THE USE OF AMMONIUM SOURCE OF NITROGEN IN THE METABOLISM OF ASPERGILLUS NIDULANS EIDAM

Abstract

Aspergillus nidulans was grown as surface cultures on three ammonium salts, namely: ammonium chloride, ammonium carbonate, and ammonium nitrate in a basal medium favorable for fat formation. It was also grown on sodium nitrate for comparison. Growth, uptake of sugar and nitrogen, fat and protein syntheses, and pH change in the culture media were all followed over an incubation period of 20 days at 25° C.Growth on ammonium chloride was suppressed after a short period, when the pH of the medium dropped to a very low value. Mycelial felts had high protein contents but insignificant amounts of fat. In ammonium carbonate cultures, fungal growth continued yielding heavy mycelial felts with high fat content. But nitrogen utilization ceased while an ample supply was still present in the culture medium leading to low protein content in the mycelial felts. This could not be attributed to any drastic change in the pH of the culture medium; the pH changed only within reasonable limits.Growth was best on ammonium nitrate. Mycelial felts contained high protein and high fat. The change in pH of the medium, during the early period of incubation, indicated preferential absorption of ammonium to nitrate ions. Growth on sodium nitrate started by a lag period, but soon became active and gave rise to a heavy mycelium.The present findings also showed that nitrate nitrogen was more conducive to protein synthesis by Aspergillus nidulans than was ammonium nitrogen. Fat formation, on the other hand, was lower on sodium nitrate than on ammonium carbonate or ammonium nitrate.