Megaplasmids in the plant-associated bacteria Rhizobium meliloti and Pseudomonas solanacearum

Using analytical and preparative methods, we demonstrated the presence of megaplasmids with molecular weight larger than 450 x 10(6) in the two plant-associated bacteria Rhizobium meliloti and Pseudomonas solanacearum. Such giant plasmids were found in 8 of 9 P. solanacearum strains tested and in all of the 18 R. meliloti strains tested.