Increased hepatitis B surface antigen production by recombinant Aspergillus niger through the optimization of agitation and dissolved oxygen concentration
The capacity of the filamentous fungi Aspergillus niger to produce and assemble complex immunogenic viral proteins into virus-like particles (VLPs) in batch culture was enhanced by optimizing the bioprocessing parameters, agitation intensity and dissolved oxygen (dO2) concentration. Response surface methodology (RSM) and a two-factor-two-level central composite rotatable design (CCRD) were employed to evaluate the interactive response pattern between parameters and their optimum combination. The recombinant hepatitis B surface antigen (HBsAg) was used as a model VLP system to determine the effect of these parameters on biomass yield, fungal morphology, HBsAg production and bioreactor kinetics. The response surface model predicted optimum cultivation conditions at an agitation of rate of 100 rpm and a dO2 concentration of 25%, obtaining highest intracellular membrane-associated HBsAg levels of 3.4 mg lculture-1. HBsAg production levels were increased tenfold compared to yields obtained in shake flask cultivation. Although hepatitis B VLPs mostly accumulated intracellularly, optimal bioreactor conditions resulted in significant HBsAg release in culture supernatant. These results compare favourably with other recombinant VLP systems in batch culture, and therefore, indicate a substantial potential for further engineering of the A. niger production system for the high level of intracellular and extracellular VLP production. © 2007 Springer-Verlag.