CTX phi, infection of Vibrio cholerae requires the tolQRA gene products

CTX phi is a lysogenic filamentous bacteriophage that encodes cholera toxin. Filamentous phages that infect Escherichia coli require both a pilus and the products of tolQRA in order to enter host cells. We have previously shown that toxin-coregulated pilus (TGP), a type IV pilus that is an essential Vibrio cholerae intestinal colonization factor, serves as a receptor for CTX phi. To test whether CTX phi also depends upon tol gene products to infect V. cholerae, we identified and inactivated the V. cholerae tolQRAB orthologues. The predicted amino acid sequences of V. cholerae TolQ, TolR, TolA, and TolB showed significant similarity to the corresponding E. coli sequences. V. cholerae strains with insertion mutations in tolQ, tolR, or tolA were reduced in their efficiency of CTX phi uptake by 4 orders of magnitude, whereas a strain with an insertion mutation in tolB showed no reduction in CTX phi entry. We could detect CTX phi infection of TCP- V. cholerae, albeit at very low frequencies. However, strains with mutations in both tcpA and either tolQ, tolR, or tolA were completely resistant to CTX phi infection. Thus, CTX phi, like the E. coli filamentous phages, uses both a pilus and TolQRA to enter its host. This suggests that the pathway for filamentous phage entry into cells is conserved between host bacterial species.