OPTIMAL CONDITIONS FOR ALGINATE PRODUCTION BY AZOTOBACTER-VINELANDII

Alginate production from glucose-based media by Azotobacter vinelandii DSM 576 was studied in the shaken-flask scale at different temperatures (23-42 degrees C), shaking speeds (250-450 min(-1)), and initial concentrations of glucose (10-100 g l(-1)). When buffering the culture medium, alginate (Y-A/S) and bacterial biomass (Y-X/S) yields 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.