Plasmid transfer into members of the family Legionellaceae.

The plasmids RP4 and pPH1JI::Mu::Tn5 were transferred with moderate frequency from Escherichia coli to Legionella pneumophila (strain Bloomington 2) and Fluoribacter (Legionella) bozemanae (strain WIGA). The frequency of transfer to Tatlockia (Legionella) micdadei (strain Tatlock) was much lower. In these transconjugant strains the plasmids were maintained following at least 10 nonselective passages. However, the introduced plasmids could not be transferred from these strains to several other strains of Legionella or Tatlockia with a detectable frequency, yet they could be transferred to a restriction-modification deficient (rm-) E. coli strain with moderate frequency. This suggests not only that the expression of transfer genes may be repressed but that the legionellae are poorer recipients than are the rm- E. coli.