Physical characterisation of plasmids in a morpholine-degrading mycobacterium

The plasmid content of an environmental mycobacterium (MorG) which degrades morpholine (Mor+ phenotype) was investigated. The combination, in what appears to be a novel way, of restriction endonuclease digestion, gel electrophoresis and scanning densitometry permitted the resolution of mixed plasmid preparations into four distinct plasmids with sizes of 54 (approximately), 27.7, 22.8 and 22.6 kb. These plasmids were named pMOR1, 2, 3 and 4, respectively. The Mor+ phenotype was found to be unstable during acriflavin treatment. In four independently isolated Mor- mutants, plasmid pMOR2 was found to have acquired an insert of approximately 1.8 kb within a specific 5.9 kb BamHI fragment. It is concluded that pMOR2 is involved in the coding of the Mor+ phenotype.