The influence of nitrogen sources on the α-amylase productivity of Aspergillus oryzae in continuous cultures

Abstract

The influence of the nitrogen source on the α-amylase productivity of Aspergillus oryzae was quantified in continuous cultivations. Both inorganic and complex nitrogen sources were investigated and glucose was used as the carbon and energy sources. For production of α-amylase, nitrate was shown to be inferior to ammonia as a nitrogen source. A mixture of ammonia and complex nitrogen sources, such as yeast extract or casein hydrolysate, was better than with ammonia as the sole nitrogen source. Even a low concentration of casein hydrolysate (0.05 g l⁻¹) resulted in a 35% increase in the α-amylase productivity. The higher α-amylase productivity during growth on casein hydrolysate was not caused by increased transcription of the α-amylase genes but was caused by a faster secretion of α-amylase or by a lower binding of α-amylase to the biomass.