Morphology and physiology of an α-amylase producing strain of Aspergillus oryzae during batch cultivations

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Abstract
The microscopic morphology, that is, total hyphal length and total number of tips, has been characterized during batch cultivations of Aspergillus oryzae. The specific growth rate estimated by measuring the total hyphal length (μh) corresponds well with the specific growth rate estimated from dry weight measurements during cultures grown as free hyphal elements. The average tip extension rate can be described with a saturation type kinetics with respect to the average total hyphal length, and the branching frequency is closely related to the total hyphal length. For the applied strain of A. oryzae, pellet formation occurs by coagulation of spores. The agglomeration process is pH dependent and pellets are formed at pH values higher than 5, whereas low pH (k in the cube-root law is derived from the growth kinetics with no mass transfer limitation, k = μh/3. Based on an oxygen balance, the active growth layer in the pellet is estimated to be 200 to 325 μm and, consequently, up to 50% of the biomass is limited by oxygen for large pellets. Ethanol production (up to 1 g L−1) was observed during batch cultivations with pellets, suggesting that ethanol is produced in the oxygen limited part of the biomass. A constitutive, low α-amylase production was observed at high glucose concentration. The specific α-amylase production was significantly higher for filamentous growth than for pellets and oxygen appears to be necessary for production of α-amylase. © 1996 John Wiley & Sons, Inc.