Variations in ribulose isomerase activity and the rate of pentose disappearance during adaptation of Bact . lactis aerogenes to D-arabinose

Abstract

The variation of ribulose isomerase activity in strains of Baceterium lactis aerogenes, during adaptation to D-arabinose, has been studied in both intact and broken cell preparations in the lag phase and the first growth cycle. Small quantities of enzyme activity were detected in unadapted cells grown in glucose, increasing more than 100-fold when the cells were adapted. The pattern of increasing ribulose isomerase activity in intact cells during the earliest stages of observable division was studied, and was found to differ markedly from the pattern to be expected from the assumption that mutation and selection are responsible for the adaptive response. The variation in the apparent activity of the cells in artificial mixtures of adapted and unadapted organisms was found to approximate to the behaviour expected for the selection of pre-adapted cells in D-arabinose media. These results were confirmed by parallel measurements on the rate of consumption of the pentose by the bacteria. Changes in cell permeability concomitant with the development of the adaptive enzymes were also followed during the lag phase and first growth cycle in D-arabinose. Serial subcultures in D-arabinose media were carried out to determine the effect of training on the maximum intact cell enzyme activity in a given culture and on the corresponding mean generation time. An explanation of the results obtained, in terms of the adaptation of the majority of the cells inoculated into a D-arabinose medium is discussed.