ISOLATION AND CHARACTERIZATION OF PLASMIDS FROM DIFFERENT STRAINS OF METHANOBACTERIUM-THERMOFORMICICUM

Seven strains of the formate-utilizing thermophilic methanogen Methanobacterium thermoformicium were screened for the presence of extrachromosomal DNA. Covalently closed circular plasmid DNA was detected in three strains, Z-245, FTF and THF. No plasmids were found in strains CB12 and SF-4, nor in two new isolates, FF1 and FF3. The plasmid from strain Z-245, designated pFZ1, and that from strain FTF, designated pFZ2, were approximately 10.5 kb in size and contained homologous and similarly sized restriction fragments. A physical map of plasmid pFZ1 was constructed and three KpnI-fragments comprising the entire plasmid were cloned in Escherichia coli using pUC19. Plasmid pFV1 isolated from strain THF was approximately 14 kb in size and contained regions with strong homology to pFZ1 DNA. Using the Methanobacterium formicium fdhA gene as a hybridization probe the strains of the species M. thermoformicicum could be classified into two major groups.