Some factors affecting the copy number of specific plasmids in Bacillus species

Some factors affecting the copy number of specific plasmids in different hosts were presented. A low copy number (one copy per chromosome) Kmr Tcr plasmid pTB19 was isolated from thermophilic bacillus. We have constructed 22 derivatives from pTB19 and their copy numbers range from 1 to 214 per chromosome in B. subtilis and B. stearothermophilus. Some recombinant plasmids containing the specific 1.0-MDa EcoRI fragment exhibited high transformation frequency and low copy number in B. stearothermophilus and were stable in the thermophile; on the other hand, those plasmids were unstable in different host B. subtilis, as mentioned earlier. By selecting the best combination of vector plasmid and host strain, both molecular cloning of various enzyme genes (i.e., penicillinase, thermostable alpha-amylase, and thermostable neutral protease) and enhancement of the enzyme production could be easily achieved.