Nature and Properties of a Cytolytic Agent Produced by Bacillus subtilis

Surmmary The substance responsible for lysis of erythrocytes by cultures of Bacillus subtilis, designated subtilysin, was purified. It contained a peptide of leucine, aspartic acid, glutamic acid and valine and probably a lipid. Subtilysin was activated by Mg2+, Mn2+ and Ca2+. The rate of haemolysis was abruptly increased by chilling the reaction mixture. Haemolysis was inhibited by normal sera; the most inhibitory serum fractions contained α-and β-globulins. Haemolysis was inhibited by low concentrations of phosphatidylcholine, phosphatidylinositol, phosphatidic acid and sphingomyelin. Subtilysin possessed antibiotic properties and lysed protoplasts and spheroplasts derived from several bacterial species; subtilysin was identical with surfactin, a peptidelipid from B. subtilis cultures that inhibits fibrin clot formation. Kakinuma and co-workers found surfactin to be a heptapeptide having an n-terminal glutamic acid in amide linkage with the carboxyl group of 3-hydroxy-13-methyl-tetradecanoic acid. Surfactin (subtilysin) possesses some properties in common with two other cytolytic agents of bacterial origin, namely, staphylococcal η-toxin and streptolysin S.