Effect of culture conditions and induction strategies on production of human interleukin-6 by a recombinant Aspergillus nidulans strain

Studies were carried out on factors affecting production of human interleukin-6 (hIL-6) by a recombinant Aspergillus nidulans strain. The expression system included the glucoamylase gene of A. niger and the promoter of the alcA gene. Supplementation of a salts medium, containing fructose and threonine, with acid hydrolysed casein enhanced biomass and hIL-6 production. Addition of the non-metabolisable inducer, cyclopentanone (3 mM) increased hIL-6 production in shake flasks. A maximum hIL-6 titre was observed under these conditions after 45 h. When the process was implemented in a stirred tank fermenter, an optimum titre of 34 mg l(-1) hIL-6 occurred at 36-48 h. Thereafter, a dramatic reduction in hIL-6 activity and in biomass was observed, most likely due to mycelia shearing and protease release. Conditions were established in an air-lift fermenter for production of 54 mg l(-1) hIL-6 after 83 h. A maximum rate of hIL-6 formation of 267 mg l(-1) h(-1) was observed in cyclopentanone induced shake flask cultures.