Presence of small plasmids in fixed pathogenic L forms of Agrobaderium tumefaciens

Summary We studied the presence of small plasmids in fixed pathogenic L forms of Agrobacterium tumefaciens obtained from the strain ATV of A. tumefaciens isolated from grapes. Electron microscopy revealed a widespread distribution of the contour length of 137 molecules of covalently closed circular-DNA (CCC-DNA). We found, at least, two different molecular size classes. The molecular weight of the plasmids of the fixed L forms of A. tumefaciens were estimated to be 0.51 and 0.91 Md. Possible functions of these plasmids are considered.