Studies on Mutation Breeding of High-Yielding Xylanase Strains by Low-Energy Ion Beam Implantation

As a new mutagenetic method, low-energy ion implantation has been used widely in many research areas in recent years. In order to obtain some industrial strains with high xylanase yield, the wild type strain Aspergillus niger A3 was mutated by means of nitrogen ions implantation （10 keV, 2.6× 10^14 ～ 1.56 × 10^15 ions/cm^2） and a mutant N212 was isolated subsequently. However, it was found that the initial screening means of the high-yielding xylanase strains such as transparent halos was unfit for first screening. Compared with that of the wild type strain, xylanase production of the mutant N212 was increased from 320 IU/ml to 610 IU/ml, and the optimum fermentation temperature was increased from 28 ℃ to 30 ℃.

Impact of Low-Energy Ion Beam Implantation on the Expression of Ty1-copia-like Retrotransposons in Wheat(Triticum aestivum)

Retrotransposon-like elements are major constituents of most eukaryotic genomes. For example, they account for roughly 90% of the wheat （Triticum aestivum） genome, Previous study on a wheat strain treated by low-energy N^＋ ions indicated the variations in AFLP （Amplified Fragment Length Polymorphism ） markers, One such variation was caused by the re-activation of Tyl-copia-like retrotransposons, implying that the mutagenic effects of lowenergy ions might work through elevated activation of retrotransposons, In this paper an expression profile of Tyl-copia-like retrotransposons in wheat treated by low-energy N^＋ ions is reported, The reverse transcriptase （RT） domains of these retrotransposons were amplified by reverse-transcriptional polymerase chain reaction （RT-PCR） and sequentially cloned, 42 and 65 clones were obtained from the treated （CL） and control materials （CK）, respectively, Sequence analysis of each clone was performed by software. Phylogeny and classification were calculated responding to the sequences of the RT domains. All the results show that there is much difference in the RT domain between the control sample and the treated sample, Especially, the RT domains from the treated group encode significantly more functional ORF （open reading frames） than those from the control sample, This observation suggests that the treated sample has higher activation of retrotransposons, possibly as a consequence of low-energy ion beam irradiation, It also suggests that retrotransposons in the two groups impact the host gene expression in two different ways and carry out different functions in wheat cells.

Optimization of L-lactic Acid Production of Rhizopus Oryzae Mutant RLC41-6 by Ion Beam Implantation at Low-Energy

In order to obtain an industrial strain with a higher L（＋）-lactic acid yield, the strain Rhizopus oryzae RF3608 was mutated by means of nitrogen ion beam implantation and the mutant strain RLC41-6 was isolated. Under optimal conditions the yield of L（＋）-lactic acid produced in a shake-flask reached 133 g/L - 137 g/L after 36 h cultivation, indicating that the conversion rate based on glucose was as high as 88% - 91% and the productivity was 3.75 g/L.h. It was almost a 115% increase in lactic acid production compared with the original strain RF3608.

Optimization of L(+)-Lactic Acid Production from Xylose with Rhizopus Oryzae Mutant RLC41-6 Breeding by Low-Energy Ion Implantation

In order to obtain an industrial strain with a higher L（＋）-lactic acid yield, the strain Rhizopus oryzae PW352 was mutated by means of nitrogen ion beam implantation and the mutant strain Rhizopus oryzae RLC41-6 was obtained. An experimental finding was made in surprise that Rhizopus oryzae mutant RLC41-6 is not only an L（＋）-lactic acid producer from corn starch but also an efficient producer of L（＋）-lactic acid from xylose. Under optimal conditions, the production of L（＋）-lactic acid from 100 g/L xylose reached 77.39 g/L after 144 h fed-batch fermentation, A high mutation rate and a wide mutation spectrum of low-energy ion implantation were observed in the experiment.

The Effects of Low-Energy Nitrogen Ion Implantation on Pollen Exine Substructure and Pollen Germination of Cedrus deodara

The aim of this study is to investigate the biological effects of ion beams on pollen. Pollen grains of Cedrus deodara were implanted with 30 keV nitrogen ion beams at doses ranging from 1 × 10^15 ions/cm^2 to 15 × 10^15 ions/cm^2. The effects of N^＋ implantation on the pollen exine substructure were examined using an atomic force microscope （AFM）, and the structure and morphology of pollen and pollen tubes were observed using a laser scanning confocal microscope （LSCM）. AFM observations distinctly revealed the erosion of the pollen exine caused by N^＋ implantation in the micrometer to nanometer range. Typical results showed that the erosion degree was linearly proportional to the ion dose. Pollen germination experiments in vitro indicated that N^＋ implantation within a certain dose range increased the rate of pollen germination. The main abnormal phenomena in pollen tubes were also analyzed. Our results suggest that low energy ion implantation with suitable energy and dosage can be used to break the pollen wall to induce a transfer of exogenous DNA into the pollen without any damage to the cytoplasm and nuclei of the pollen. The present study suggests that a combination of the method of ion-beam-induced gene transfer and the pollen-tube pathway method （PTPW） would be a new plant transformation method.

Breeding of Coenzyme Q_(10) Produced Strain by Low-Energy Ion Implantation and Optimization of Coenzyme Q_(10) Fermentation

In order to increase the production efficiency of coenzyme Q10, the original strain Agrobacterium tumefaciens ATCC 4452 was mutated by means of Nitrogen ions implantation. A mutant strain, ATX 12, with high contents of coenzyme Q10 was selected. Subsequently, the conditions such as carbohydrate concentration, nitrogen source concentration, inoculum＇s size, seed age, aeration and temperature which might affect the production of CoQ10 were investigated in detail. Under optimal conditions, the maximum concentration of the intracellular CoQ10 reached 200.3 mg/L after 80 h fed-batch fermentation, about 245% increasing in CoQ10 production after ion implantation, compared to the original strain.

Formation of Nanoscale Intermetallic Phases in Ni Surface Layer at High Intensity Implantation of Al Ions

The results of experimental study of nanoscale intermetallic formation in surface layer of a metal target at ion implantation are presented. To increase the thickness of the ion implanted surface layer the high intensive ion implantation is used. Compared with the ordinary ion implantation, the high intensive ion implantation allows a much thicker modified surface layer. Pure polycrystalline nickel was chosen as a target. Nickel samples were irradiated with Al ions on the vacuum-arc ion beam and plasma flow source 'Raduga-5'. It was shown that at the high intensity ion implantation the fine dispersed particles of Ni3AI, NiAl intermetallic compounds and solid solution Al in Ni are formed in the nickel surface layer of 200 nm and thicker. The formation of phases takes place in complete correspondence with the Ni-AI phase diagram.

Hydrogenation of zirconium film by implantation of hydrogen ions

In order to understand the dnve-in target in a D-D type neutron generator,it is essential to study the mechanism of the interaction between hydrogen ion beams and the hydrogenabsorbing metal film.The present research concerns the nucleation of hydride within zirconium film implanted with hydrogen ions.Doses of 30 keV hydrogen ions ranging from 4.30×10^（17） to1.43×10^（18） ions cm^（-2） were loaded into the zirconium film through the ion beam implantation technique.Features of the surface morphology and transformation of phase structures were investigated with scanning electron microscopy,atomic force microscopy and x-ray diffraction.Confirmation of the formation of 5 phase zirconium hydride in the implanted samples was first made by x-ray diffraction,and the different stages in the gradual nucleation and growth of zirconium hydride were then observed by atomic force microscope and scanning electron microscopy.

XPS INVESTIGATION OF NITROGEN IONS IMPLANTED INTO ALUMINUM ALLOY BY PLASMA BASED ION IMPLANTATION

Aluminum alloy 2024 has been implanted with nitrogen ions at various doses by plasma based ion implantation. The introduction of energetic ions causes structural change within the near surface region of the solid. The samples have been characterized by X-ray Photoelectron Spectroscopy at various depths. The chemical states of Al and N were identified by deconvolution of the recorded XPS spectra. After plasma based ion implanted nitrogen into aluminum, not only the AlN precipitates but also super saturated solution of nitrogen forms. The presence of aluminum in different chemical states is corresponding to Al, AlN and Al2O3. The majority of nitrogen is in the form of the supersaturated solution. With the increase of nitrogen dose, the amount of AlN precipitates increases.

A Study of Mutation Breeding of High-Yielding Tryptophanase Escherichia coli by Low-Energy N^+ Ion Beam Implantation

Low energy ion beam has been widely applied in microbe breeding, plant breeding, gene transfer and cell modification. In this study, the Escherichia coli （E.coli） strain producing tryptophanase was irradiated by a low energy nitrogen ion beam with an energy of 10 keV at a fluence of 13 × 10^14 N^＋/cm^2 when glycerin at a 15% concentration was used as a protector. The effect on the biomass of E. coli after N^＋ implantation was analyzed in detail by statistic methods. The screening methods used in this study were proven to be effective. After continuous mutagenicity, a high-yield tryptophanase strain was selected and both its biomass and enzymatic activity were higher than those of the parent strain. The results of scale-up production showed that the biomass could reach wet weight 8.2 g/L and 110 g L-tryptophan could be formed in the volume of the 1 l enzymatic reaction system.

MODIFICATION OF SURFACE MECHANICAL PROPERTIES OF POLYCARBONATE BY B^+ AND O^+ IONS IMPLANTATION

By implanting B+ and O+ ions respectively into polycarbonate (PC) plates, the surface mechanical properties of PC have been improved. Measurement by Nano Indenter II showed that the hardness of samples increased 7-25 times than that before implantation; and the modulus of elasticity raised 2-5 times. The wear-resistance was tested by ball crusher; the width and depth of the wear-streak decreased by 1/3-1/2 or even more. The structure, deformation and appearance were analyzed by using Micro-FTIR Spectra, ESCA method and the steps instrument. These analyses showed that the structure of PC had been modified: a series of new cross-linking yielded, it depends on the Linear Energy Transition (LET) of implanted ions in the high polymer compounds.

Nitrogen Deposition Via N^+ Implantation:Implications for Primordial Amino Acids Synthesis Revisited

In this paper amino acids synthesis in aqueous solution induced by ion implantation, which was possibly ubiquitous on primitive Earth, is investigated. As a discharge using a graphite rod as the anode under a nitrogen atmosphere was performed against ammonia water, it was found that three kinds of amino acids were produced. They were glycine, serine and alanine. By introducing ion implantation into the carboxylate solution, ammonia and amino acids were also formed via nitrogen deposition/fixation. Another isotopic experiment showed that both OH and H radicals played a crucial role in the arc-discharge-promoted reactions in aqueous solution Therefore, we believe that the impact of ions in the original atmospheric conditions might have functioned as a promoter in the chemical origin and evolution of life.

Effect of Ar Ion Beam Implantation on Morphological and Physiological Characteristics of Liquorice(Glycyrrhiza uralensis Fisch)Under Short-Term Artificial Drought Conditions

Ar^＋ ion beam with low energy of 30 keV was implanted into liquorice （Glycyrrhiza uralensis Fisch） seeds at the doses of 0, 600, 900 and 1200 × （2.6 × 10^13） ions/cm^2, respectively. The seeds were sowed in pots and after one month the plants were subjected to different drought conditions for two months. Then the plants＇ morphological and physiological characteristics, antioxidation enzymes and levels of endogenous hormones were investigated. The results showed that ion implantation at a proper dose can greatly enhance the liquorice seedlings＇ resistance against drought stress.

Modeling of Inner Surface Modification of a Cylindrical Tube by Plasma-Based Low-Energy Ion Implantation

The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications.In this paper,a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias.Using this plasma density distribution as the initial condition,a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time.The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field.The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24,respectively,of which the value is 1 at the central plasma source.After a 5μs pulse-on time,in the area less than 2 cm from the end of the tube,the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°;both variations reduce the nitrogen ion implantation depth.However,the nitrogen ion implantation dose peaks of about 2×10^（10）-7×10^（10）ions/cm^2 in this area are 2-4 times higher than that of 1.18×10^（10）ions/cm^2 and 1.63×10^（10）ions/cm^2 on the inner and outer surfaces of the tube.The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation,because the modification effect is mainly determined by the ion implantation dose,just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion.Therefore,a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.

Mutagenic Effects of BM302:GO112 Induced by Low-Energy Ion Beam Implantation

Mutant strains of GO112 and BM302 with a high 2-keto-L-gulonic acid （2KLG） transformation rate induced by ion beam implantation were separately and combinatorially compared with the original strains GO29 and BM80 to study the mutagenic effects of ion beam implantation. Both the sole GOl12 and mixed BM302：GOl12 demonstrated improved SNDH activity and 2KLG yield compared to the original strains. The mutant combinations of BM302：GOl12 showed a longer stationary phase and higher biomass than BM80：GO29. The mutant BM302 exhibited a stronger capacity to maintain a stable pH environment at mixed fermentation with Gluconobacter oxydans （G. oxydans） for 2KLG transformation and facilitated the growth of G. oxydans compared with the original strain BM80. The promotive capacity to L-sorbosone dehydrogenase （L-SNDH） from the supernate of BM302 was 1.6-fold higher than that of BM80. Genes encoded SNDH in GO29 and GOl12 were amplified and sequenced, and mutations including three transitions （CG →TA, CG →TA, GC → AT） and one transversion （AT→ TA） were confirmed from GO29 to GOl12. The corresponding amino acid was changed as Leu →Phe, Arg → Gln and Asn → Lys.

Optimization of L(+)-Lactic Acid Fermentation Without Neutralisation of Rhizopus Oryzae Mutant RK02 by Low-Energy Ion Implantation

In order to get an industrial strain which can yield a high concentration of lactic acid for ISPR （in situ product removal）, the original strain Rhizopus oryzae RE3303 was mutated by low-energy ion beam implantation. A mutant RK02 was screened, and the factors such as the substrate concentration, nitrogen source concentration, inoculum size, seed age, aeration and temperature that affect the production of lactic acid were studied in detail. Under optimal con- ditions, the maximum concentration of L（＋）-lactic acid reached 34.85 g/L after 30 h shake-flask cultivation without adding any neutralisation （5% Glucose added）, which was a 146% increase in lactic acid production after ion implantation compared with the original strain. It was also shown that RK02 can be used in ISPR to reduce the number of times of separation.

Influence of Aluminum Ions Implantation on Corrosion Behavior of Zircaloy-2 Alloy in 1 M H_2SO_4

The specimens were implanted with aluminum ions with fluence ranging from 1× 10^16 to 1× 10^17 ions/cm^2 to study the effect of aluminum ion implantation on the aqueous corrosion behavior of zircaloy-2 by metal vapor vacuum arc source （MEVVA） at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy （XPS） and Auger electron spectroscopy （AES）, respectively. Transmission electron microscopy （TEM） was used to examine the microstructure of the aluminum-implanted samples. Glancing angle X-ray diffraction （GAXRD） was employed to examine the phase transformation due to the aluminum ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zircaloy-2 in a 1 M H2SO4 solution. It is found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-2 implanted with aluminum ions. Finally, the mechanism of the corrosion behavior of aluminum- implanted zircaloy-2 was discussed.

Effect of copper ions implantation on the corrosion behavior of ZIRLO alloy in 1 mol/L H_2SO_4

In order to study the effect of copper ion implantation on the aqueous corrosion behavior of ZIRLO alloy, specimens were implanted with copper ions with fluences ranging from 1×10^16 to 1×10^ ions/cm^2, using a metal vapor vacuum arc source （MEVVA） at an extraction voltage of 40 kV, The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy （XPS） and Auger electron spectroscopy （AES）, respectively. Glancing angle X-ray diffraction （GAXRD） was employed to examine the phase transformation due to the copper ion implantation. The potcntiodynamic polarization technique was used to evaluate the aqueous corrosion resistance of implanted ZIRLO alloy in a 1 mol/L H2SO4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of ZIRLO alloy implanted with copper ions when the fluence is 5×10^16 ions/cm^2. When the fluence is 1×10^16 or 1×10^17 ions/cm^2, the corrosion resistance of implanted sanaples was bad. Finally, the mechanism of the corrosion behavior of copper-implanted ZIRLO alloy was discussed.

Characteristics of La_0.7Sr_0.3MnO₃Films Modified by Aluminum Ions Implantation and Post-Implantation Annealing

The magnetron sputtered La0.7Sr0.3MnO3 films were implanted with different doses (5 ′ 1015 ions×cm?2 and 5 ′ 1016 ions×cm-2) of Al ions at different negative pulsed voltages (30 kV and 50 kV) by plasma based ion implantation and then annealed at 973 K for 1 h in air. The microstructure, surface morphologies, surface roughness, metal-insulator transition and room temperature emittance properties of the post-implantation annealed films were investigated and compared with those of the La0.7Sr0.3MnO3 film annealed at 973 K for 1 h in air. The results indicate that the post- implantation annealed films show single perovskite phase and obvious (100) preferred orientation growth. The Mn-O bond length, surface roughness and metal-insulator transition temperature (TMI) of the films can be effectively adjusted by changing implantation voltage or implantation dose of Al ions. However, the change of implantation parameters just has a small effect on room temperature emittance of the films. Compared with the annealed film, the post-implantation annealed films have shorter Mn-O bond length and lower room temperature emittance. The TMI of the films implanted at low voltage is lower than that of the annealed film, which mainly results from the degradation of oxidization during annealing process and the part displacement of Mn3+-O2+- Mn4+ double exchange channels by Al3+-O2?-Mn4+. The post-implanted annealed film implanted at 50 kV/5 ′ 1016 ions×cm-2 has a higher TMI than the annealed film, which is 247 K. The increase of TMI of the film implanted with high dose of Al ions at high voltage can be attributed to the improvement of microstructure.