The stability of an adaptive enzyme formed during growth ofBact. lactis aerogenes (Aerobacter aerogenes)in D-arabinose I. Complex history of the adaptive changes

Abstract

Bact. lactis aerogenesin the early stages of adaptation to use D-arabinose as sole carbon source loses some of its acquired capacity when allowed to go on multiplying in a glucose medium. This is shown by the development of a ‘secondary lag’ on return to D-arabinose. After more prolonged cultivation in D-arabinose the adaptation becomes much more persistent. These effects are correlated with changes in the D-ribulose isomerase activity of broken-up cells (Ab), of intact cells (Aw) and with the rate of degradation of pentose (Ap). IfPis the cell populationAbP,AwPorApPrepresents the total relevant enzyme capacity of the culture. In the very early stages of adaptationAbPfalls rapidly during passage through glucose (AwPandApPmuch less rapidly). After longer exposure to D-arabinose the fall inAbPbecomes less marked. Towards the end of a growth cycle in glucose it rises again. After still further adaptation of the cells to D-arabinose the initial drop inAbPdisappears and the value reached in a glucose medium becomes comparable with that reached in presence of D-arabinose itself. This formation of the enzyme in absence of the ‘inducer’ is correlated with the disappearance of the ‘secondary lag’ in D-arabinose.