A plasmid from a virulent strain of Legionella pneumophila is conjugative and confers resistance to ultraviolet light.

The presence of a single apparently cryptic plasmid of approximately 36 MDa was demonstrated in the virulent Dodge strain of Legionella pneumophila. 'Tagging' of the plasmid with Tn5 enabled transfer to be demonstrated to other strains of Legionella (though not to Escherichia coli or Pseudomonas aeruginosa) as well as a definitive assessment to be made of its stability. Plasmid carriage confers resistance to UV light probably by means of an error-prone UV repair system. The plasmid is compatible with plasmids of the IncP and IncW incompatibility groups.