The design and characterisation of miniature bioreactors for microbial fermentation process development

This thesis focused on the design and characterisation ofminiature bioreactors and evaluated their potential as a scale-down device for microbial cultivation processes. Miniature bioreactors such as the one detailed in this work have been developed by several research groups and companies and seek to address the current bottleneck at the early stages of bioprocess development. Power input was measured in tW6prototype stirred-tank miniature bioreactors (10 ml and 25 ml) as a function of impeller speed and the vessels were characterised alongside a 7 L bioreactor. The results obtained show that both miniature bioreactors used in this study were able to be characterised using the same methods developed for larger vessels and that the key engineering parameters ofvolumetric oxygen transfer coefficient and mixing time compared favourably with those ofa conventionally-sized bioreactor when expressed as a function ofspecific power input. An Escherichia coli plasmid DNA cultivation was successfully scaled down to the 10 ml miniature bioreactor from a 7 L bioreactor on the basis of equal specific power input, and demonstrated equivalent performance under oxygen-rich and oxygen limited conditions. A batch-fed process to produce a Fab' antibody fragment usingE. coli and a batch cultivation ofthe filamentous bacterium Saccharopolyspora erythraea producing erythromycin were also evaluated in the 25 ml miniature bioreactor and three other small scale cell cultivation devices (i.e. microtitre plate, miniature bubble column reactor and shake flasks). Their relative performances in terms ofgrowth and product formation were related to that ofthe 7 Lbioreactor. The results obtained demonstrated the ability ofthe 25 ml miniature stirred tank bioreactor to perform both ofthese technically-demanding, industrially-relevant bioprocesses to a comparable degree as the 7 L vessel that was not achievable using the other miniature devices tested. The results shown in this thesis highlight the potential of miniature bioreactors to be used to deliver a fully-integrated, high-throughput solution for cell cultivation process development.