Optimisation of a recombinant Hepatitis B vaccine through the cultivation and fermentation of Aspergillus Niger
Date
2005-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The development of non-replicating vaccines is an emerging option for safe, effective
vaccines, several of which contain virus-like particles (VLPs). Many recombinant
expression systems have been evaluated as hosts for VLP production for the prevention
of infectious diseases. The filamentous fungi Aspergillus niger has emerged as a
potential alternative expression system for cost effective VLP vaccine production.
Hepatitis B surface antigen (HBsAg) was used as a model VLP product to benchmark
A. niger’s production capacity with those of Saccharomyces cerevisiae, Pichia pastoris
and Hansenula polymorpha. Bioprocessing strategies were used to optimise VLP
production by recombinant A. niger in batch culture. In particular, the effect of the
parameters culture temperature, inoculum concentration, agitation intensity, dissolved
oxygen (dO2) concentration and culture pH on biomass formation, morphology and
VLP (HBsAg) production concentration was quantified. At an optimum agitation of
100 rpm and optimum dO2 concentration of 50 %, HBsAg production levels were
increased 9-fold compared to yields obtained in shakeflask cultivation. Highest HBsAg
production levels of 3.6 mg.ℓculture
-1 and 350 μg.gDW
-1 were recorded, at a biomass
concentration of 10.5 gDW.ℓculture
-1. These production levels compare favourable with
those obtained by other production systems under similar conditions. HBsAg VLPs
mostly accumulated intracellularly, although under optimum bioreactor conditions
significant HBsAg accumulation in the cytoplasm and culture supernatant was also
observed. The impact of these process parameters on VLP production and cell
morphology was attributed to environmental stress conditions. Volumetric biomass and
HBsAg production levels were maximised under conditions of lowest environmental
stress, resulting in the most optimal small-pelleted morphology. These results indicate a
substantial potential for further engineering of the A. niger production system for the
high level of intracellular and extracellular VLP production.
Description
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005.
Keywords
Dissertations -- Process engineering, Theses -- Process engineering, Hepatitis B vaccine, Aspergillus niger, Biochemical engineering, Hepatitis B