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

Abstract

Bact. lactis aerogenes in 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 ( A b ), of intact cells ( A w ) and with the rate of degradation of pentose ( A p ). If P is the cell population A b P , A w P or A p P represents the total relevant enzyme capacity of the culture. In the very early stages of adaptation A b P falls rapidly during passage through glucose ( A w P and A p P much less rapidly). After longer exposure to D-arabinose the fall in A b P becomes 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 in A b P disappears 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.