METABOLIC-REGULATION IN BACTERIAL CONTINUOUS CULTURES .1

Dilution rate steps in continuous culture experiments with Klebsiella pneumoniae growing on single substrate feeds have brought out interesting features of metabolic regulation not observed in batch cultures. In a step-up experiment, the adjustment of the culture to a new steady state is preceded by an undershoot in cell density. Results of a step-down experiment indicate a corresponding overshoot phenomenon. These observations of the transient behavior of the culture growing on glucose and xylose as well as the steady-state results are interpreted with cybernetic models. The development of the model explicitly accounts for the lumped internal resource, which is optimally allocated toward the synthesis of key enzymes catalyzing different cellular processes. The model also includes a description of the increased maintenance demand observed at low growth rates. It reduces to previous cybernetic models in situations where the cell does not experience a sudden change in its environment and, hence, retains their predictive capability.