Optimal conditions for alginate production by Azotobacter vinelandii

Abstract

Alginate production from glucose-based media by Azotobacter vinelandii DSM 576 was studied in the shaken-flask scale at different temperatures (23–42°C), shaking speeds (250–450 min −1), and initial concentrations of yields glucose (10–100 g l −1). When buffering the culture medium, alginate ( Y A S ) and bacterial biomass were optimized with respect to the C N ratio and acetate (Ac) and phosphate (Ph) concentrations by performing a composite design experiment. The experimental yields were fitted to the only statistically significant factors with mean percentage errors smaller than 15% and 12%, respectively. The resulting empiric models were used to estimate the C N ratio (110 g-atom C per g-atom N) and concentrations of acetate and phosphate associated with optimum alginate yields ranging from 25 to 33% of the glucose supplied. More specifically, phosphate limitation (0.035 g l −1) and no acetate addition resulted in maximum alginate production with respect to the case of excess of phosphate (3.5 g l −1) and acetate (3 g l −1). Further trials permitted us to assess that the alginate yield was hampered by any sodium acetate addition; however, Y A/X was insensitive to Ph concentrations and C N ratios in the ranges 0.035–1.8 g l −1 and 60–110 g-atom C per g-atom N, respectively, in acetate-free media.