On the metabolism of Aspergillus terreus on ammonium nitrate at different pH values

Abstract

One-week-old fungal mats of Aspergillus terreus Thom were fed with buffered Dox's liquid medium containing ammonium nitrate as nitrogen source and adjusted to six different pH values, namely, 3.0, 3.8, 5.4, 6.8, 8.4, and 10.0. Ammonium nitrogen and nitrate nitrogen absorption and utilization, sugar absorption, respiration, and growth were followed over a period of 72 h at 24-h intervals.Ammonium and nitrate were absorbed at all pH values tested, nitrate being preferentially absorbed at the lower, but ammonium at the higher pH values. Low absorption and utilization of nitrogen occurred at the lowest and highest pH values. Optimum pH for sugar absorption was that for nitrogen absorption, though the former was more sensitive to change of pH than the latter. Rate of respiration was affected by sugar and nitrogen absorption. It was optimum at the same optimum for these two processes.There was release of nitrogen from the mycelial cells to the external medium at all pH values tested, but highest release occurred under different pH conditions and was independent of whether ammonium or nitrate absorption was prevailing.In the fungal mats, more soluble nitrogen and less protein were found at the lowest and highest pH values, while less soluble nitrogen and more protein were found at the optimum pH range; a difference apparently more related to pH than to whether ammonium or nitrate was being absorbed.