The R-type pyocin of Pseudomonas aeruginosa C is a bacteriophage tail-likeparticle that contains single-stranded DNA

Pseudomonas aeruginosa R-type pyocin particles have been described as bacte riocins that resemble bacteriophage tail-like structures. Because of their unusual structure, we reexamined whether they contained nucleic acids. Our data indicated that pyocin particles isolated from P. aeruginosa C (pyocin C) contain DNA. Probes generated from this DNA by the random-primer extensi on method hybridized to distinct bands in restriction endonuclease-digested P. aeruginosa C genomic DNA. These probes also hybridized to genomic DNA f rom 6 of 18 P. aeruginosa strains that produced R-type pyocins. Asymmetric PCR, complementary oligonucleotide hybridization, and electron microscopy i ndicated that pyocin C particles contained closed circular single-stranded DNA, approximately 4.0 kb in length. Examination of total intracellular DNA from mitomycin C-induced cultures revealed the presence of two extrachromo somal DNA molecules, a double-stranded molecule and a single-stranded molec ule, which hybridized to pyocin DNA. Sequence analysis of 7,480 nucleotides of P. aeruginosa C chromosomal DNA containing the pyocin DNA indicated the presence of pyocin open reading frames with similarities to open reading f rames from filamentous phages and cryptic phage elements. We did not observ e any similarities to known phage structural proteins or previously charact erized pseudomonal prt genes expressing R-type pyocin structural proteins. These studies demonstrate that pyocin particles from P. aeruginosa C are de fective phages that contain a novel closed circular single-stranded DNA and that this DNA was derived from the chromosome of P. aeruginosa C.