The response of a nitrogen‐limited chemostat culture of Escherichia coli B/r to pH and dilution rate steps

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Abstract
The effects of four pH steps and one dilution rate step are described for an ammonia–nitrogen‐limited continuous culture of Escherichia coli B/r. Two of the pH steps, 6.06–5.49 and 5.96–5.60, led to prolonged transients in both cell density and rate‐limiting nutrient concentration. The other two pH steps, 6.20–5.96 and 5.60–6.20, had almost no effect on the culture. The dilution rate step led to a sharp transition in the steady‐state external pyruvate concentration. Monitoring of the external pyruvate concentration for the pH 5.96–5.60 step revealed that the transient phase continued long after the cell density and rate‐limiting nutrient concentration returned to steady‐state values. The implications for industrial and laboratory fermentations are discussed.