Increased enzyme production under liquid culture conditions in the industrial fungus Aspergillus oryzae by disruption of the genes encoding cell wall-1,3-glucan synthase

Under liquid culture conditions, the hyphae of filamentous fungi aggregate to form pellets, which reduces cell density and fermentation productivity. Previously, we found that loss of -1,3-glucan in the cell wall of the fungus Aspergillus nidulans increased hyphal dispersion. Therefore, here we constructed a mutant of the industrial fungus A. oryzae in which the three genes encoding -1,3-glucan synthase were disrupted (triple). Although the hyphae of the triple mutant were not fully dispersed, the mutant strain did form smaller pellets than the wild-type strain. We next examined enzyme productivity under liquid culture conditions by transforming the cutinase-encoding gene cutL1 into A. oryzae wild-type and the triple mutant (i.e. wild-type-cutL1, triple-cutL1). A. oryzae triple-cutL1 formed smaller hyphal pellets and showed both greater biomass and increased CutL1 productivity compared with wild-type-cutL1, which might be attributable to a decrease in the number of triple-cutL1 cells under anaerobic conditions.