Fig. 6

Fed-batch cultivation of T. reesei RutC30. A Scattered light, B DO and feed over time. The line graph presents the mean of the replicates, while the colored areas surrounding the line illustrate the standard deviation. C pictures taken from the bottom of the cultivation plate at the end of cultivation, D offline measurement of cellulase activities for batch and fed-batch cultivations using the same overall carbon sources (2.5 g l\(^{-1}\) glucose and 16.6 g l\(^{-1}\) lactose). The DO shows that the feeding rates were appropriately chosen to cover the range from limiting to high substrate feeding. The highest feeding rate of 0.75 g (l h)\(^{-1}\), which was overfed based on the DO, led to low cellulase activities, similar to batch cultivations with identical concentrations of glucose and lactose. In contrast, for the feeding rates of 0.3 g (l h)\(^{-1}\), 0.45 g (l h)\(^{-1}\) and 0.6 g (l h)\(^{-1}\), which are assumed to be carbon limited, only the lowest feeding rate of 0.3 g (l h)\(^{-1}\) revealed a significant increase in cellulase activities compared to the other conditions. Specifically, there was a threefold increase in cellobiohydrolase and a fivefold increase in \(\upbeta\)-glucosidase activity compared to the batch conditions. Notably, a morphological change to a combination of microfilamentous structures and pellets was observed in the fed-batch cultivation. Cultivation conditions: Microfluidic RWP, adapted medium, n = 1000 rpm, \({\text{d}_{0}}=3\) mm, \({\text{V}_\text{W}}=3.4\) ml, \({\text{V}_\text{L}}=1\) ml, humidity \(\ge 85\)%, \({\text{O}}_2=35\)%, T = 30 \(^\circ\)C, inoculum = 10\(^{5}\) spores ml\(^{-1}\), batch: 2.5 g l\(^{-1}\) glucose, fed-batch: 16.6 g l\(^{-1}\) lactose as constant feed with a feeding rate of 0.30, 0.45, 0.60 or 0.75 g (l h)\(^{-1}\)