Optimization and scalable production of Corynebacterium diphtheriae toxin using an animal component free medium: a...

Diphtheria is an infectious disease causing severe illness, particularly in children, which can be prevented by vaccination with diphtheria toxoid, a detoxified derivative form of diphtheria toxin. The present study aimed to overcome the limitations of traditional animal-derived medium and to enhance diphtheria toxin production by refining the various process parameters and iron concentration of semi-synthetic medium. The iron concentration in the medium was investigated in the range of 0.05 to 0.6 µg/mL, and an ideal concentration was found to be 0.4 µg/mL, where 221 ± 7.6 Lf/mL of DT was obtained. Response Surface Methodology was used to further optimize physical parameters such as pH, temperature, agitation speed, and concentration of inoculum. A central composite design comprising 30 experimental runs identified the best conditions as pH 7.2, temperature 35 °C, agitation speed 150 rpm, and 5.8% inoculum concentration yielding a maximum DT yield of 245 ± 5 Lf/mL. To validate scalability, a 5 L stirred-tank bioreactor was used to assess the influence of aeration and agitation on biomass and diphtheria toxin production were studied. At 600 rpm and 0.25 VVM, a maximum of 266 Lf/mL of diphtheria toxin was obtained. The biomass and toxin yields were adversely affected by higher aeration and agitation. This study highlights the significance of optimizing process parameters and establishing a scalable strategy for efficient production of diphtheria toxin using animal component-free medium.