Loss of Aspergillus oryzae amyR function indirectly affects hemicellulolytic and cellulolytic enzyme production

Aspergillus oryzae AB390, a derivative of A. oryzae OR101, was found to be suitable for soy sauce production, yielding a product light brown in color. Compared to the parent strain, hemicellulase and cellulase activities in the mutant were higher; however, its amylase activity was found to be much lower. To determine the cause of these differences, the enzymatic profile change, as a function of the carbon source in submerged cultures, was examined. Amylase activity in AB390 was hardly detectable and not affected by the carbon source utilized. In the absence of starch where glucose could not be generated, hemicellulase and cellulase activities in both the parent and mutant were the same. A nonsense mutation was found in the upstream region of the putative transactivation domain of the transcriptional activator of the amylolytic genes, amyR in AB390. Complementation of AB390 with the wild-type amyR reduced hemicellulase and cellulase activities and increased amylase activity in soy sauce koji, the mold responsible for giving soy sauce. Northern analysis and two-dimensional (2-D) electrophoresis indicated that the unique enzymatic profile of AB390 was regulated transcriptionally. The results suggested that the loss of amyR function indirectly affected the production of hemicellulolytic and cellulolytic enzymes, likely through a carbon catabolite repression-mediated control.