Studies on induced mutants of Corynebacterium fascians and on their pathogenicity in comparison with that of ‘natural’ strains

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Abstract
SUMMARY: Colony‐type, non‐pigmented and nutritional (auxotrophic) mutants of Corynebacterium fascians were isolated after ultraviolet irradiation of a highly virulent strain. The auxotrophs had single requirements for glycine, aspartic acid, arginine, methionine, creatine or adenine and the amount of their growth in a minimal medium adequate for the parent strain was controlled by the amount of the respective nutrients added.Preliminary results indicated that the pathways by which C. fascians synthesises the substances (with the exception of methionine) required by the mutants were those already known for other micro‐organisms.The induced auxotrophic mutants were examined, in comparison with ‘natural’ or wild strains, for ability to infect sweet pea seedlings and to grow in the environment provided by the host. The mutants were avirulent or weakly virulent unless the specific nutrient was added, and this was correlated with the amount of growth made by the mutants in an aqueous extract of the host tissue. Addition of the specific nutrient improved the growth of the mutant, thus suggesting that avirulence was due, at least in part, to the inability of the pathogen to grow sufficiently in the host environment.