Effect of bacitracin on hGM-CSF production in suspension cultures of transgenic Nicotiana tabacum cells

Bacitracin, a known protease inhibitor, successfully delayed the rate of proteolytic degradation of recombinant human granulocyte-macrophage colony-stimulating factor (hGM-CSF). In transgenic Nicotiana tabacum suspension cell cultures, no growth inhibition was observed when at most 500 mg l−1 bacitracin was added. However, cell growth rate and cell size index were significantly decreased by 1000 mg l−1 bacitracin and the maximum cell concentration was reduced from 17.1 to 11.2 g l−1. In terms of hGM-CSF production, all cultures treated with bacitracin showed improved hGM-CSF production, but the protective effect of bacitracin was diminished in relation to culture time and the decrement of its concentration. Considering both the cell growth and protein production, 500 mg l−1 bacitracin showed the best results and improved the hGM-CSF production to 112.5 μg l−1, which was 2.18-fold higher than the 51.5 μg l−1 of control with no bacitracin. There was no growth retardation or sudden drop in hGM-CSF concentration. The hGM-CSF concentration was increased up to 127.9 μg l−1 with 1000 mg l−1 bacitracin, even though this severely inhibited the cell growth.