Enhanced production of hyaluronic acid through medium optimization and bioreactor operations in Streptococcus zooepidemicus fermentations

Hyaluronic acid (HA) is a high molecular weight linear polysaccharide, used as a vitreous replacement, eye drop formula and a moisturizer in cosmetic formulations. In order to enhance HA productivity in bioreactor fermentations of Streptococcus zooepidemicus, medium optimization was carried out in the first place. For this purpose, efficient statistical methods were adopted, such as full factorial design (FFD), steepest ascent methods (SAM) followed by response surface methods (RSM). It was observed that the biosynthetic capability of the high-yielding mutants was significantly influenced by the C/N ratio of the production medium in bioreactor fermentations. Sufficient supply of dissolved oxygen through optimization of impeller design and agitation speed rate was found to be another crucial factor for the remarkable enhancement, resulting in approximately 3~4 fold higher HA productivity in 5L batch bioreactor fermentations. Besides, for the purpose of increasing oxygen mass transfer rate (k_La) into the highly viscous fermentation broth caused by very high density of HA, fill and draw mode of bioprocess operation was tested during the course of batch fermentation process. These repeated batch fermentations were carried out by exchanging 50%, 70%, and 90%, respectively, of the HA-containing viscous fermentation broth with fresh production mediums of various compositions.