Continuous pullulan fermentation in a PCS biofilm reactor

Biofilms are natural form of cell immobilization in which microorganisms attach onto solid support. In this study, a pigment-reduced pullulan-producing strain, Aureobasidium pullulans (ATCC 201253), was used for continuous pullulan fermentation in a Plastic Composite Support (PCS) biofilm reactor. Optimal conditions for the continuous pullulan production were determined by evaluating the effects of the feeding medium (concentrations of ammonium sulfate and sucrose) and dilution rate. Pullulan concentration and production rate reached maximum (8.3 g/l and 1.33 g/l/h) when 15 g/l of sucrose, 0.9 g/l of ammonium sulfate and 0.4 g/l of yeast extract were applied in the medium, and the dilution rate was at 0.16 h^-1. For system stability evaluation, A. pullulans produced equal amount of pullulan after 60 residence times, and the purity of produced pullulan was 93.0%. The ratio of hyphal form cells on the PCS increased since the solid support is more suitable for the attachment of filamentous cells. Overall, the increased pullulan productivity can be achieved through biomass retention by using PCS biofilm reactor.