Modeling of enzyme-mediated glucose release to facilitate continuous feed in miniaturized cultivations

When striving for maximal throughput at minimal volumes while cultivating close to industrial conditions, simple and robust feeding strategies offer important advantages. Enzyme-mediated glucose cleavage from dextrin is an easy way of imitating continuous fed-batch in the small scale, with no complex equipment required. While the release rate - and thus the feed rate - can be controlled by adapting the enzyme concentration, it strongly depends on the concentration of the involved substances and the environmental conditions. Thus, it is a challenge to use the technology for controlling the specific growth rate, as it is commonly done with feed pumps. For solving this problem, we present here a mathematical model that extends simple Michaelis-Menten kinetics by considering different substrate fractions and can be applied to control the glucose release rate even in high throughput experiments. The fitted model was used during automated microbial cultivations to control the growth rate in quasi-continuous fed-batch processes and to realize different exponential growth rates by intermittent additions of enzyme and dextrin by a liquid handling robot system. We thus present an approach for defined biocatalytically controlled glucose supply of small-scale systems, where - if at all - continuous feeding was only possible with low accuracy or high technical efforts until now.