In all other 2-l fermentations, the glucose concentration was controlled manually. The fermentations were started as batch process with 38 g l−1 glucose. When the concentration decreased to a value between 0.5 and 1 g l−1, feeding was started. The concentration was controlled to 0.7 g l−1 by adjusting the glucose pump rate manually, according to glucose measuring stripes. Feed in fed-batch-process in all fermentations was a highly concentrated glucose solution (636 g l−1).
In contrast to the laboratory dialysis fermenter, where dialysis is working right from the beginning, dialysis with external modules was started at cell densities of 10 g l−1. Previously, the fermentation was performed in fed-batch mode.
In all dialysis fermentations with protein expression, the addition of IPTG into the fermenter at a cell density of 40 g l−1 was used for induction. Optimal cell density for IPTG addition had been determined earlier in the laboratory dialysis fermenter. 3. Results