Multiple beta-fructofuranosidases by Aureobasidium pullulans DSM2404 and their roles in fructooligosaccharide production

At least five types of beta-fructofuranosidases (FFases I, II, III, IV and V) were found in the cell wall of Aureobasidium pullulans DSM2404 grown in a sucrose medium. The fungus first catalyzed the transfructosylation of sucrose, and produced fructooligosaccharide (FOS) and glucose in the culture. FOS was then consumed together with glucose, and finally fructose was produced. In the FOS-producing period, the fungus expressed FFase I as a dominant FFase. However, in the FOS-degrading period, the levels of FFases II, III, IV and V increased. The ratios of transfructosylating activity to hydrolyzing activity by FFases I-V were 14.3, 12.1, 11.7, 1.28 and 8.11, respectively. When glucose was used as a carbon source, only FFase I showed significant activity. On the other hand, the activities of all five FFases were detected when FOS or fructose was used as a carbon source. These results suggested that the expression of FFase I was not repressed by glucose, but those of FFases II-V were strongly inhibited in the presence of glucose. It is considered that FFase I plays a key role in FOS production by this fungus, whereas FFase IV may function as a FOS-degrading enzyme with its strong hydrolyzing activity.