Metagenomics insights into the selective inhibition of NOB and comammox by phenacetin: Transcriptional activity, nitrogen metabolism and mechanistic understanding

Phenacetin (PNCT), a common antipyretic and analgesic drug, is often used to treat fever and headache. However, the effect of PNCT on nitrifiers in wastewater treatment processes remains unclear. The practicability of attaining partial nitrification (PN) through inhibitor-PNCT was investigated in this study. The optimal treatment conditions of soaking once for 18 h with 2.50 × 10−3 g PNCT/(g MLSS) were applied to the PN stability experiment. The results showed that ammonia oxidation activity recovered quickly after 3 cycles of operation, while nitrite oxidation activity was suppressed steadily. In addition, average ammonium removal efficiency and nitrite accumulation ratio during 138 cycles could reach 94.94% and 85.38%, respectively. Complimentary DNA high-throughput sequencing and oligotyping analysis showed that the activity of Nitrosomonas would gradually surpass Nitrospira after PNCT treatment only once. The decrease of Nitrospira activity was accompanied by the simplification of oligotypes after PNCT treatment, while Nitrosomonas could adapt to PNCT stress by reducing the differences between oligotypes. Metagenomics revealed that the decrease in the number of NXR in the nitrogen metabolism pathways was the key reason for achieving PN. The potential mechanisms might be that the dominant nitrite-oxidizing bacteria and complete ammonia oxidizers were bio-killed by PNCT. [Display omitted] •AOB could recover in the third cycle quickly after phenacetin (PNCT) treatment.•Average NAR of 85.38% was maintained 138 cycles after PNCT treatment only once.•cDNA sequencing and oligotyping showed the activity of Nitrospira was inhibited.•Metagenomics revealed that the reduction of NXR was the key reason of PN.•PNCT prompted a decline in the number of dominant NOB and comammox species.