GROWTH-BEHAVIOR AND GLUCOAMYLASE PRODUCTION BY ASPERGILLUS-NIGER N402AND A GLUCOAMYLASE OVERPRODUCING TRANSFORMANT IN RECYCLING CULTURE WITHOUT A NITROGEN-SOURCE

When wild-type Aspergillus niger N402 and a glucoamylase-overproducing transformant were grown in recycling culture without a nitrogen sourc e, hyphal tip extension and glucoamylase production still occurred, bu t overproduction of glucoamylase by the transformant strain stopped. T he mycelium retained a low metabolic activity. Light micrographs of my celial samples showed that some hyphae were broken at their tip and pa rtially empty, while after continuing recycling fermentation for more than 500 h many small and empty pieces of broken mycelium could be fou nd. A model has been developed to calculate the mycelial growth and de ath rates. The mycelial death rate just exceeded the mycelial growth r ate and as a consequence the amount of biomass in the fermenter vessel slightly decreased. It is concluded that the cytoplasmic contents of broken mycelial threads were released into the medium and acted as a n itrogen source for the growing parts of the mycelium.