Abstract
In the case of a wild-strain of E. coli ATCC 9637,the concentration of thiamine-thiazole required to reverse inhibition showed a competitive relationship with the concentration of "amino-thiazole" present in a minimal medium. The growth of a mutant 70-23,which requires pre-formed thiamine, was not appreciably, inhibited by amino-thiazole under the condition which permitted its growth to a limited extent. The mutant 26-43,whose genetic deficiency is characterized as an inability of carrying out thiazole synthesis while its synthetic ability of thiamine in the conjugation of pyrimidine and thiazole is retained as well as in the wild-strain, was slightly more susceptible to amino-thiazole than the wild-strain. Among thiamine-requiring strains, 70-17 which was previously indicated to have been blocked partially in the conjugation of the two moieties of thiamine, was nhibited by the lowest level of amino-thiazole. For securing particular classes of auxotrophs from a wild-strain, it is most important that nutrients excreted from prototrophs are not utilized by auxotrophs during penicillin screening. Isolation of thiamine-requiring mutants, partially blocked in the reaction for thiamine synthesis was easily permitted by a selection in a penicillin medium containing a certain concentration of amino-thiazole. This success may be due to the avoidance of syntrophic sterilization of desired type of mutants by the presence of the anti-metabolite, to which the mutant is more susceptible than the parent organism.
