in almost total loss of detectable mRNA transcripts within 60 min of the addition. The ferredoxin gene transcript has previously been characterized as a monocistronic message of approximately 430 bases (M. E. Reith, D. E. Laudenbach, and N. A. Straus, J. Bacteriol. 168: 1319-1324, 1986). Here we show that the ferredoxin message is detectable under all iron regimes tested is quantitatively unaffected by decreases in iron availability to the cells.
Isolation and characterization of an Escherichia coli K-12 mutant deficient in glutaredoxin
Authors: Kren B , Parsell D , Fuchs J A
Published: November 2016

Mutants of Escherichia coli K-12 deficient in glutaredoxin were isolated and partially characterized. The mutants have detectable but significantly reduced glutaredoxin activity in assays of whole cells made permeable with ether as well as in assays of crude extracts coupled to ribonucleotide reductase. In vivo, the mutants appear to be deficient in both sulfate and ribonucleotide reduction, suggesting that in vivo glutaredoxin is the preferred cofactor for ribonucleotide reductase and adenosine 3'-phosphate 5'-phosphosulfate reductase. Complementation of the mutant phenotype by transformants was used to clone the wild-type glutaredoxin allele. The transformants had a high level of glutaredoxin activity and contained a plasmid with an insert that had a restriction endonuclease pattern identical to that predicted by the DNA sequence for glutaredoxin determined by Hoog et al. (J.-O. Hoog, H. von Bahr-Lindstrom, H. Jornvall, and A. Holmgren, Gene 43:13-21, 1986).
Catabolism of aromatic biogenic amines by Pseudomonas aeruginosa PAO1 via meta cleavage of homoprotocatechuic acid
Authors: Cuskey S M , Olsen R H
Published: November 2016

Pseudomonas aeruginosa PAO1 catabolized the aromatic amines tyramine and octopamine through 4-hydroxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid (HPA). meta ring cleavage was mediated by 3,4-dihydroxyphenylacetate 2,3-dioxygenase (HPADO), producing 2-hydroxy-5-carboxymethylmuconic semialdehyde (MSA). An NAD-dependent dehydrogenase caused the disappearance of the yellow MSA product, probably forming 2-hydroxy-5-carboxymethylmuconic acid. Induction studies with extracts from mutant cells indicated that the inducer of HPADO was HPA and/or MSA. Strains PAO1.221 (tynC1) and PAO1.303 (tynD1) have chromosomal mutations causing a deficiency in the activity necessary for conversion of 4-hydroxyphenylacetic acid to HPA. Genetic analyses showed that the mutations were in different loci. Strains PAO1.197 (tynE1) and PAO1.185 (tynF1) are deficient in HPADO and the NAD-dependent dehydrogenase, respectively. Plasmid pRO1853 was constructed by cloning approximately 7.3 kilobases of PAO1 chromosomal DNA into the BamHI site of the vector plasmid pRO1614. This recombinant plasmid complemented the tynD1, tynE1, and tynF1 mutations. A putative repressor-binding site involved in the regulation of HPADO synthesis was observed for a subcloned fragment of pRO1853. This recombinant plasmid, pRO1863, failed to complement tynE1 or tynF1 but still complemented tynD1. Another construct, pRO1887, contained 9.2 kilobases of PAO1 chromosomal DNA inserted in the PstI site of the vector pRO1727. Plasmid pRO1887 complemented only the tynC1 mutation. Mapping experiments performed with the chromosome-mobilizing plasmid R68.45 located the mutations described above in a cluster at about 35 to 40 min of the PAO1 chromosome map. The mutations were linked to the proA, thr-48, lys-9015, argF10, and argG markers.
Sequential regulation of developmental events during polar morphogenesis in Caulobacter crescentus: assembly of pili on swarmer cells requires cell separation
Authors: Sommer J M , Newton A
Published: November 2016

Pili, along with the flagellum and DNA bacteriophage receptors, are structural markers for polar morphogenesis in Caulobacter crescentus. Pili act as primary receptors for a number of small, C. crescentus-specific DNA and RNA bacteriophages, and the timing of pilus-dependent adsorption of bacteriophage phiCb5 in synchronized cell populations has led to the general conclusion that pili are formed coordinately with the flagellum and other polar surface structures in the predivisional cell. The use of rotary platinum shadow casting and electron microscopy as a direct assay for formation of flagella and pili in synchronous cell cultures now shows, however, that when expressed as fractions of the swarmer cell cycle, flagella are assembled on the predivisional cells at approximately 0.8 and that pili are assembled on the new swarmer cells at approximately 0.1 of the next cell cycle. Adsorption of pilus-specific bacteriophage phiCb5 prevented the loss of pili from swarmer cells during development, which suggests that these structures are retracted at the time of stalk formation. Examination of temperature-sensitive cell division mutants showed that the assembly of pili depends on completion of cell separation. These results indicate that the stage-specific events required for polar morphogenesis in C. crescentus occur sequentially, rather than coordinately in the cell cycle, and that the timing of these events reflects the order of underlying cell cycle steps.
Rate and topography of cell wall synthesis during the division cycle of Salmonella typhimurium
Authors: Cooper S
Published: November 2016

The rates of synthesis of peptidoglycan and protein during the division cycle of Salmonella typhimurium have been measured by using the membrane elution technique and differentially labeled diaminopimelic acid and leucine. The cells were labeled during unperturbed exponential growth and then bound to a nitrocellulose membrane by filtration. Newborn cells were eluted from the membrane with fresh medium. The radioactivity in the newborn cells in successive fractions was determined. As the cells are eluted from the membrane as a function of their cell cycle age at the time of labeling, the rate of incorporation of the different radioactive compounds as a function of cell cycle age can be determined. During the first part of the division cycle, the ratio of the rates of protein and peptidoglycan synthesis was constant. During the latter part of the division cycle, there was an increase in the rate of peptidoglycan synthesis relative to the rate of protein synthesis. These results support a simple, bipartite model of cell surface increase in rod-shaped cells. Before the start of constriction, the cell surface increased only by cylindrical extension. After cell constriction started, the cell surface increased by both cylinder and pole growth. The increase in surface area was partitioned between the cylinder and the pole so that the volume of the cell increased exponentially. No variation in cell density occurred because the increase in surface allowed a continuous exponential increase in cell volume that accommodated the exponential increase in cell mass. Protein was synthesized exponentially during the division cycle. The rate of cell surface increase was described by a complex equation which is neither linear nor exponential.
Variation in precursor pool size during the division cycle of Escherichia coli: further evidence for linear cell growth
Authors: Kubitschek H E , Pai S R
Published: November 2016

The magnitudes of several pools of radioactively labeled precursors for RNA and protein synthesis were determined as a function of cell age during the division cycle of Escherichia coli 15 THU. Uracil, histidine, and methionine pools increased from low initial values for cells at birth to maxima during midcycle and then subsided again. These pools were small or nonexistent at the beginning and the end of the cycle, and their average values during the cycle were less than 4% of the total cellular radioactivity. The results are consistent with a linear pattern of growth for cells during the division cycle and provide strong evidence against exponential or bilinear growth of E. coli cells.
ATP-liganded form of aspartate transcarbamoylase, the logical regulatory target for allosteric control in divergent bacterial systems
Authors: Wild J R , Johnson J L , Loughrey S J
Published: November 2016

In Escherichia coli, the mechanism for regulatory control of aspartate transcarbamoylase is clear; CTP allosterically inhibits catalysis in direct competition with ATP. However, both CTP and ATP may be activators or may have no effect on aspartate transcarbamoylases from other enteric bacteria. A common regulatory logic observed was that the ATP-activated enzymes were rendered less active as the result of competition with CTP, regardless of the independent effects.
Direct repeats flanking the Bacteroides transposon Tn4351 are insertion sequence elements
Authors: Hwa V , Shoemaker N B , Salyers A A
Published: November 2016

The clindamycin-erythromycin resistance (Ccr Emr) region of the Bacteroides transposon Tn4351 is flanked by direct repeats. This study showed that the direct repeats are insertion sequence (IS) elements. Although both IS elements can mediate transfer of the chloramphenicol (Cmr) marker on pBR328 by cointegrate formation with the conjugal IncW plasmid R388, IS4351R-mediated transfer of Cmr occurred at a consistently lower frequency than did the transfer mediated by IS4351L. Analysis of plasmids from the resultant transconjugants revealed IS-mediated activities such as deletions, tandem duplication of IS4351L, and excision of IS4351R.
Flagellin domain that affects H antigenicity of Escherichia coli K-12
Authors: Kuwajima G
Published: November 2016

Escherichia coli K-12 mutants with altered flagellum antigenicity were isolated by introducing random deletions into the flagellin gene. The deletions were identified in the central region of the gene. It is suggested that this region corresponds to the flagellin domain molecule which affects flagellum antigenicity.
Mode of action of the staphylococcinlike peptide Pep 5: voltage-dependent depolarization of bacterial and artificial membranes
Authors: Kordel M , Benz R , Sahl H G
Published: November 2016

The cationic staphylococcinlike peptide Pep 5 is shown to depolarize bacterial and planar lipid membranes in a voltage-dependent manner. An artificial valinomycin-induced potassium diffusion potential across the cytoplasmic membrane of Staphylococcus cohnii 22 was sufficient to promote Pep 5 action. Thus, evidence is provided that a membrane potential of sufficient magnitude is the only prerequisite for Pep 5 activity. The voltage dependence was elucidated by macroscopic conductance measurements with black lipid membranes. A threshold potential of about -90 to -100 mV, which was deduced from experiments with bacterial cells, could be confirmed. Single pores were resolved which often occur as short-lived bursts and fluctuate among different conductance levels. Pore diameters were calculated ranging from 0.1 to 1 nm. Succinylation of the lysine residues of Pep 5 resulted in prolonged pore lifetimes and maintenance of distinct conductance levels. However, the succinylated peptide required a higher threshold potential, approximately -150 mV, than the native peptide, which is probably the reason for the reduced activity of the modified peptide against intact gram-positive bacteria.
Nucleotide sequence and expression of the aceK gene coding for isocitrate dehydrogenase kinase/phosphatase in Escherichia coli
Authors: Cortay J C , Bleicher F , Rieul C , Reeves H C , Cozzone A J
Published: November 2016

The flow of isocitrate through the glyoxylate bypass in Escherichia coli is regulated via the phosphorylation-dephosphorylation of isocitrate dehydrogenase mediated by a bifunctional enzyme: isocitrate dehydrogenase kinase/phosphatase. The aceK gene coding for this enzyme is part of the polycistronic ace operon, which also includes the aceB and aceA genes coding, respectively, for malate synthase and isocitrate lyase, the two glyoxylate bypass enzymes. The complete nucleotide sequence of a 2,214-base-pair DNA fragment containing the aceK gene and its 5' flanking region has been determined. In vivo experiments based on gene expression in a minicell system and protein fusion with beta-galactosidase, as well as in vitro assays with a plasmid-directed transcription-translation coupled system, have shown that the aceK gene extends over 1,731 nucleotides encoding a 66,528-dalton protein. The 5' flanking region presents an unusual intercistronic structural pattern consisting of two consecutive long dyad symmetries, almost identical in sequence, which can yield very stable stem-loop units. These structures are probably responsible for the drastic downshifting in expression observed in acetate-grown bacteria between the aceK gene and the aceA gene located immediately upstream in the ace operon.
Complete physical map of the rfb gene cluster encoding biosynthetic enzymes for the O antigen of Salmonella typhimurium LT2
Authors: Brahmbhatt H N , Wyk P , Quigley N B , Reeves P R
Published: November 2016

Biosynthesis of the Salmonella typhimurium LT2 O antigen is encoded by genes which map in the rfb cluster. The cloning and restriction enzyme analysis of part of this cluster have been described previously (H. N. Brahmbhatt, N. B. Quigley, and P. R. Reeves, Mol. Gen. Genet. 203:172-176, 1986). The entire rfb gene cluster has now been cloned, and a detailed restriction enzyme map has been constructed which has enabled us to map the approximate positions of individual rfb genes.