BACKGROUND: Poly(beta-malic acid) (PMA) and pullulan are two valuable biopolymers that can be produced simultaneously by certain strains of pullulans. In previous studies, PMA production was successfully improved with reducing pullulan production. In the present study, a DO-shift control strategy was developed to obtain simultaneous high yields of PMA and pullulan. RESULTS: PMA and pullulan co-production at various constant DO levels ranging from 10% to 90% saturation were carried out in a 5 L stirred tank fermentor. Based on the analysis of batch fermentation kinetics at various constant DO levels, a DO-shift control strategy that shifted the DO level from 30% saturation to 70% saturation at 72 h was developed to effectively obtain high productions of both PMA and pullulan. CONCLUSION: By applying the DO-shift control strategy, the maximum concentrations of PMA and pullulan reached 118.6 g L-1 and 27.2 g L-1, respectively. PMA production was successfully improved without sacrificing pullulan production. (C) 2016 Society of Chemical Industry