Cloning and characterization of a novel haemolysin in Vibrio cholerae O1 that does not directly contribute to the virulence of the organism.

A previously undescribed haemolysin, distinct from the major Vibrio cholerae O1 El Tor haemolysin, HlyA, was cloned from the O1 classical biotype strain Z17561. This novel haemolysin showed 71.5% overall similarity to the delta-thermostable direct haemolysin of Vibrio parahaemolyticus, and so it has been termed V. cholerae delta-thermostable haemolysin (Vc-deltaTH, encoded by the dth gene). An ORF found immediately downstream, which appears to be transcriptionally and translationally linked to dth, displayed strong homology to the family of acyl-CoA synthetases. When expressed from an inducible promoter in Escherichia coli, Vc-deltaTH was shown to be a 22.8 kDa protein active on sheep red blood cells. Co-expression of acs with dth had no effect on the haemolytic activity or cytoplasmic localization of Vc-deltaTH. A V. cholerae Z17561 dth::Km(R) mutant showed unaltered behaviour in the infant mouse cholera model.