Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of...Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of a mutation spectrum appears to be consistent, but direct proof of such results in vivo are limited. Using mutS, dam and/or dcm defective Eschericha coli imitator strains, an preliminary experimental system on induction of in vivo mutation spectra of low energy N+ ion beam has been established in this study. It was observed that the mutation rates of rifampicin resistance induced by N+ implantation were quite high, ranging from 9.2 x 10~8 to 4.9× 10~5 at the dosage of 5.2×1014 ions/cm2. Strains all had more than 90-fold higher mutation rate than its spontaneous mutation rate determined by this method. It reveals that base substitutions involve in induction of mutation of low energy nitrogen ion beam implantation. The mutation rates of mutator strains were nearly 500-fold (GM2929), 400-fold (GM5864) and 6-fold larger than that of AB1157. The GM2929 and GM5864 both lose the ability of repair DNA mismatch damage by virtue of both dam and dcm pathways defective (GM2929) or failing to assemble the repair complex (GM5864) respectively. It may explain the both strains had a similar higher mutation rate than GM124 did. It indicated that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N+ implantation. The further related research were also discussed.展开更多
Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the...Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the E.coli wild type and mutator strains, the mutant frequencies suggest that base substitutions in rpoB gene are induced by the N + implantation. A highly conserved region is selected to get the direct evidence for base substitutions by sequence of the high fidelity PCR amplification products in mutants. Most of the mutants (90.9%, 40/44) have at least one base substitution in the amplification region. The evidences for CG to TA (55%, 22/40), AT to GC (20%, 8/40) and TA to CG (5%, 2/40) transitions are identified. The transversions are AT to TA (15%, 6/40) and GC to CG (5%, 2/40). It is suggested that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N + implantation by analysis of the mutant frequencies of mutator strains.展开更多
[Objective] This study aimed to explore the mutagenesis effects of N＋ ion beam implantation on Streptomyces a/bus and obtain high-yield salinomycin- producing mutant strain. [ Method ] Streptomyces a/bus strain S-11-...[Objective] This study aimed to explore the mutagenesis effects of N＋ ion beam implantation on Streptomyces a/bus and obtain high-yield salinomycin- producing mutant strain. [ Method ] Streptomyces a/bus strain S-11-04 was mutated with different doses of N ＋ implantation. The effects of low energy N ＊ implantation on the survival rate, colony morphology and salinomycin-producing ability were investigated. [ Result] The results showed that low energy N ＋ implantation can efficiently improve the positive mutation rate of Streptomyces albus; 13 mutant strains with high yield of salinomycin were isolated; to be specific, mutant strain N3- 6 has relatively good genetic stability with four continuous generations, and the titres of salinomycin were increased by 41% in the shake-flask culture and 20.5% in mass production compared with the control. [ Conclusion ] N ＋ ion beam irradiation is an effective method to obtain high-yield salinomycin-producing Streptomy- ces albus strain.展开更多
Though the radiation-resistant bacteria Deinococcus radiodurans (D. radiodurans) have a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these...Though the radiation-resistant bacteria Deinococcus radiodurans (D. radiodurans) have a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. In this report, the superoxide dismutase (SOD) and catalase (CAT) activities produced in bacteria (D.radiodurans AS1.633) and their change caused by 20 keV N+ beam exposure were examined. Results showed that the activities of the enzymes were increased in the case of N+ beam exposure from 8×1014 ions/cm2 to 6×1015 ions/cm2. In addition, the treatment of H2O2 and [CHCl3+CH3CH2OH] and the measurement of absorption spectrum showed that the increase of whole SOD activity resulted from inducible activities of Mn-SOD in (a sub^type) D.radiodurans AS1.633. These results suggested that these bacteria possess inducible defense mechanisms against the deleterious effects of oxidization.展开更多
The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability ...The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability s<sub>o</sub> increases linearly from 0 to 0.03 as normal component of translational energy of the molecuar beam E<sub>n</sub> increases from 11.00 to 19.91 kcal/mol for N<sub>2</sub>/Ni system and S<sub>0</sub> from 0 to 0. 10 as E<sub>n</sub> from 10. 40 to 19.91 kcal/mol for N<sub>2</sub>/La system. The apparent activation energy △E are 6.16 kcal/mol and 5.30 kcal/mol for N<sub>2</sub>/Ni and N<sub>2</sub>/La systems respectively.展开更多
We demonstrate nearly i e V GaN0.03As0.97 /In0.09 Ga0.91As strain-compensated short-period superlattice solar cells by all solid-state molecular beam epitaxy. The optimal period thickness for the superlattice growth i...We demonstrate nearly i e V GaN0.03As0.97 /In0.09 Ga0.91As strain-compensated short-period superlattice solar cells by all solid-state molecular beam epitaxy. The optimal period thickness for the superlattice growth is achieved to realize high structural quality. Meanwhile, the annealing conditions are optimized to realize a pho- toluminescence （PL） at a low temperature. However, no PL signal is detected at room temperature, which could be reflected by a lower open-circuit voltage of the fabricated devices. The GaN0.03As0.97/In0.09Ga0.91As super- lattice solar cells show a reasonably-high short-circuit current density （Jsc） of over lOmA/cm2. Eurthermore, a concentration behavior is measured, which shows a linear relationship between Jsc and concentration ratios. The extrapolated ideality factor and saturated current density by the concentration action are in good agreement with that extracted by the dark case of the p-i-n diodes.展开更多
基金The project supported by the National Nature Science Foundation of China (No. 19890300)
文摘Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of a mutation spectrum appears to be consistent, but direct proof of such results in vivo are limited. Using mutS, dam and/or dcm defective Eschericha coli imitator strains, an preliminary experimental system on induction of in vivo mutation spectra of low energy N+ ion beam has been established in this study. It was observed that the mutation rates of rifampicin resistance induced by N+ implantation were quite high, ranging from 9.2 x 10~8 to 4.9× 10~5 at the dosage of 5.2×1014 ions/cm2. Strains all had more than 90-fold higher mutation rate than its spontaneous mutation rate determined by this method. It reveals that base substitutions involve in induction of mutation of low energy nitrogen ion beam implantation. The mutation rates of mutator strains were nearly 500-fold (GM2929), 400-fold (GM5864) and 6-fold larger than that of AB1157. The GM2929 and GM5864 both lose the ability of repair DNA mismatch damage by virtue of both dam and dcm pathways defective (GM2929) or failing to assemble the repair complex (GM5864) respectively. It may explain the both strains had a similar higher mutation rate than GM124 did. It indicated that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N+ implantation. The further related research were also discussed.
文摘Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the E.coli wild type and mutator strains, the mutant frequencies suggest that base substitutions in rpoB gene are induced by the N + implantation. A highly conserved region is selected to get the direct evidence for base substitutions by sequence of the high fidelity PCR amplification products in mutants. Most of the mutants (90.9%, 40/44) have at least one base substitution in the amplification region. The evidences for CG to TA (55%, 22/40), AT to GC (20%, 8/40) and TA to CG (5%, 2/40) transitions are identified. The transversions are AT to TA (15%, 6/40) and GC to CG (5%, 2/40). It is suggested that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N + implantation by analysis of the mutant frequencies of mutator strains.
文摘[Objective] This study aimed to explore the mutagenesis effects of N＋ ion beam implantation on Streptomyces a/bus and obtain high-yield salinomycin- producing mutant strain. [ Method ] Streptomyces a/bus strain S-11-04 was mutated with different doses of N ＋ implantation. The effects of low energy N ＊ implantation on the survival rate, colony morphology and salinomycin-producing ability were investigated. [ Result] The results showed that low energy N ＋ implantation can efficiently improve the positive mutation rate of Streptomyces albus; 13 mutant strains with high yield of salinomycin were isolated; to be specific, mutant strain N3- 6 has relatively good genetic stability with four continuous generations, and the titres of salinomycin were increased by 41% in the shake-flask culture and 20.5% in mass production compared with the control. [ Conclusion ] N ＋ ion beam irradiation is an effective method to obtain high-yield salinomycin-producing Streptomy- ces albus strain.
基金Supported by the National Natural Science Foundation of China (No. 19605005)
文摘Though the radiation-resistant bacteria Deinococcus radiodurans (D. radiodurans) have a high resistance to the lethal and mutagenic effects of many DNA-damaging agents, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. In this report, the superoxide dismutase (SOD) and catalase (CAT) activities produced in bacteria (D.radiodurans AS1.633) and their change caused by 20 keV N+ beam exposure were examined. Results showed that the activities of the enzymes were increased in the case of N+ beam exposure from 8×1014 ions/cm2 to 6×1015 ions/cm2. In addition, the treatment of H2O2 and [CHCl3+CH3CH2OH] and the measurement of absorption spectrum showed that the increase of whole SOD activity resulted from inducible activities of Mn-SOD in (a sub^type) D.radiodurans AS1.633. These results suggested that these bacteria possess inducible defense mechanisms against the deleterious effects of oxidization.
基金Project supportec by the National Natural Science Foundation of China
文摘The activated chemisorption of N<sub>2</sub> on Ni （poly） and La film was performed on a molecular beam—surface scattering apparatus. Experimental results indicate that the initial sticking probability s<sub>o</sub> increases linearly from 0 to 0.03 as normal component of translational energy of the molecuar beam E<sub>n</sub> increases from 11.00 to 19.91 kcal/mol for N<sub>2</sub>/Ni system and S<sub>0</sub> from 0 to 0. 10 as E<sub>n</sub> from 10. 40 to 19.91 kcal/mol for N<sub>2</sub>/La system. The apparent activation energy △E are 6.16 kcal/mol and 5.30 kcal/mol for N<sub>2</sub>/Ni and N<sub>2</sub>/La systems respectively.
基金Supported by the National Natural Science Foundation of China under Grant No 61274134the University of Science and Technology Beijing Talents Start-up Program under Grant No 06105033the International Cooperation Projects of Suzhou City under Grant No SH201215
文摘We demonstrate nearly i e V GaN0.03As0.97 /In0.09 Ga0.91As strain-compensated short-period superlattice solar cells by all solid-state molecular beam epitaxy. The optimal period thickness for the superlattice growth is achieved to realize high structural quality. Meanwhile, the annealing conditions are optimized to realize a pho- toluminescence （PL） at a low temperature. However, no PL signal is detected at room temperature, which could be reflected by a lower open-circuit voltage of the fabricated devices. The GaN0.03As0.97/In0.09Ga0.91As super- lattice solar cells show a reasonably-high short-circuit current density （Jsc） of over lOmA/cm2. Eurthermore, a concentration behavior is measured, which shows a linear relationship between Jsc and concentration ratios. The extrapolated ideality factor and saturated current density by the concentration action are in good agreement with that extracted by the dark case of the p-i-n diodes.
