The Consequences of Mutation during the Growth of Biochemical Mutants of Escherichia coli

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Abstract
During the growth of population of histidineless E. coli, mutations occur which make some of the bacteria independent of an external supply of histidine. These histidine-independent mutants grow in the absence of added histidine and such growth from an inoculum of histidineless bacteria is termed adaptation. The extent to which adaptation occurs is inversely proportional to the histidine content of the medium. On high concns. adaptation does not take place. As a result there is a dip in the curve describing adaptive growth as a function of histidine concn. This dip can be progressively eliminated by adding histidine-independent bacteria which artificially decreases the proportion .of histidineless bacteria in the inoculum. Pure histidine-independent cultures show no dip in the curve, for their growth is not influenced by histidine in the medium. The depression of adaptation is a function of the number of histidineless bacteria present. As the histidine concentration increases, the number of histidineless organisms whose growth is supported increases, and the adaptative growth of histidine-independent mutants decreases. The latter are in some way prevented from growing by histidineless bacteria grown on sub-optimal concns. of histidine.