Manipulating the molecular weight of alginate produced by Azotobacter vinelandii in continuous cultures

Alginate production by Azotobacter vinelandii in chemostat cultures was evaluated at different dilution rates (D) and inlet sucrose concentrations of 5 and 20 g l−1. At the low inlet sucrose concentration, the molecular weight of alginate increased from 800 to 1800 kDa when D increased from 0.05 to 0.10 h−1, whereas the opposite trend was observed with the high inlet sucrose concentration. This behaviour can be explained by changes in specific sucrose uptake rate. Thus, a decrease in alginate molecular weight was dependent on the specific sucrose uptake rate when this rate was higher than 0.42 g g−1 h−1. The manipulation of the D can be used to select the molecular weight of alginate in continuous culture.