Growth behaviour and glucoamylase production by Aspergillus niger N402 and a glucoamylase overproducing transformant in recycling culture without a nitrogen source |
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Authors: | J M Schrickx A H Stouthamer H W van Verseveld |
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Institution: | (1) Department of Microbiology, Biological Laboratory, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands |
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Abstract: | When wild-type Aspergillus niger N402 and a glucoamylase-overproducing transformant were grown in recycling culture without a nitrogen source, hyphal tip extension and glucoamylase production still occurred, but overproduction of glucoamylase by the transformant strain stopped. The mycelium retained a low metabolic activity. Light micrographs of mycelial samples showed that some hyphae were broken at their tip and partially empty, while after continuing recycling fermentation for more than 500 h many small and empty pieces of broken mycelium could be found. A model has been developed to calculate the mycelial growth and death rates. The mycelial death rate just exceeded the mycelial growth rate and as a consequence the amount of biomass in the fermentor vessel slightly decreased. It is concluded that the cytoplasmic contents of broken mycelial threads were released into the medium and acted as a nitrogen source for the growing parts of the mycelium. |
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