Abstract
Although diverse microorganisms can remove ammonium and nitrate simultaneously, their metabolic mechanisms are not well understood. Paracoccus denitrificans R-1 showed the maximal NH(4) (+) removal rate 9.94 mg L(-1)·h(-1) and 2.91 mg L(-1)·h(-1) under aerobic and anaerobic conditions, respectively. Analysis of the nitrogen balance calculation and isotope tracing experiment indicated that NH(4) (+) was consumed through assimilation. The maximal NO(3) (-) removal rate of strain R-1 was 18.05 and 19.76 mg L(-1)·h(-1) under aerobic and anaerobic conditions, respectively. The stoichiometric consumption ratio of acetate to nitrate was 0.902 and NO(3) (-) was reduced to N(2) for strain R-1 through (15)NO(3) (-) isotopic tracing experiment, which indicated a respiratory process coupled with the oxidation of electron donors. Genomic analysis showed that strain R-1 contained genes for ammonium assimilation and denitrification, which effectively promoted each other. These findings provide insights into microbial nitrogen transformation and facilitate the simultaneous removal of NH(4) (+) and NO(3) (-) in a single reactor.