Scale-down and parallel operation of the riboflavin production process with Bacillus subtilis

The establishment and the improvement of industrial bioprocesses calls for the selection of media compositions and process conditions in highly parallel experiments as well as for the intensified screening of new biocatalysts and improved production strains. This work presents for the first time the scale-down and the successful adaptation of an industrial riboflavin fed-batch production process with Bacillus subtilis to a fully automated setup with 48 parallel stirred bioreactors at a milliliter scale (10 mL). The feasibility of an intermittent feeding mode and a discontinuous at-line pH control for parallel cultivations over up to 53 h is demonstrated together with interlaced process analyses at a microliter scale for quasi-simultaneous at-line monitoring of biomass, substrate and product concentration. The discontinuous feeding mode necessitated an increased oxygen input, resulting in lower final biomass concentrations. However, the product yields and volumetric productivities in the milliliter setup were equivalent to the yields and productivities obtained during the reference cultivations at laboratory scale, which allows considering the automated system together with the developed schedule as a screening tool for high-throughput bioprocess design of the described production process.