The adaptation of Bact. lactis aerogenes and Bact. coli mutabile to various carbohydrates

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Abstract
A study was made of the adaptation of Bacterium lactis aerogenes (1) and of Bact. coli mutabile (2) to artificial media containing various carbon sources, and of the subsequent loss of this adaptation. As measured by the growth rate of successive subcultures, adaptation of (1) transferred from glucose to lactose, maltose and sucrose is usually complete after two or three passages, the final growth rate of trained cells being the same as that in glucose. There is, however, evidence that the adaptation does not consist simply in the development of a hydrolytic enzyme which produces glucose from the disaccharides. Cells trained to lactose, maltose or sucrose, respectively, do not grow at the optimum rate in the other 2 sugars, though by training in successive stages, cells fully adapted to all 3 sugars can be produced. All these strains grow from the start at the opt. rate in cellobiose and cells transferred from glucose grow normally in galactose. The behavior of (2) differs from that of (1) only in degree, the most marked differences being an exceptionally long lag on the first subculture in lactose and inability to grow in sucrose or cellobiose. The subsequent course of the adaptation to lactose closely resembles that of the aerogenes strain. The extent to which the lactose-adaptation of (1) is lost when the cells are grown in glucose once more depends upon the length of time for which the training has been in effect. When the cells are just fully trained, reversion occurs readily, but, after fuller training, its onset shows a well-marked delay. Finally the trained strain becomes completely stable, but before this stage is reached the cells will suffer an induced reversion if grown in the presence of maltose (though many other agents are quite without effect). The facts about the development and loss of adaptation are difficult to explain except by a theory postulating specific modification of the enzymes of all the cells (as distinct from a natural selection of suitable cells), and certain aspects of the behavior may be understood in the light of analogies beteeen the expansion of cell substance and the growth of crystal lattices. Certain modifications in current views about Bact. coli mutabile are suggested in view of the similarities between its behavior and that of Bact. lactis aerogenes.

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