Determination and in vivo characterization of the basic replicon of natural plasmids of Methylomonas clara

The basic replicon of the endogenous Methylomonas clara plasmid pBE-2 and its derivatives was defined to a region of 2.7 kb by in vivo deletions and conjugative transfer experiments using Escherichia coli-M. clara hybrid plasmids. Origin activity was found to be confined to a maximal length of 1.3 kb. The origin consists of two fragments which can be separated more than 4 kb by the integration of foreign DNA fragments without loss of function. A fragment having a maximum size of 2.1 kb supports in trans replication initiation at the origin. In addition, two incompatibility determinants were revealed, one localized in the origin fragment and the other outside the origin. Incompatibility between two basic replicons of the natural M. clara plasmids can be overcome by the integration of one of them in the compatible IncP plasmid R68-Km^s. No homology was found between the plasmid basic replicon and the chromosomal DNA of M. clara.