Continuous cultures for alginate production from Azotobacter vinelandii were conducted at different specific oxygen uptake rates (q(o2)) under oxygen-limited conditions. As a result of varying the agitation rate, the q(o2) increased from 2.2 to 6.0 mmol g(-1) h(-1). An increase in q(o2) up to 4.8 mmol g(-1) h(-1) resulted in an increase of alginate concentration, as well as in the specific alginate production rate, which can be attributed to that carbon flux was less diverted towards biomass production. A lower alginate molecular weight (869 kDa as compared to 1350 kDa) was obtained by increasing the q(o2) from 2.2 to 4.8 mmol g(-1) h(-1) and a higher gene expression of algL (about 8-fold) was observed, which could explain the decrease in the alginate molecular weight. The results showed for the first time that alginate production and carbon distribution are affected by the q(o2). The manipulation of this parameter could be used as a control strategy for alginate production. (C) 2011 Elsevier Ltd. All rights reserved.