Lipid metabolism in Aspergillus niger under conditions of heat shock

The processes of lipid synthesis and decomposition in Aspergillus niger under conditions of heat shock (HS) were studied in a pulse-chase experiment with C-14-labeled sodium acetate. HS (60 min) resulted in the synthesis of phospholipids and sphingolipids intensified compared to the control, as was evident from incorporation of the labeled substrate. The same pattern was observed for neutral lipids, especially for triacylglycerides, while incorporation of the label into sterols remained almost the same. Further cultivation for 3 h in the medium without the labeled substrate resulted in a significant decrease of the label content in the membrane lipids of both the control and the experiment, although under HS conditions this decrease was much more pronounced, especially for phosphatidylcholines and phosphatidylethanolamines. A threefold increase of the label content in phosphatidic acids was observed only under HS conditions. These results indicate more intense metabolism of the membrane lipids under heat shock and suggest the degradation of the major cell phospholipids as the factor responsible for the increased level of phosphatidic acids in A. niger mycelium.