Enhanced cell density cultivation and rapid expression-screening of recombinant Pichia pastoris clones in microscale

Cultivation of yeast Pichia pastoris in the microtiter plate, for optimisation of culture conditions, and expression screening of transformants has gained significance in recent years. However, in the microtiter plate, it has been challenging to attain cell densities similar to well-aerated shake-flask culture, due to the poor mixing resulting in oxygen limitation. To solve this problem, we investigated the influence of multiple cultivation parameters on P. pastoris cell growth, including the architecture of 96-deepwell plate (96-DWP), shaking throw diameter, shaking frequency, culture volume/well, and media composition. In the optimised conditions, a cell density of OD(600) ~50 (dry cell weight ~13 g/L) with >99% cell viability was achieved in the casamino acids supplemented buffered-minimal-media in 300 to 1000 μl culture volume/well. We have devised a simplified method for coating of the culture supernatant on the polystyrene surface for immunoassay. Clones for secretory expression of envelope domain III of dengue virus serotype-1 under the control of inducible and constitutive promoter were screened using the developed method. Described microscale cultivation strategy can be used for rapid high-throughput screening of P. pastoris clones, media optimization, and high-throughput recombinant protein production. The knowledge gained through this work may also be applied, to other suspension cultures, with some modifications.