Shaken flasks by resonant acoustic mixing in the biosynthesis of alginate by Azotobacter vinelandii with non‐Newtonian rheological characteristics

BACKGROUND: Orbitally shaken flasks in polysaccharide-producing bacterial cultures usually present oxygen limitations because of non-Newtonian rheological characteristics of the resulting culture broth and bacterial respiration. Here, we present the production of alginate by Azotobacter vinelandii using a novel alternative mixing technology (resonant acoustic mixing, RAM) to increase oxygen transfer. RESULTS: No significant differences were observed in biomass growth (3.43 +/- 0.61 g L-1) with RAM frequencies between 5 and 20 g, but higher specific growth and sucrose consumption rates were found at higher frequencies (15 and 20 g). The highest alginate production (9.13 +/- 0.63 g L-1) was obtained in 20 g cultures, in which no oxygen limitation was detected, whereas intracellular reserve polymer poly-beta-hydroxybutyrate (PHB) production was favored at low shaking frequencies (5 and 10 g), in which dissolved oxygen tension was zero for a long culture time. Cultures behave pseudoplastically, with an apparent viscosity that increases until the end of the exponential phase, and the alginate monomer ratio was approximately 1.0 in all cultures. CONCLUSION: RAM can maintain elevated oxygen transfer rates, even in non-Newtonian high-viscosity cultures, as in the case of alginate production by A. vinelandii. (C) 2017 Society of Chemical Industry