Effect of hypothermic temperatures on production of rabies virus glycoprotein by recombinant Drosophila melanogaster S2 cells cultured in suspension

Aiming at maximizing the production of transmembrane rabies virus glycoprotein (rRVGP), the influence of hypothermic temperature on a recombinant Drosophila melanogaster S2 cell culture in Sf-900II medium was investigated. Cell growth and rRVGP production were assessed at 4 culture temperatures in Schott flasks: 16, 20, 24 and 28°C. The maximum specific growth rates μ(max) were, respectively: 0.009, 0.019, 0.038 and 0.035h(-1), while the maximum rRVGP levels C(max)(rRVGP) were: 0.075, 2.973, 0.480 and 1.404mgL(-1). The best production temperature (20°C) was then tested in a bioreactor with control of pH and dissolved oxygen in batch and fed-batch modes. In the batch culture, μ(max) and C(max)(rRVGP) were 0.060h(-1) and 0.149mgL(-1) at 28°C and 0.026h(-1) and 0.354mgL(-1) at 20°C, respectively. One batch-culture experiment was carried out with adaptation of the cells by the temperature falling in steps from 20°C to 16°C, so that μ(max) fell from 0.023 to 0.013h(-1), while C(max)(rRVGP) was improved to 0.567mgL(-1). In the fed-batch mode at 20°C, μ(max) was 0.025h(-1) and C(max)(rRVGP) was 1.155mgL(-1). Taken together, these results indicate that the best strategy for optimized rRVGP production is the culture at hypothermic temperature of 20°C, when μ(max) is kept low and with feeding of limitant aminoacids.