Observations on nonconverting phage, c-n71, obtained from a nontoxigenic strain of Clostridium botulinum type C.

A nontoxigenic mutant (C-N71) obtained from a toxigenic strain of Clostridium botulinum type C, Stockholm, with nitrosoguanidine treatment was found to be lysogenic by the lysis test. Although the filtrate of a passaged lysate of this nontoxigenic but lysogenic strain, C-N71, lysed cells of the nontoxigenic strain C-AO2 equally as well as the converting phage c-st obtained from the strain C-Stockholm, it did not convert C-AO2 to the toxigenic state. The lysis spectrum of this filtrate was the same as that of the c-st phage. The ability of the filtrate to lyse the indicator cells, C-AO2, was destroyed neither by trypsin nor DNase but was inactivated by heat treatment at 80 C for 10 min. This suggested that the agent which caused lysis was not boticin but probably a phage. An electron micrograph of the complete phage, c-n71, which was similar in morphology to that of the c-st phage was obtained from the filtrate of strain C-N71. Anti-c-n71 phage rabbit serum neutralized both the lytic and the converting activities of the c-st phage. These findings strongly suggest that the c-n71 phage is a mutant of the c-st phage which lacks the gene controlling production of botulinum type C toxin.