Changes in development and ultrastructure of Aspergillus niger mycelium in the presence of toxic substances from molasses in citric acid fermentation medium.

Effects of a surface-active agent (Spumol BJ) and toxic molasses compounds on development and ultrastructure of Aspergillus niger strain R-16 mycelium producing citric acid in surface fermentation on molasses medium with 80% yield are presented. Microscopic observations showed that Spumol BJ in concentration of 5 microliters/100 cm3 as well as toxic molasses compounds stimulated the process of swelling and germinating of conidia. Giant conidia unable to germinate, appeared along with typical ones. Delicate mycelium outgrowing from germinating conidia however, sank after 20-24 h culture. Observations of hyphae in electron microscope showed changes in the ultrastructure and dimensions of mitochondria followed by successive degeneration of protoplast. The data obtained indicate that one of the reasons disqualifying raw molasses for biotechnological processes might be the excessive amount of surface-active antifoaming additives.