BACKGROUNDThe yeast Pichia pastoris is widely used as a production platform for secreted recombinant protein. The application of oxygen-limiting conditions leads to an important increase in protein specific productivity driven by the GAP promoter. RESULTSThe physiological and metabolic adaptation of the host to a wide range of oxygen availability has been systematically studied in glucose-limited chemostat cultivations producing an antibody fragment (Fab). A weighty increase of up to 3-fold of the specific Fab production rate (q(Fab)) and Fab yield (Y-PX) has been achieved for the optimal conditions. Besides the remarkable increase on both Fab yield and productivity, as a consequence of the metabolic shift from respiratory to respiro-fermentative pathways, a decrease on biomass yield and generation of several secreted by-products have been observed. CONCLUSIONThe accurate system characterization achieved throughout the bioprocess specific rates and the monitoring of cell physiology allowed the determination of the optimal conditions to enhance bioprocess efficiency. This work also presents a versatile approach based on the physiological state of the yeast that can be used to implement the desired oxygen-limiting conditions to fermentations set-ups with different oxygen transfer capacities, alternative operating modes, and even for the production of other proteins of interest. (c) 2017 Society of Chemical Industry