Isolation and Partial Characterization of Three Cryptic Plasmids from Strains of Clostridium butyricum

Of seven strains of Clostridium butyricum examined, four contained covalently closed circular DNA molecules. The bacteriocinogenic strain C. butyricum NCIB 7423 carried two plasmids: pCB101 of molecular mass 3·9 megadaltons (5·6 × 103 bases) and pCB102 of molecular mass 5·2 megadaltons (7·4 × 103 bases). Plasmid pCB101 was not restricted by EcoRI which cleaved pCB102 at two sites; both plasmids were restricted by HindIII. The three other plasmid-bearing strains of C. butyricum (SA1, SA11 and NCTC 6084) each carried a single plasmid of molecular mass 4·3 megadaltons (6·2 × 103 bases) with a single cleavage site for EcoRI and four sites for HindIII, the fragments so produced from the three plasmids being indistinguishable on agarose gel electrophoretograms. It was concluded that the three strains harboured a common plasmid - pCB103.