A SIMPLIFIED METHOD FOR SCREENING AND CHARACTERIZATION OF PLASMID DNA IN CYANOBACTERIA

Plasmid distribution among 14 different cyanobacteria was studied using a simplified method which involved direct agarose gel electrophoresis of heat-treated, ethanol-precipitated, plasmid preparations from the cleared lysates without requiring ultracentrifugation. The method is sensitive and can be effectively used to determine the number of different plasmid species and their molecular weights from the agarose gel patterns. The results compare well with those obtained by the CsCl-EtBr equilibrium density centrifugation technique. Out of 14 cyanobacteria, eight were found to contain plasmid DNA of size ranging from 0.9 to 35.0 MDa. All the cyanobacteria, viz., Lyngbya, Plectonema and Phormidium, belonging to the LPP group showed different plasmid profiles, supporting the view that these strains are independent isolates of different species. Anabaena azollae did not contain any plasmid DNA.