Characterization of the dsDNA prophage sequences in the genome of Neisseria gonorrhoeae and visualization of productive bacteriophage.

BACKGROUND: Bioinformatic analysis of the genome sequence of Neisseria gonorrhoeae revealed the presence of nine probable prophage islands. The distribution, conservation and function of many of these sequences, and their ability to produce bacteriophage particles are unknown. RESULTS: Our analysis of the genomic sequence of FA1090 identified five genomic regions (NgoPhi1 - 5) that are related to dsDNA lysogenic phage. The genetic content of the dsDNA prophage sequences were examined in detail and found to contain blocks of genes encoding for proteins homologous to proteins responsible for phage DNA replication, structural proteins and proteins responsible for phage assembly. The DNA sequences from NgoPhi1, NgoPhi2 and NgoPhi3 contain some significant regions of identity. A unique region of NgoPhi2 showed very high similarity with the Pseudomonas aeruginosa generalized transducing phage F116. Comparative analysis at the nucleotide and protein levels suggests that the sequences of NgoPhi1 and NgoPhi2 encode functionally active phages, while NgoPhi3, NgoPhi4 and NgoPhi5 encode incomplete genomes. Expression of the NgoPhi1 and NgoPhi2 repressors in Escherichia coli inhibit the growth of E. coli and the propagation of phage lambda. The NgoPhi2 repressor was able to inhibit transcription of N. gonorrhoeae genes and Haemophilus influenzae HP1 phage promoters. The holin gene of NgoPhi1 (identical to that encoded by NgoPhi2), when expressed in E. coli, could serve as substitute for the phage lambda s gene. We were able to detect the presence of the DNA derived from NgoPhi1 in the cultures of N. gonorrhoeae. Electron microscopy analysis of culture supernatants revealed the presence of multiple forms of bacteriophage particles. CONCLUSION: These data suggest that the genes similar to dsDNA lysogenic phage present in the gonococcus are generally conserved in this pathogen and that they are able to regulate the expression of other neisserial genes. Since phage particles were only present in culture supernatants after induction with mitomycin C, it indicates that the gonococcus also regulates the expression of bacteriophage genes.