Development of a cell-loaded biosupport separator for continuous immobilized-cell perfusion culture

An efficient cell-loaded biosupport separator of the decantor type was developed and applied for a continuous perfusion culture to produce cyclosporin A (CyA), in which fungal cells were immobilized on Celite beads. In the preliminary experiments employing highly viscous polymer (carboxymethyl cellulose) solutions, the decantor showed good separation performances at high solution viscosites and dilution rates. Two concentric cylindrical tubes installed inside the decantor turned out to play key roles in the efficient separation of the immobilized cells. By installing the decantor on an immobilized-cell perfusion bioprocess system, a stable continuous operation was possible even at a high dilution rate for an extended period, leading to high productivities of free cells and CyA. Almost no immobilized biomass existed in the effluent stream from the bioreactor, demonstrating the effectiveness of the decantor system. It is noteworthy that we could obtain these results despite unfavorable fermentation conditions, i.e., reduced apparent density of cell-loaded beads and increased drag force on the bead particles caused by overgrowth of cells on the bead surface, tubulence caused by large air bubbles, and the existence of a high density of suspended fungal cells (10 g/L) in the fermentation broth.