GROWTH AND METABOLISM OF ASPERGILLUS NIDULANS EIDAM ON DIFFERENT NITROGEN SOURCES IN SYNTHETIC MEDIA CONDUCIVE TO FAT FORMATION

Abstract

Aspergillus nidulans has been grown in surface culture on high-sugar media favorable for fat formation and containing, as nitrogen source, sodium nitrate, ammonium chloride, or asparagine. Growth, sugar and nitrogen uptake, and syntheses of carbohydrates, proteins, and fat were all followed over an incubation period of 20 days. In the early stages, growth was influenced by the nature of the nitrogen source, being highest on asparagine and lowest on ammonium chloride, with the same sugar uptake. Later, dry weight increase proceeded at a high rate on asparagine, at a moderate rate on sodium nitrate, and it almost stopped on ammonium chloride, where the pH dropped to a very low value. At this stage, increase in dry weight followed sugar absorption, and was due to accretion of non-nitrogenous compounds.Asparagine media were by far superior to nitrate or ammonium media for fat formation. Protein and carbohydrate contents were higher in nitrate- than in asparagine- or ammonium-fed mycelial felts. All synthetic processes almost stopped in ammonium cultures after the early growth phase. It seems that the attitude of the fungus towards ammonium nitrogen could not be fully manifested due to restricted growth, and therefore it is suggested that no definite conclusions with regard to ammonium utilization by Aspergillus nidulans can be drawn unless the pH of the medium is controlled and growth on ammonium nitrogen made possible.