EXPRESSION OF Pisum sativum DEFENSIN 1 (Psd1) IN SHAKING FLASKS AND BIOREACTOR CULTIVATIONS OF RECOMBINANT Pichia pastoris AT DIFFERENT pHs

The methylotrophic yeast Pichia pastoris was used to produce the recombinant Pisum sativum defensin (rPsd1), a small peptide from pea seeds that has a high level of antifungal activity. The plasmid rPsd1/pPIC9 was integrated into the yeast genome and methanol was used to induce expression and secretion of the recombinant Psd1, at 30 C in a fed-batch mode. The effects of different pH conditions and process scale-up were evaluated using a Monod-type model where dissolved oxygen was considered the limiting substrate. Parameter estimation showed that the process could be improved by expressing rPsd1 in a 1000 mL bioreactor at pH 4. Structural and functional analyses revealed that the recombinant Psd1 is very similar to the native one.