FIG. 1.

Reporter plasmids and strains used to assay Lp02 competence. (A) Reporter plasmids used for transforming L. pneumophila were constructed by first cloning a 3-kb piece of L. pneumophila DNA into pBluescript II KS⁺ to generate plasmid pJB955. Three pJB955 derivatives (pJB1389, pJB964, and pJB957) were constructed by cloning a gentamicin, chloramphenicol, or kanamycin resistance cassette, respectively, into the unique HindIII site in the 3-kb insert. (B) Two Lp02-derived reporter strains were used to assay natural competence. JV1103, a Cm^r-marked version of Lp02, was constructed by natural transformation using plasmid pJB964. JV1160, a Kan^r-marked version of Lp02, was constructed by natural transformation using plasmid pJB957. With these strains and plasmids, successful recombination can be assessed not only by gain of a drug resistance marker from the transforming reporter plasmid but also by loss of a drug resistance marker from the reporter strain.