Abstract
Synthesis of alpha-haemolysin by Escherichia coli was proportional to the amount of meat-broth factor present in the medium and not to bacterial growth. The meat-broth component required for the synthesis of haemolysin was found to have several physical and chemical properties in common with alpha-haemolysin itself. Both molecules are trypsin-sensitive, acidic substances with similar elution volumes when subjected to gel-filtration chromatography with Sepharose 6B. Isotopic labelling experiments in which the bacteria were grown on 14C-labelled meat broth showed that partially purified haemolysin preparations contained molecules of mammalian origin. Similar experiments in which 14C-glucose was used to label bacterial molecules showed that little or no material of bacterial origin was present in the haemolysin preparation. These data suggest that alpha-haemolysin may be produced by bacterial modification of a molecule present in meat broth rather than by synthesis de novo within the bacterial cell.