Sergey Golubev

Oxidoreductase activity of sorghum root exudates in a phenanthrene-contaminated environment.

The effect of the polycyclic aromatic hydrocarbon (PAH) phenanthrene on the enzymatic activity of root exudates of the phytoremediating plant Sorghum bicolor (L.) Moench was studied. Analysis of sorghum root exudates allowed us to reveal the activities of oxidase, peroxidase, and tyrosinase. The activities of these enzymes were progressive as the soil phenanthrene concentration increased. Using lyophilized samples, we found that as a result of the enzymatic activity of the root exudates, some of the PAHs and products of PAH degradation were oxidized in the reaction mixture supplemented with the mediating agents (ABTS or DL-DOPA) but that no oxidation was observed in the reaction mixtures without the mediators. The revealed enzymatic activity of the sorghum root exudates may indicate the involvement of the root-released oxidoreductases in rhizospheric degradation of PAHs and/or their derivatives. In addition, from the data obtained, the coupling of plant and microbial metabolisms of PAHs in the rhizosphere may be surmised.

High current proton beams production at Simple Mirror Ion Source 37

This paper presents the latest results of high current proton beam production at Simple Mirror Ion Source (SMIS) 37 facility at the Institute of Applied Physics (IAP RAS). In this experimental setup, the plasma is created and the electrons are heated by 37.5 GHz gyrotron radiation with power up to 100 kW in a simple mirror trap fulfilling the ECR condition. Latest experiments at SMIS 37 were performed using a single-aperture two-electrode extraction system. Proton beams with currents up to 450 mA at high voltages below 45 kV were obtained. The maximum beam current density was measured to be 600 mA/cm(2). A possibility of further improvement through the development of an advanced extraction system is discussed.

Rhizosphere indole-3-acetic acid as a mediator in the Sorghum bicolor-phenanthrene-Sinorhizobium meliloti interactions.

We studied a model system consisting of Sorghum bicolor, phenanthrene, and an auxin-producing polycyclic aromatic hydrocarbon-degrading Sinorhizobium meliloti strain to clarify whether rhizosphere indole-3-acetic acid (IAA) takes part in the plant-pollutant-bacteria interactions. Phenanthrene and S. meliloti treatments of sorghum contributed to a decrease in the rhizosphere IAA concentration and to phytohormone accumulation, respectively. Regression analysis showed significant correlations between alteration in root-zone IAA content and alterations in the root-surface area, exudation, and rhizosphere effects for culturable heterotrophic bacteria, the S. meliloti strain, and other phenanthrene degraders. According to the data obtained, phenanthrene degraders get an advantage over nondegradative rhizobacteria from IAA for rhizosphere colonization. An IAA-dependent increase in the root-surface area leads to improved sorghum growth under pollutant stress. The carbon flux from the roots is corrected by the auxin because of its influence on the exuding-surface area and on the intensity of secretion by the root cells. On the other hand, the rhizosphere IAA pool may be plant-regulated by means of alteration in carboxylate exudation and its influence on bacterial auxin production. A scenario for the IAA-mediated S. bicolor-phenanthrene-S. meliloti interactions is proposed.

New progress of high current gasdynamic ion source (invited)

The experimental and theoretical research carried out at the Institute of Applied Physics resulted in development of a new type of electron cyclotron resonance ion sources (ECRISs)-the gasdynamic ECRIS. The gasdynamic ECRIS features a confinement mechanism in a magnetic trap that is different from Gellers ECRIS confinement, i.e., the quasi-gasdynamic one similar to that in fusion mirror traps. Experimental studies of gasdynamic ECRIS were performed at Simple Mirror Ion Source (SMIS) 37 facility. The plasma was created by 37.5 and 75 GHz gyrotron radiation with power up to 100 kW. High frequency microwaves allowed to create and sustain plasma with significant density (up to 8 × 10(13) cm(-3)) and to maintain the main advantages of conventional ECRIS such as high ionization degree and low ion energy. Reaching such high plasma density relies on the fact that the critical density grows with the microwave frequency squared. High microwave power provided the average electron energy on a level of 50-300 eV enough for efficient ionization even at neutral gas pressure range of 10(-4)-10(-3) mbar. Gasdynamic ECRIS has demonstrated a good performance producing high current (100-300 mA) multi-charged ion beams with moderate average charge (Z = 4-5 for argon). Gasdynamic ECRIS has appeared to be especially effective in low emittance hydrogen and deuterium beams formation. Proton beams with current up to 500 emA and RMS emittance below 0.07 π ⋅ mm ⋅ mrad have been demonstrated in recent experiments.

The coupling of the plant and microbial catabolisms of phenanthrene in the rhizosphere of Medicago sativa.

We studied the catabolism of the polycyclic aromatic hydrocarbon phenanthrene by four rhizobacterial strains and the possibility of enzymatic oxidation of this compound and its microbial metabolites by the root exudates of alfalfa (Medicago sativa L.) in order to detect the possible coupling of the plant and microbial metabolisms under the rhizospheric degradation of the organic pollutant. A comparative study of phenanthrene degradation pathways in the PAH-degrading rhizobacteria Ensifer meliloti, Pseudomonas kunmingensis, Rhizobium petrolearium, and Stenotrophomonas sp. allowed us to identify the key metabolites from the microbial transformation of phenanthrene, including 9,10-phenanthrenequinone, 2-carboxybenzaldehyde, and 1-hydroxy-2-naphthoic, salicylic, and o-phthalic acids. Sterile alfalfa plants were grown in the presence and absence of phenanthrene (0.03 g kg(-1)) in quartz sand under controlled environmental conditions to obtain plant root exudates. The root exudates were collected, concentrated by ultrafiltration, and the activity of oxidoreductases was detected spectrophotometrically by the oxidation rate for various substrates. The most marked activity was that of peroxidase, whereas the presence of oxidase and tyrosinase was detected on the verge of the assay sensitivity. Using alfalfa root exudates as a crude enzyme preparation, we found that in the presence of the synthetic mediator, the plant peroxidase could oxidize phenanthrene and its microbial metabolites. The results indicate the possibility of active participation of plants in the rhizospheric degradation of polycyclic aromatic hydrocarbons and their microbial metabolites, which makes it possible to speak about the coupling of the plant and microbial catabolisms of these contaminants in the rhizosphere.

Biochemical and physiological peculiarities of the interactions between Sinorhizobium meliloti and Sorghum bicolor in the presence of phenanthrene

The effect of phenanthrene, a polycyclic aromatic hydrocarbon (PAH) at concentrations of 0, 10, and 100 mg/kg and the bacterium Sinorhizobium meliloti P221 on root exudation of Sorghum bicolor L. Moench was studied in laboratory vegetative experiments. Inoculation of the bacterium promoted plant resistance to the pollutant stress and increased their acclimation rate and biomass formation. The ability of this microorganism to produce a phytohormone, indolyl-3-acetic acid, and to degrade phenanthrene, resulted in morphological changes of the plant root system and in the changed intensity of root exudation. In root exudates of sorghum, enzyme activities towards the metabolites formed during microbial degradation of PAH were revealed, which is indicative of a direct involvement of plants in PAH degradation in the rhizosphere as well as of the coupled plant-microbial metabolism in the course of xenobiotic degradation in the root zone. In phenanthrene-contaminated soil, sorghum was found to support selectively the development of the S. meliloti P221 population.

High yield neutron generator based on a high-current gasdynamic electron cyclotron resonance ion source

In present paper, an approach for high yield compact D-D neutron generator based on a high current gasdynamic electron cyclotron resonance ion source is suggested. Results on dense pulsed deuteron beam production with current up to 500 mA and current density up to 750 mA/cm2 are demonstrated. Neutron yield from D2O and TiD2 targets was measured in case of its bombardment by pulsed 300 mA D+ beam with 45 keV energy. Neutron yield density at target surface of 109 s−1 cm−2 was detected with a system of two 3He proportional counters. Estimations based on obtained experimental results show that neutron yield from a high quality TiD2 target bombarded by D+ beam demonstrated in present work accelerated to 100 keV could reach 6 × 1010 s−1 cm−2. It is discussed that compact neutron generator with such characteristics could be perspective for a number of applications like boron neutron capture therapy, security systems based on neutron scanning, and neutronography.

First experiments with gasdynamic ion source in CW mode

A new type of ECR ion source-a gasdynamic ECR ion source-has been recently developed at the Institute of Applied Physics. The main advantages of such device are extremely high ion beam current with a current density up to 600-700 emA/cm(2) in combination with low emittance, i.e., normalized RMS emittance below 0.1 π mm mrad. Previous investigations were carried out in pulsed operation with 37.5 or 75 GHz gyrotron radiation with power up to 100 kW at SMIS 37 experimental facility. The present work demonstrates the first experience of operating the gasdynamic ECR ion source in CW mode. A test bench of SMIS 24 facility has been developed at IAP RAS. 24 GHz radiation of CW gyrotron was used for plasma heating in a magnetic trap with simple mirror configuration. Initial studies of plasma parameters were performed. Ion beams with pulsed and CW high voltage were successfully extracted from the CW discharge. Obtained experimental results demonstrate that all advantages of the gasdynamic source can be realized also in CW operation.

Monocrystalline InN Films Grown at High Rate by Organometallic Vapor Phase Epitaxy with Nitrogen Plasma Activation Supported by Gyrotron Radiation

InN hexagonal monocrystalline films were grown on yttria-stabilized zirconia (YSZ) (111) and Al2O3(0001) by the organometallic vapor phase epitaxy method with nitrogen activation in the electron cyclotron resonance discharge, supported by gyrotron radiation. The film growth rate reached 10 µm/h. In this paper, we present data on the morphology, structure, and photoluminescence properties of the grown films.

Indium Nitride Film Growth by Metal Organic Chemical Vapor Deposition with Nitrogen Activation in Electron Cyclotron Resonance Discharge Sustained by 24 GHz Gyrotron Radiation

We report the results of the first experiments on the growth of indium nitride films by electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition. Discharge sustained by the radiation of a technological gyrotron with a frequency of 24 GHz and power up to 5 kW was used to provide active nitrogen flow. The use of higher frequency microwave radiation for plasma heating provides a higher plasma density, and more active nitrogen flow. Mirror-smooth homogeneous hexagonal InN films were grown on ittria-stabilized zirconia and sapphire substrates. It was shown that single-crystal InN films can be grown on Al2O3 (0001) substrates if a double buffer layer of InN/GaN is used. The growth rate of 1 µm/h was demonstrated in this case. Film properties are studied by optical and electron microscopies, secondary ion mass spectroscopy, X-ray diffraction, and photoluminescence.