Recombinant plasmids capable of replication in B. subtilis and E. coli

Summary

The plasmid pBC16 (4.25 kbases), originally isolated from Bacillus cereus, determines tetracycline resistance and can be transformed into competent cells of B. subtilis. A miniplasmid of pBC16 (pBC16-1), 2,7 kb) which has lost an EcoRI fragment of pBC16 retains the replication functions and the tetracycline resistance. This plasmid which carries only one EcoRI site has been joined in vitro to pBS1, a cryptic plasmid previously isolated from B. subtilis and shown to carry also a single EcoRI site (Bernhard et al., 1978). The recombinant plasmid is unstable and dissociates into the plasmid pBS161 (8.2 kb) and the smaller plasmid pBS162 (2.1 kb). Plasmid pBS161 retains the tetracycline resistance. It possesses a single EcoRI site and 6 HindIII sites. The largest HindIII fragment of pBS161 carries the tetracycline resistance gene and the replication function. After circularization in vitro of this fragment a new plasmid, pBS161-1 is generated, which can be used as a HindIII and EcoRI cloning vector in Bacillus subtilis.

Hybrid plasmids consisting of the E. coli plasmids pBR322, pWL7 or pAC184 and different HindIII fragments of pBS161 were constructed in vitro. Hybrids containing together with the E. coli plasmid the largest HindIII fragment of pBS161 can replicate in E. coli and B. subtilis. In E. coli only the replicon of the E. coli plasmid part is functioning whereas in B. subtilis replication of the hybrid plasmid is under the control of the Bacillus replicon. The tetracycline resistance of the B. subtilis plasmid is expressed in E. coli, but several antibiotic resistances of the E. coli plasmids (ampicillin, kanamycin and chloramphenicol) are not expressed in B. subtilis. The hybrid plasmids seem to be more unstable in B. subtilis than in E. coli.