[ Objective] This study aimed to select E. coli strains with phage-resistance. [ Method] Phage-resistant strains of E. coli glyA genetic engineering bacteria were selected by phage induction and UV-coupling phage indu...[ Objective] This study aimed to select E. coli strains with phage-resistance. [ Method] Phage-resistant strains of E. coli glyA genetic engineering bacteria were selected by phage induction and UV-coupling phage induction. [ Result] By phage induction, 20 strains with stable resistance were selected from the 24 phage-resistant strains, only one strain showed better growth condition than the original strains, but the enzymatic activities of the 20 strains were all lower than the original strains; 41 phage-resistant strains were selected by UV-coupling phage induction, 39 strains of which had better stability, including 7 strains that showed better growth conditions than the original strains and two strains had higher enzymatic activities than the original strains. [ Conclusion] UV-coupling phage induction is a suitable method to select phage-resistant strains from Ecoli genetic engineering bacteria.展开更多
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
文摘[ Objective] This study aimed to select E. coli strains with phage-resistance. [ Method] Phage-resistant strains of E. coli glyA genetic engineering bacteria were selected by phage induction and UV-coupling phage induction. [ Result] By phage induction, 20 strains with stable resistance were selected from the 24 phage-resistant strains, only one strain showed better growth condition than the original strains, but the enzymatic activities of the 20 strains were all lower than the original strains; 41 phage-resistant strains were selected by UV-coupling phage induction, 39 strains of which had better stability, including 7 strains that showed better growth conditions than the original strains and two strains had higher enzymatic activities than the original strains. [ Conclusion] UV-coupling phage induction is a suitable method to select phage-resistant strains from Ecoli genetic engineering bacteria.
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.
