THE UPTAKE AND ASSIMILATION OF AMMONIA BY NEOCOSMOSPORA VASINFECTA

Publisher Website
Google Scholar
Abstract
Summary: A low‐nitrogen mycelium prepared by suspending freshly grown mycelium in a nitrogen‐free medium for 22 to 24 hours was transferred to buffered media containing NH4Cl as sole nitrogen source for estimation of ammonia absorption. In one experiment a 'sugar‐starved’mycelium, obtained by suspending the fresh mycelium for a similar period in a medium lacking both nitrogen and glucose, was employed.During the absorption of ammonia by low‐nitrogen mycelium, there is an increase in the ammonia content of the cells, and also in the total organic nitrogen, showing that assimilation of ammonia takes place. The rate of increase of both forms of nitrogen is greatest during the first 10 minutes of uptake and the maximum level of ammonia in the cells is reached within this initial period. External glucose is required for maximal uptake only after the second hour and it increases only the rate of assimilation. In the sugar‐starved mycelium, uptake of ammonia is considerably smaller: ammonia increases within the cells but ammonia assimilation is very slow in the absence of external glucose.The chief soluble product of ammonia assimilation is glutamine. Ethanol‐insoluble nitrogen compounds are also formed, suggesting that proteins may be synthesized.Assimilation of ammonia is only slightly affected by external ammonia concentration above 5 mM, but is markedly sensitive to temperature, external pH, anaerobic conditions and low concentrations of sodium azide or 2,4–dinitrophenol. The effects of the last three factors indicate that ammonia assimilation depends upon aerobic respiration, including the transfer of high‐energy phosphate. The level of ammonia in the mycelium depends on the external concentration and pH; it is reduced by anaerobic conditions and by sodium azide and 2,4–dinitrophenol although sensitivity to these factors is apparently much smaller than is that of ammonia assimilation. The participation of respiration is therefore implicated both in the assimilation of ammonia and also in some process leading to the increase of ammonia in the mycelium.