Selection and characterization of a high alpha-amylase-producing variant in glucose-limited continuous cultures of Aspergillus oryzae

The development and selection of a morphological variant were systematicall y observed during continuous cultures of Aspergillus oryzae A1560 carried o ut at a dilution rate of 0.1 h (1). The selection was monitored by followin g the changes in the population morphology and in the alpha -amylase produc tion during these experiments. A mathematical model for the selection was p roposed assuming that the inoculum consisted of a mixed population. Growth, glucose uptake and alpha -amylase production for the selected morphologica l variant were further investigated in glucose-limited continuous cultures carried out at dilution rates ranging from 0.06 to 0.2 h (1). The selected variant was distinguished from the parental strain in three main aspects: ( 1) a higher capacity of alpha -amylase production at all dilution rates inv estigated; (2) a 36% higher maximum specific growth rate; and (3) a more sp arsely branched mycelium, with fewer aerial hyphae and loss of sporulation ability on solid media.