Efficient nitrogen removal via simultaneous ammonium assimilation and heterotrophic denitrification of Paracoccus...

Although diverse microorganisms can remove ammonium and nitrate simultaneously, their metabolic mechanisms are not well understood. Paracoccus denitrificans R-1 showed the maximal NH₄ ⁺ 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 NH₄ ⁺ was consumed through assimilation. The maximal NO₃ ^- 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 NO₃ ^- was reduced to N₂ for strain R-1 through ¹⁵NO₃ ^- 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 NH₄ ⁺ and NO₃ ^- in a single reactor.