The influence of aeration on the fermentation of a mixture of glucose and xylose by the naturally xylose fermenting fungus Fusarium oxysporum was studied in batch cultivations. The aeration level had considerable influence on the co-metabolism of glucose and xylose. Under anaerobic conditions xylose consumption was limited and xylitol was the main product of xylose metabolism. When the artificial electron acceptor acetoin was added xylose consumption increased by 95% with a significant improvement of ethanol yield from 0.96 to 1.52 mol/mol, mainly due to a 72% reduction of xylitol excretion. The profile of the phosphorylated intermediates during the fermentation suggests that a high glycolytic flux occurred during the oxygen-limited conditions, characterized by high efflux of glyceraldehyde-3-P (G3P) and fructose-6-P (F6P) from Pentose Phosphate Pathway (PPP) to Embden-Meyerhof-Parnas Pathway (EMP) resulting in the higher ethanol production. An accumulation of sedoheptulose-7-P (S7P) was also observed indicating a block in the PPP which affects the production of NADPH and results in the production of acetate and the reduced xylose consumption. (C) 2004 Elsevier Inc. All rights reserved.