Vibrio cholerae Hemagglutinin/Protease Inactivates CTXφ

Pathogenic strains of Vibrio cholerae are lysogens of the filamentous phage CTXφ, which carries the genes for cholera toxin (ctxAB). We found that the titers of infective CTXφ in culture supernatants of El Tor CTXφ lysogens increased rapidly during exponential growth but dropped to undetectable levels late in stationary-phase growth. When CTXφ transducing particles were mixed with stationary-phase culture supernatants of El Tor strains, CTXφ infectivity was destroyed. Our data indicate that this growth phase-regulated factor, designated CDF (CTXφ-destroying factor), is the secreted hemagglutinin/protease (HA/P) of V. cholerae. A strain containing a disrupted hap gene, which encodes HA/P of V. cholerae, did not produce CDF activity in culture supernatants. Introduction of the HA/P-expressing plasmid pCH2 restored CDF activity. Also, CDF activity in culture supernatants of a variety of pathogenic V. cholerae isolates varied widely but correlated with the levels of secreted HA/P, as measured by immunoblotting with anti-HA/P antibody. CDF was purified from V. cholerae culture supernatants and shown to contain a 45-kDa polypeptide which bound anti-HA/P antibodies and which comigrated with HA/P in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The production of high levels of secreted HA/P by certain V. cholerae strains may be a factor in preventing CTXφ reinfection in natural environments and in the human host.