Reproducing shake flasks performance in stirred fermentors: production of alginates by Azotobacter vinelandii.

Keeping equal the initial power drawn (0.27 W l(-1)) in shake flasks and in a stirred fermentor did not reproduce the behaviour of alginate production by Azotobacter vinelandii. A lower mean molecular weight (1.1x10(6) Da) of the polymer was obtained in the bioreactor as compared to that obtained in shake flasks (1.9x10(6) Da). The reasons for this can reside in the fact that the evolution of the power drawn in the shake flasks could be considerably different to that observed in the stirred bioreactor. A drastic drop in the specific power drawn is expected in the shake flasks as a consequence of the increased viscosity, which caused the liquid not following the movement of the shaker. This was supported by the fact that cultures developed in the fermentor at lower initial power drawn (as low as 0.027-0.056 W l(-1)) or in a culture in which the power drawn was deliberately reduced along cultivation, produced alginates with similar molecular characteristics as that obtained in shake flasks.