Seyed Morteza Robatjazi - Department of Bioscience and Biotechnology, Malek Ashtar University of Technology, Tehran, Iran.
Sanaz Mahboudi - Department of Bioscience and Biotechnology, Malek Ashtar University of Technology, Tehran, Iran.
Mehdi Zeinoddini - Department of Bioscience and Biotechnology, Malek Ashtar University of Technology, Tehran, Iran.

Introduction: Denileukin diftitox is a recombinant immunotoxin composed of truncated diphtheria toxin fused to human interleukin ۲ (DT۳۸۹-IL۲). It is a candidate for protein therapy of lymphoma. This work aims to investigate DT۳۸۹-IL۲ production using a recombinant strain of Escherichia coli in the lab-scale bioreactor. Material and methods: First, the effect of chemical composition in culture medium (the complex and defined) was investigated in DT۳۸۹-IL۲ expression in E.coli BL۲۱ (DE۳) containing pET-IDZ plasmid in shack flask and lab-bioreactor culture. To enrich the carbon source, we added glucose ۶-۸ g/L to the complex culture medium. The composition of the defined medium was enriched by adding amino acids (valine, ۰.۰۵۰۲; phenylalanine, ۰.۰۱۳۲; lysine, ۰.۰۱۸۴; aspartic acid, ۰.۰۱۶; and serine, ۰.۰۲۵۱ g/L). The growth cell was measured by the optical density method and the expression yield was investigated by SDS-PAGE. Results: The maximum growth rate was determined in a modified complex culture medium containing glucose (۶ g/L).  The bacteria growth in the medium was achieved to the optical density of ۵.۵ in the shack flask culture, and under the same condition, the optical density of medium increased to ۱۳ in the bioreactor. Adding amino acids to the defined medium significantly enhanced cell growth and expression of proteins. Also, the optical densities of ۲.۹۵ and ۶.۱ were achieved in the shack-flask and bioreactor culture, respectively. The specific growth rates of bacteria in the complex medium and the defined medium were determined as ۰.۸۹ and ۰.۴۷ h-۱, respectively.  Conclusion: Adding glucose (carbon source) to the complex medium and elemental enrichment by adding amino acids increased biomass production. The growth cell rate in the bioreactor through suitable control of the environmental conditions and proper mixing was higher compared with the shack-flask culture.

Immunotoxin, Denileukin diftitox, Fermentation, Bioreactor