Improvement of antibiotic activity of Xenorhabdus bovienii by medium optimization using response surface methodology

<p>Abstract</p> <p>Background</p> <p>The production of secondary metabolites with antibiotic properties is a common characteristic to entomopathogenic bacteria <it>Xenorhabdus</it> spp. These metabolites not only have diverse chemical structures but also have a wide range of bioactivities with medicinal and agricultural interests such as antibiotic, antimycotic and insecticidal, nematicidal and antiulcer, antineoplastic and antiviral. It has been known that cultivation parameters are critical to the secondary metabolites produced by microorganisms. Even small changes in the culture medium may not only impact the quantity of certain compounds but also the general metabolic profile of microorganisms. Manipulating nutritional or environmental factors can promote the biosynthesis of secondary metabolites and thus facilitate the discovery of new natural products. This work was conducted to evaluate the influence of nutrition on the antibiotic production of <it>X. bovienii</it> YL002 and to optimize the medium to maximize its antibiotic production.</p> <p>Results</p> <p>Nutrition has high influence on the antibiotic production of <it>X. bovienii</it> YL002. Glycerol and soytone were identified as the best carbon and nitrogen sources that significantly affected the antibiotic production using one-factor-at-a-time approach. Response surface methodology (RSM) was applied to optimize the medium constituents (glycerol, soytone and minerals) for the antibiotic production of <it>X. bovienii</it> YL002. Higher antibiotic activity (337.5 U/mL) was obtained after optimization. The optimal levels of medium components were (g/L): glycerol 6.90, soytone 25.17, MgSO₄·7H₂O 1.57, (NH₄)₂SO₄ 2.55, KH₂PO₄ 0.87, K₂HPO₄ 1.11 and Na₂SO₄ 1.81. An overall of 37.8% increase in the antibiotic activity of <it>X. bovienii</it> YL002 was obtained compared with that of the original medium.</p> <p>Conclusions</p> <p>To the best of our knowledge, there are no reports on antibiotic production of <it>X. boviebii</it> by medium optimization using RSM. The results strongly support the use of RSM for medium optimization. The optimized medium not only resulted in a 37.8% increase of antibiotic activity, but also reduced the numbers of experiments. The chosen method of medium optimization was efficient, simple and less time consuming. This work will be useful for the development of <it>X. bovienii</it> cultivation process for efficient antibiotic production on a large scale, and for the development of more advanced control strategies on plant diseases.</p

Stress tunable magnetic stripe domains in flexible Fe81Ga19 films

In this paper, we propose an approach that combines in situ mechanical-stress measurement and magnetic force microscopy (MFM) imaging and enable manipulation of the spin configuration of flexible films by tailoring the stress-induced anisotropy. We demonstrate that the stress-induced anisotropy can effectively rotate stripe domains. We see that, without the application of the magnetic field, the stripe domains tend to align parallel (perpendicular) to the direction of tensile (compressive) stress. The expansion (shrinkage) of flux-closure cap domains in response to applied tensile (compressive) stress, changes the out-of-plane stray field and the profile in the MFM image. The experimental results have been reproduced very well by micromagnetic simulations assuming a stress-induced anisotropy. Furthermore, we studied the evolution of stripe domains in the film with compressive stress against a decreasing magnetic field. It is indicated that in-plane mechanical stress can effectively convert stripe domains with Bloch walls to those with Neel walls. The observed stress-modulation of magnetic stripe domains may find application in microwave absorbers and flexible electronics

Photoexcited terahertz conductivity dynamics of graphene tuned by oxygen-adsorption

By using optical pump-terahertz (THz) probe spectroscopy, the photoexcited terahertz conductivity dynamics of chemical vapor deposition grown graphene is investigated in different atmospheric environments. It is shown that the Fermi energy of doped graphene is engineered by oxygen adsorption and desorption, which is probed by transient THz conductivity measurement. We show that the ultrafast energy relaxation processes depend on Fermi energy (changed by environmental gas) and the density of excited carriers (changed by photo-excitation fluence). The rise process of the negative conductivity dynamics becomes less efficient upon decreasing the Fermi energy and/or increasing the pump fluence. All findings show that the Fermi energy of graphene engineered by environmental gas allows us to tune the ultrafast energy relaxation pathways in photoexcited graphene

Three-dimensional numerical simulations on the effect of ignition timing on combustion characteristics, nitrogen oxides emissions, and energy loss of a hydrogen fuelled opposed rotary piston engine over wide open throttle conditions

Opposed rotary piston (ORP) engines have advantages of high power density, few moving parts, and smooth operations, which makes ORP engines as potential power sources for hybrid vehicles and range extended electric vehicles. Ignition timing significantly affects the performance of spark ignition engines including fuel economy and emission factors. In this paper, the effect of ignition timing on the engine performance was investigated using a three-dimensional numerical simulation method. The results indicated that crank angle corresponding to the peak in-cylinder pressure over the ignition timing of −8.2° crank angle (CA) was advanced compared with other cases having earlier ignition timing; however, the crank angle of peak heat release rates were retarded. Start of combustion was delayed by retarding the ignition timing and increasing engine speed; combustion duration over the ignition timing of −18.9° CA ~ −11.1° CA changed slightly for individual engine speed. Indicated specific fuel consumption (ISFC), being hardly dependent on the ignition timing, was less than 74 g/(kW·h) over the ignition timing of −17.3° CA ~ −11.1° CA, where indicated thermal efficiency was approximately 41%, 39% and 35% for 1000 RPM, 3000 RPM and 5000 RPM respectively. When ignition timing was later than −11.1° CA, ISFC and indicated thermal efficiency were deteriorated seriously. Nitrogen oxides (NOx) emission factors increased with engine speed over early ignition timing; however, they were inverse for late ignition cases. Higher engine speed and retarded ignition timing led to higher percentage of exhaust energy in fuel chemical energy

Numerical investigations of an opposed rotary piston expander for the purpose of the applications to a small-scale Rankine cycle

Requirements of recycling low temperature waste heat energy from internal combustion engines drive the developments of excellent performance expanders with high compactness which significantly affects the applications of waste heat recovery systems to on-road vehicles. In the present study, an opposed rotary piston expander was proposed for the practical utilisations on a small-scale Organic Rankine Cycle (ORC) system, aiming at recycling the waste heat energy from internal combustion engines of on-road vehicles. The opposed rotary piston expander had a cyclic period of 180° crank angle (CA), four intake ports and two discharge ports. In order to investigate the expander performance, 3D numerical simulations were conducted under various scenarios whose boundary conditions were among the frequently reported thermodynamic states in ORC systems; additionally, these scenarios were around the design operation point of the expander. Intake and discharge characteristics, in-cylinder pressure evolutions, in-cylinder fluid flow, and P-V diagrams were analysed; further, volumetric efficiency, power output and adiabatic efficiency were calculated using the simulation results, and were compared to various types of expanders. Each two opposed cylinders had the same evolutions of cylinder volume, fluid mass, in-cylinder pressure, and temperature during operation. Maximum fluid flow rate in the intake process increased with intake pressure and rotation speed; in addition, the in-cylinder pressure reached the maximum value in a short time after the intake ports opened. However, high rotation speed also led to a drop of in-cylinder pressure (expansion process), volumetric efficiency, and adiabatic efficiency compared to low speed condition

Preliminary Investigations of an Opposed Rotary Piston Compressor for the Air Feeding of a Polymer Electrolyte Membrane Fuel Cell System

Automotive polymer electrolyte membrane fuel cell systems are attracting much attention, driven by the requirements of low automotive exhaust emissions and energy consumption. A polymer electrolyte membrane fuel cell system provides opportunities for the developments in different types of air compressors. This paper proposed an opposed rotary piston compressor, which had the merits of more compact structures, less movement components, and a high pressure ratio, meeting the requirements of polymer electrolyte membrane fuel cell systems. Preliminary performance evaluations of the opposed rotary piston compressor were conducted under various scenarios. This will make a foundation for optimizations of outlet pipe layouts of the compressor. A three-dimensional numerical simulation approach was used; further, in-cylinder pressure evolutions, fluid mass flow rates, and P–V diagrams were analyzed. It indicated that the cyclic period of the opposed rotary piston compressor was half of reciprocating piston compressors. The specific mass flow rate of the compressor is in the range of 0.094–0.113 kg·(s·L)−1 for the given scenarios. Outlet ports 1 and 2 dominated the mass flow in the discharge process under scenarios 1, 3, and 4. In-cylinder pressure profiles show multipeaks for all of these scenarios. In-cylinder pressure increased rapidly in the compression process and part of the discharge process, which led to high energy consumption and low adiabatic efficiency. The maximum adiabatic efficiency is approximately 43.96% among the given scenarios

Numerical simulation on lean-burn characteristics of a naturally aspirated opposed rotary piston engine fuelled with hydrogen at wide open throttle conditions

Opposed rotary piston engines are characterized by high power density, which makes them as an ideal power source for hybrid vehicles and range extended electric vehicles. Hydrogen applications can fully exhibit the merits of opposed rotary piston engines, and achieve zero carbon dioxide emissions; however, the applications seriously worsen the nitrogen oxides emissions. In this investigation, lean-burn was adopted to achieve low nitrogen oxides emissions using a three dimensional numerical simulation approach. The results indicated that engine speed of 3000 r/min presented the highest in-cylinder pressure during combustion among the given scenarios, and the pressure over 3000 r/min depended more on the equivalence ratio than that of 1000 r/min and 2000 r/min. Heat release rates were very sensitive to low equivalence ratio. Combustion duration over the equivalence ratio of 0.8 was the shortest among 1000 r/min cases; however, it decreased with equivalence ratio for 2000 r/min and 3000 r/min. Heat loss rates through cylinder walls increased significantly with engine speed, meanwhile they were more dependent on the equivalence ratio over higher engine speed. Maximum nitrogen monoxide formation rates over 3000 r/min occurred slightly earlier than those of 1000 r/min and 2000 r/min. Equivalence ratio of 0.8 showed the highest indicated thermal efficiency over corresponding engine speed, and nitrogen dioxide emission factors were quite low over the equivalence ratio of 0.7 for the given engine speed.[Display omitted]•Start of hydrogen combustion was retarded with the increase of equivalence ratio.•3000 RPM presented the highest in-cylinder temperature and combustion efficiency.•Indicated thermal efficiency had the highest value over the equivalence ratio of 0.8.•Heat loss through cylinder walls depended on the engine speed and equivalence ratio.•NO emission factor was much low over the equivalence ratio of 0.7

Thermodynamics of quasi-2D electron gas at BFO/Si interface probed with THz time-domain spectroscopy

An interface is constructed based on a bismuth ferrite oxide (BFO) thin film and p-type silicon, and the temperature dependence of the interface properties has been studied systematically using terahertz time-domain spectroscopy. The BFO/Si interface exhibits quasi-two-dimension electron gas (2DEG) transport in the temperature range of 80 to 140 K: the electrons at the interface possess large electron mobility (∼10 6 cm 2 /V s) and long scattering time (∼100 ps). As the temperature is higher than 140 K, an abrupt decrease in THz interface conductivity is observed due to the breakdown of the 2D EG induced by the surface phase transition in the BFO thin film. Our result reveals that the interface formed between BFO and Si provides a special platform for designing and fabricating THz photonic devices