In El Tor biotype strains of toxigenic Vibrio cholerae, the CTX? prophage often resides adjacent to a chromosomally integrated satellite phage genome, RS1, which produces RS1? particles by using CTX prophage-encoded morphogenesis proteins. RS1 encodes RstC, an antirepressor against the CTX? repressor RstR, which cooperates with the host-encoded LexA protein to maintain CTX? lysogeny. We found that superinfection of toxigenic El Tor strains with RS1?, followed by inoculation of the transductants into the adult rabbit intestine, caused elimination of the resident CTX prophage-producing nontoxigenic derivatives at a high frequency. Further studies using recA deletion mutants and a cloned rstC gene showed that the excision event was recA dependent and that introduction of additional copies of the cloned rstC gene instead of infection with RS1? was sufficient to enhance CTX? elimination. Our data suggest that once it is excised from the chromosome, the elimination of CTX prophage from host cells is driven by the inability to reestablish CTX? lysogeny while RstC is overexpressed. However, with eventual loss of the additional copies of rstC, the nontoxigenic derivatives can act as precursors of new toxigenic strains by acquiring the CTX prophage either through reinfection with CTX? or by chitin-induced transformation. These results provide new insights into the role of RS1? in V. cholerae evolution and the emergence of highly pathogenic clones, such as the variant strains associated with recent devastating epidemics of cholera in Asia, sub-Saharan Africa, and Haiti.
Animals Bacterial Proteins