Lipid accumulation and utilization during microcycle growth of Aspergillus niger.

Aspergillus niger was grown in fermenter culture under conditions promoting microcycle growth. Following a period of spherical growth at elevated temperatures for 24h, conidiophores developed from the swollen giant cells when the temperature was decreased. Each stage in this microcycle conidiation was photographed and dry weight was determined. Aberrant growth forms sometimes occurred and these are described with the measures taken to attempt to minimize such problems. The lipid content and composition was investigated throughout the microcycle by the use of column and thin layer chromatography and by gas-liquid chromatography. The major classes of neutral lipid were triacyl glycerols, fatty acids, sterols and sterol esters. Changes in composition during the microcycle are discussed in relation to metabolic requirements for the different developmental stages and a function for triacyl glycerol as an energy reserve for conidiation is suggested. The fatty acid composition was also determined throughout the cycle and changes related to growth temperature. The accumulation and utilization of triacyl glycerol was indicative of changes in activity of lipolytic enzymes. However little lipase activity was detected, although enzymes which hydrolysed water-soluble esters were more readily assayed. In order to assess the relative utilization of each of the carbon substrates glucose, L-glutamate and L-alanine, they were provided in a radiolabelled form and the fate of the label followed at intervals throughout the cycle. The majority of the material was used in the production of insoluble cellular material, with smaller amounts incorporated into lipids, water-soluble materials or released as carbon dioxide. Very little label from L-glutamate was detected as lipid. Glutamate was principally used during the later, conidiation, stage of the microcycle. The results are discussed in relation to the different physiological stages of microcycle conidiation and to the observed changes in lipid content and composition.