Cells of Clostridium botulinum type A strain 190 grown in thioglycolate medium (GYPT medium) autolysed after having reached a maximum growth. This strain was dissociated into large and small colony-forming types in semisolid media. The cells obtained from the large colony type autolysed more rapidly than those from small one. Washed cells harvested at logarithmic growth phase lysed in phosphate buffer at 37°C within 2-3 hours. Autolysis rose above pH 6.0 and was optimal near pH 7.0. The potential for autolysis reached a maximum toward the end of the logarithmic growth phase and thereafter the cells became resistant to autolysis. The autolytic activity was destreyed by heating the cells at 60°C for 10 minutes and was slightly affected by cysteine (10^-2M), N-ethylmaleimide (10^-2M) and mercaptoethanol (10^-1M).
During autolysis nitrogen, protein, nucleic acids, reducing sugars, amino sugars and botulinum toxin were released from the cells as the reduction of the turbidity in cell suspension occurred. Electron microscopic observations on the process of autolysis revealed that the partial lysis of walls occurred first at the end of the organism and the cytoplasmic contents were lost through such lesions. The lysis of the wall centripetally spread and finally the morphological entity of the wall was completely lost. From these findings it is suggested that the autolysis may be proceded by auto-digestion of the cell wall at the end of the organism.