The direct fermentation of starch into ethanol by a recombinant Saccharomyces cerevisiae strain YPG/AB, which expresses Bacillus subtilis alpha-amylase and Aspergillus awamori glucoamylase as separately secreted polypeptides, was investigated in both batch and fed-batch fermenter systems under controlled conditions. A 34% increase was observed in ethanol production by YPG/AB in a 40 g l(-1) initial starch containing medium supplemented with 4 g l(-1) glucose. Ethanol productivities were calculated as 0.35, 0.33 and 0.27 g l(-1) h (1) for media with pH 4.5, 5.6 and 6.5, respectively. Substrate controlled fed-batch cultures were used to increase the ethanol production rate. The amount of ethanol produced in fed-batch culture (47.5 g l(-1)) increased by 200% compared to batch culture (15.6 g l (1)). Starch fermentation by S. cerevisiae YPG-AB strain was characterized by ethanol yields/productivities higher than those obtained in comparable fermentations on starch reported in literature. (C) 2002 Elsevier Science Ltd. All rights reserved.