In this study, the continuous production of trp promoter-directed interferon-a, using recombinant Escherichia coli, was achieved. The trp promoter was derepressed via the depletion of L-tryptophan in the medium, using casamino acid as an organic nitrogen source. The interferon-of production occurring in this condition was confirmed in a flask culture. A medium for continuous operation was also designed and, using that medium, demonstrated that cell concentration and interferon-alpha production increased proportionally according to glucose concentrations in the reservoir during the continuous culture (dilution rate, D = 0.2 1/h). To examine the optimal condition for continuous production of interferon-a, the continuous operations were carried out at various dilution rates (0. 125, 0.254, 0.32, and 0.41 1/h), in which the glucose concentration in the reservoir was 25 g/L. Stable continuous operation was maintained at D = 0.254 1/h, but only for 51 h. The specific interferon-a production (Y-p/x and specific interferon-a production rates (Q(p)) were estimated at 4.03 +/- 1.23 mg/g and 1.02 +/- 0.31 mg/g/h, respectively. As these values were far lower than those commensurate with high-level expression or high-cell-density cultures, it was inferred that interferon-of was being expressed as a soluble form. In other words, the interferon-a was expressed as a biologically active form within the cytoplasm. Finally, it was concluded that the recombinant interferon-alpha could be produced stably on a continuous basis in this study, in which the trp promoter was derepressed simply by including casamino acid in the culture medium. (c) 2005 Elsevier Ltd. All rights reserved.