e., after

408 h), NH4 +, N2O, and NO2 – formed 83.0, 15.5, and 1.5%, respectively, of all N produced and released into the liquid media. These results substantiate the capability of An-4 to dissimilatorily reduce NO3 – to NH4 + (as main product), NO2 – and N2O (as side products) under anoxic conditions. Table 1 Turnover rates of inorganic nitrogen species by A. terreus isolate An-4 during anaerobic incubation with 15 NO 3 – enrichment (Experiment 2) Nitrogen species                           Day 0-3                           Day 3-17 NO3 Src inhibitor – total −166.5 (33.9) −76.4 (13.3) NO2 – total +3.4 (0.4) +1.5 (0.3) NH4 + total +565.4 (74.8) +6.1 (12.4) N2Ototal +5.0 (0.7) +12.5 (0.9) 15NH4 + +175.4 (33.7) +11.1 Tanespimycin mouse (6.5) 15N-N2 +0.7 (0.8) −0.4 (0.2) Rates were calculated for linear increases or decreases in the amount of the different nitrogen species during the early and late phase of anaerobic incubation. Mean rates (standard error) are given as nmol N g-1 protein h-1. Positive and negative values indicate production and consumption,

respectively. Intracellular nitrate storage The capability of An-4 to store nitrate intracellularly, a common trait of large-celled microorganisms that respire nitrate, was investigated during both aerobic and anaerobic cultivation (Exp. 3). Intracellular NO3 – concentrations (ICNO3) were high when extracellular NO3 – concentrations (ECNO3) were high and vice versa, irrespective of O2 availability (Figure  3A + B). Under oxic learn more conditions, however, ICNO3 and ECNO3 concentrations dropped sharply within the first day of incubation (Figure  3A), whereas

under anoxic conditions, steady decreases in ICNO3 and ECNO3 concentrations were noted during 11 days of incubation (Figure  3B). In the 15N-labeling experiment (Exp. 2), the total amount of N produced in each incubation vial (185.4 ± 29.3 nmol) exceeded the total amount of NO3 – consumed (114.4 ± 27.3 nmol), implying that also 71.0 nmol ICNO3 was consumed during the anoxic incubation. The initial amount of ICNO3 transferred into the incubation vials together with the An-4 mycelia of 77.5 ± 28.9 nmol equaled the calculated amount of ICNO3 needed to close the N budget. Production of biomass and cellular energy The production of biomass SPTLC1 and cellular energy by An-4 was studied during aerobic and anaerobic cultivation in the presence or absence of NO3 – (Experiment 4); biomass production was also recorded in Experiment 1. For this purpose, the time courses of protein and ATP contents of An-4 mycelia and of NO3 – and NH4 + concentrations in the liquid media were followed. Biomass production by An-4 was significantly higher when O2 and/or NO3 – were available in the liquid media (Table  2). The biomass-specific ATP contents of An-4 reached higher values when NO3 – was available in the liquid media and were invariably low in its absence (Figure  4B).