Characterization of growth and metabolism of Drosophila melanogaster cells transfected with the rabies‐virus glycoprotein gene

In the present study, the growth and key metabolic features of a gene‐transfected Drosophila melanogaster (fruitfly) S2 (Schneider 2) cell population (S2AcRVGP cells), cultured in Sf900‐II medium, have been evaluated to provide substantial support for the development of a bioprocess to produce RVGP (rabies‐virus glycoprotein). Experimental cultures were grown both in a 100 ml Schott flask incubated in a shaker at 28 °C and 100 rev./min and in a 3 litre stirred‐tank bioreactor at 28 °C, with increasing agitation. In small‐scale culture, S2AcRVGP cells reached a maximum cell concentration of 1.13×10 7 cell/ml, presented a μ max (maximum specific growth rate) of 0.037 h −1 and the growth was limited by oxygen deprivation. An early and remarkably long stationary phase was observed under hypoxia. Cell cultures grown in the bioreactor without oxygen limitation exhibited a maximum cell concentration of 2.2×10 7 cells/ml and μ max values as high as 0.048 h −1 . The main substrate consumed in order to reach such a high growth rate was the amino acid proline, which seems to play an important role as a source of metabolic energy in the culture of S2AcRVGP cells. Under conditions of hypoxia, the cells were able to survive for 15 h without apparent damage, recovering their previous metabolic activity.