INSTABILITY OF HYBRID PLASMIDS IN BACILLUS-SUBTILIS

We studied the mechanisms responsible for instability of hybrid deriva tives of staphylococcal R plasmids in B. subtilis cells. Four pBCH pla smids were constructed from staphylococcal chloramphenicol-resistance plasmid pC756 ligated with pBR322 or pUC8 vectors, and two pAEC plasmi ds contained pC756 plasmid, erm gene from S. aureus pE3692 and pBR322 plasmid vector. The level of instability of these recombinant plasmids was clearly related to their sizes, the larger derivatives were segre gationally highly unstable.The four hybrid pBE plasmids constructed fr om erythromycin-resistant pE3692 plasmid or its deletion derivative an d pBR322 vector were poorly maintained in B. subtilis rec+ strain in c omparison with the B. subtilis (recE4) strain. Moreover, the absence i n pBE-hybrids of a part of palA sequence led to considerable reduction of plasmid stability in B. subtilis cells. However, the clones of B.s ubtilis harbouring pBE plasmids integrated into the bacterial chromoso me presented much higher stability of the plasmid erm gene than the cl ones maintaining autonomously replicating plasmids.