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 temperatur es (23-42 degrees C), shaking speeds (250-450 min(-1)), and initial co ncentrations of glucose (10-100 g l(-1)). When buffering the culture m edium, alginate (Y-A/S) and bacterial biomass (Y-X/S) yields were opti mized with respect to the C/N ratio and acetate (Ac) and phosphate (Ph ) concentrations by performing a composite design experiment. The expe rimental yields were fitted to the only statistically significant fact ors with mean percentage errors smaller than 15% and 12%, respectively . The resulting empiric models were used to estimate the C/N ratio (11 0 g-atom C per g-atom N) and concentrations of acetate and phosphate a ssociated with optimum alginate yields ranging from 25 to 33% of the g lucose supplied. More specifically, phosphate limitation (0.035 g l(-1 )) and no acetate addition resulted in maximum alginate production wit h 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 y ield was hampered by any sodium acetate addition; however, Y-A/X was i nsensitive 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-fr ee media.