Xanthan gum biosynthesis in a centrifugal, packed-bed reactor (CPBR) was characterized using metabolic flux analysis. Metabolic fluxes through the carbon pathways for xanthan gum production by Xanthomonas campestris were calculated by the metabolic flux-based stoichiometric model. Use of 5.0% instead of 2.5% glucose resulted in an enhanced glucose uptake rate (v(s)) in all bioreactors. The v(s) values in CPBR were significantly higher than those in STR, as were the assembling rate (v(1)) of sugar nucleotides transformed from Glc-6-P. However, the highest ratio of v(1)/v(2) was found in CPBR-LC with 5.0% glucose, indicating that most glucose was utilized for xanthan synthesis with the minimum maintenance requirements in the CPBR-LC operation. Despite the high xanthan productivity and glucose uptake achieved in CPBR-GC, CPBR-LC with 5.0% initial glucose concentration was the most energy-efficient operation among all systems studied. (C) 2003 Elsevier Science Ltd. All rights reserved.