Characterization of the plasmids of Bacillus megaterium: Restriction endonuclease digestions, Southern blotting analysis, and partial denaturation mapping

Three plasmids of the complex plasmid system of Bacillus megaterium strain 216 have been physically characterized by restriction endonuclease digestions, DNA-DNA hybridizations by the Southern blotting technique, and partial denaturation mapping by electron microscopy. The results show that each plasmid size class produces a unique pattern of restriction endonuclease digestion fragments and anneals only to molecules of the same plasmid size. Partial denaturation reveals unique and consistent differential melting patterns for each plasmid. It is concluded that each of these three plasmid species, and probably the larger ones as well, represents a molecular entity of unique and distinct nucleotide sequence, unrelated to each other or to the chromosome of the bacterium.