The computer-controlled continuous culture of Escherichia coli with smooth change of dilution rate (A-stat)

A method of continuous cultivation of bacterial cells with computer-controlled smooth change of growth rate was developed. This method was used in parallel with batch and chemostat culture techniques for determination of the growth characteristics of Escherichia coli K12 on mineral salt medium with glucose. The maximum growth rate (0.5-0.55 h(-1)) for this strain determined in the batch culture was remarkably higher than the wash-out value (mu(wa) = 0.38 h(-1)) observed in the conventional chemostat experiment. If in the continuous culture smooth increase of dilution rate (accelerostat = A-stat cultivation procedure) instead of stepwise change was applied, the culture conditions, corresponding to the steady state definition, were maintained up to a dilution rate of 0.47 h(-1). However, at higher dilution rates acetate started to accumulate and growth yield based on glucose consumption decreased. The maximum growth rate mu(max) observed in these experiments was 0.57 h(-1). The wash out of the culture at relatively low dilution rate (D = 0.38 h(-1)) in the chemostat could be explained by the inhibitory effect of acetate, accumulating due to the shift up of glucose concentration occurring after the stepwise (too sharp) increase of dilution rate. The continuous cultivation with smooth and constant increase of dilution rate (A-stat) proved itself as a powerful experimental method for the study of the behaviour of growth characteristics.