Characterization of a small endogenous plasmid from the CyanobacteriumPlectonema boryanum

The nonheterocystous filamentous CyanobacteriumPlectonema boryanum strain UTEX 594 contains at least two plasmids. A small 145 kb plasmid was cloned in pBR322. It has no homology with the bigger resident plasmid or with chromosomal DNA. A small fraction of the plasmid is present in the form of multimers or concatemers. Copy number and hybridization patterns of the plasmid were similar under dinitrogen-fixing and non-fixing conditions. Restriction site mapping of the plasmid was done to enable its use in the development of cyanobacterial cloning vectors. It is among the smallest natural plasmids reported from bacteria.