terreus isolate An-4 (Experiment 2). The isolate was pre-cultivated

under oxic conditions with 15NO3 – as the only source of NO3 – and then exposed to anoxic conditions. Absolute amounts of (A) 15N-labeled NO3 -, (B) total NO2 -, total NH4 +, and total N2O, and (C) 15N-labeled NH4 + and N2 in the incubation vials are shown. Means ± standard deviation (n = 3). Figure 3 Time course of intracellular nitrate contents (ICNO 3 ) and extracellular nitrate concentrations (ECNO 3 ) (Experiment 3). A. terreus isolate An-4 was cultivated under (A) oxic and (B) anoxic conditions. ICNO3 contents are expressed per g protein of the fungal biomass. Means ± standard deviation (n = 3). The fate of was investigated in Experiments 1 and 2 and additionally in an experiment that addressed the production of biomass and cellular energy during aerobic MG-132 cell line and anaerobic cultivation (Experiment 4). Ammonium was either net consumed or net produced, which depended on the availability of both O2 and (Figures  1A + B, 2B

+ C, and 4A (Exp. 4)). In the absence of was invariably consumed, irrespective of O2 availability selleck chemical (Figure  4A). In the presence of , was either consumed or produced under oxic and anoxic conditions, respectively (Figures  1A + B, 2B + C, and 4A). Taken together, these results suggest a role of in nitrogen assimilation under oxic conditions when is depleted, and a role of NO3 – in dissimilation under anoxic conditions when is available. Additionally, the net production of NH4 + under anoxic conditions suggests dissimilatory reduction to by An-4. Figure 4 Time course of extracellular ammonium concentrations and adenosine triphosphate (ATP) contents of A. terreus isolate An-4 (Experiment 4). (A) Ammonium concentrations in the liquid media and (B) biomass-specific ATP contents of A. terreus

isolate An-4 were determined during aerobic and anaerobic cultivation in the presence or absence of NO3 -. ATP contents are expressed per g of protein of the fungal biomass. Means ± standard deviation (n = 3). Products of anaerobic nitrate turnover The precursors, intermediates, and end products of dissimilatory Dichloromethane dehalogenase NO3 – reduction (i.e., NO3 -, NO2 -, NH4 +, N2O, and N2) by An-4 were investigated in a 15N-labeling experiment (Exp. 2). Axenic mycelia were incubated with 15NO3 – and then subjected to a sudden oxic-anoxic shift. The anaerobic consumption of NO3 – by An-4 was accompanied by the production and cellular release of NH4 +, NO2 -, and N2O, but not N2 (Figure  2A-C). Ammonium was quantitatively by far the most important product, whereas N2O and NO2 – were less important (Figure  2B + C, Table  1, Additional file 1: Figure S1). Biomass-specific 15NH4 + production rates equaled 15NO3 – consumption rates during the first 3 days of incubation (Table  1). During the remaining incubation time, N consumption and production rates were generally lower than during the first 3 days (Table  1).