Nitrifying-genes dynamics in the enriched bacterial consortium inoculated with humic soil

In this study, the effects of ammonium concentration (117.5-1155.0 mg-N·1^-1), nitrite concentration (0-50.0 mg-N·1^-1), and temperature (15-35°C) on nitrification performance and its functional genes (amoA-arc, amoA-bac, hao) in an enriched consortium inoculated with humic acid were determined. Notably, the maximum nitrification rate value was observed at 315 mg-N·1^-1 of ammonium, but the highest functional gene copy numbers were obtained at 630 mg-N·1^-1 of ammonium. No inhibition of the nitrification rate and functional gene copy numbers was observed via the added nitrites. The optimum temperature for maximum nitrification performance was observed to be 30°C. The amoA-bac copy numbers were also greater than those of amoA-arc under all test conditions. Notably, amoA-arc copy numbers and nitrification efficiency showed a positive relationship in network analysis. These results indicate that ammonium-oxidizing archaea and bacteria play important roles in the nitrification process.