Abstract
Aspergillus nidulans cultures did not produce penicillin when growing in the pelleted form (1-5mm in diameter) but production was observed in cultures growing as micropellets or completely a filamentous morphology. The Adenylate Energy Charge (A.E.C.) and Oxygen Uptake Rates (O.U.R.) were measured in cultures with the three morphological states, and it was shown that both were lowest during pelleted growth and highest during filamentous growth. It was therefore proposed that the oxygen limitation, and the subsequent physiological consequences of pelleted morphology, inhibited growth and primary metabolism and hence inhibited secondary metabolism. Investigations into the effect of growth rate were carried out and it was observed that a down regulation of growth rate induced secondary metabolism regardless of the type of growth rate limiting nutrient. An exception to this was oxygen limitation which did not support production. The distribution of pellet sizes was calculated for the pelleted population and it was seen that a range of pellet sizes existed. A relationship between pellet size and O.U.R. was observed indicating that in a population of pellets ranging from 1mm - 3mm in diameter only those with a diameter less than 1mm were assimilating oxygen efficiently. Using the physiological data collected for A. nidulans growth and metabolism and the relationship between secondary metabolism and morphology, a screen was set up in order to examine the factors which induce secondary metabolism in a range of filamentous fungi with the aim of creating a screen protocol. The importance of morphology and nutrient limitation were examined and it was discovered that in most cases a down regulation of growth rate induced secondary metabolism.