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-co ntrolled smooth change of growth rate was developed. This method was u sed in parallel with batch and chemostat culture techniques for determ ination of the growth characteristics of Escherichia coli K12 on miner al 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 conventi onal chemostat experiment. If in the continuous culture smooth increas e of dilution rate (accelerostat = A-stat cultivation procedure) inste ad of stepwise change was applied, the culture conditions, correspondi ng to the steady state definition, were maintained up to a dilution ra te of 0.47 h(-1). However, at higher dilution rates acetate started to accumulate and growth yield based on glucose consumption decreased. T he 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 ef fect of acetate, accumulating due to the shift up of glucose concentra tion occurring after the stepwise (too sharp) increase of dilution rat e. The continuous cultivation with smooth and constant increase of dil ution rate (A-stat) proved itself as a powerful experimental method fo r the study of the behaviour of growth characteristics.