Observations on Nonconverting Phage, c‐n71, Obtained from a Nontoxigenic Strain of Clostridium botulinum Type C

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Abstract
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.