Study of the Plasmid Instability in Corynebacterium
棒杆菌宿主中质粒不稳定性的研究

Recombinant plasmid pNAR4, which can be used as shuttle vector between E. coli and coryneform bacteria, was constructed by ligation the DNA fragments of pNAT65 and pACYC177. Plasmid instability was found when pNAR4 was transformed into various coryneform bacteria strains, segregational instability in C. crenatum B9 and structural instability in C. glutamicum 10147 and C. crenatum T6-13. When pNAT65 was transformed into C. glutamicum 10147,the plasmid in transformants were found different to pNAT65. The size and main restriction sites in these plasmids were identical with that, of pXZl0145. DNA hybridization experiments indicated that in C. glutamicum 10147, there was a supercoiled DNA content which was highly homologous with pXZ10145, An assumption is given here in which the existence of this supercioled DNA content is related to the phenomena of various plasmid instabilityMand inter-or/and intra-molecular recombination may be the reason to explain the related phenomena found in our work.