Changes in properties of phytopathogenic bacteria effected by plasmid pRD1

Transfer of plasmid pRD1 from Escherichia coli K 12J62 -1 to phytopathogenic bacteria, Agrobacterium tumefaciens, Xanthomonas beticola and Erwinia carotovora subsp. carotovora caused changes in conjugant properties not determined by the plasmid and the emergence of the properties not present in the parent strains. Clones have been obtained with intermediate properties between donor and recipient, including those with altered or lost virulence. In transconjugants of A. tumefaciens virulence increased. In transconjugants of X. beticola and E. carotovora subsp. carotovora highly virulent as well as avirulent forms have been observed. The loss of virulence in X. beticola correlated with the Nif+ phenotype. Plasmid pRD1 also affected the biochemical properties of the new hosts.