Change in hyphal morphology of Aspergillus oryzae during fed-batch cultivation
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Industrial enzymes are often produced by filamentous fungi in fed-batch cultivations. During cultivation, the different morphological forms displayed by the fungi have an impact on the overall production. The morphology of a recombinant lipase producing Aspergillus oryzae strain was investigated during fed-batch cultivations. During the exponential batch phase of the fed-batch cultivations, the average hyphal length increased as did the number of tips per hyphal element. Most striking was the finding that the diameter of the hyphal elements increased with an average factor of 1.5 during the batch phase from 2.8–2.9 up to 4.0–4.4 μm. The diameter of the hyphal elements remained constant, around 4 μm, after the feed was started. However, the diameter of the immediate hyphal tip, where the enzyme secretion is thought to take place, increased dramatically with up to a factor 2.5 during the feeding period. The expression of the recombinant lipase was induced by the feeding with maltose, and an increase in lipase activity was seen in parallel to a swelling of the tips. The results indicate that the two events are linked as a return to normal growth was observed upon cessation of production due to oxygen limitations.
KeywordsLipase Specific Growth Rate Aspergillus Oryzae Stirrer Speed Batch Phase
DELTA, Denmark, has provided us with the BioView for which we are grateful, and especially the technical support and suggestions from Carsten Lindemann is greatly appreciated. We would also like to thank Professor Jens Nielsen for fruitful discussions and comments on the manuscript. This research was performed within the framework of Center for Combination of Sensors, which was financed by the Danish Agency for Trade and Industry, Contract no. 1999-603/4020-3.
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