When cultivated in double strength SC-URA medium with 20 g l-1 glucose under aerobic conditions, the extracellular α-amylase activities were similar for S. cerevisiae Y294[AmyA] and Mnuα1[AmyA] (Figure 4a). However, the glucoamylase activity in the supernatant from S. cerevisiae Mnuα1[GlaA] was significantly higher than that of S. cerevisiae Y294[GlaA] (Figure 4b), which could be ascribed to a potentially better secretion ability of S. cerevisiae Mnuα1. Furthermore, co-production of AmyA and GlaA resulted in lower levels of both activities compared to those observed for the individual enzymes. Similar results were observed for the separate and co-expression of a xylanase and xylosidase in S. cerevisiae Y294 [34] and could be ascribed to a number of reasons that were not further investigated in this study.