[Insight into the Process of Mn-ANAMMOX in Soils of Agricultural Drainage Ditches]

Anaerobic ammonium oxidation mediated by MnO₂ (termed Mn-ANAMMOX) is a newly discovered microbial nitrogen removal pathway. However, few studies have reported on the Mn-ANAMMOX process and related microbial communities in agricultural drainage ditches. In this study, Mn(Ⅳ)-reducing bacteria (MnBR) enrichment cultivation was carried out for 340 days and an isotope tracing technique and high-throughput sequencing technology were used to provide convincing evidence of the occurrence of Mn-ANAMMOX. The results showed that simultaneous NH₄⁺ oxidation and MnO₂ reduction occurred during the reaction, and the production of NO₂^-, NO₃^-, ³⁰N₂, and Mn²⁺ was detected. Additionally, the average Mn-ANAMMOX rate, ammonium removal rate, and total nitrogen removal rate were 2.88 mg·(kg·d)^-1, 20%, and 15%, respectively. Moreover, high-throughput sequencing results showed that after 340 d in the enrichment cultivation experiments, the abundance of MnBR increased from 27% to 70% at the phylum level, and the major genera of MnBR were determined as Acinetobacter and Geothrix, with relative abundances of 26.63% and 4.07%, respectively. Overall, the occurrence of Mn-ANAMMOX was directly proven during the MnBR enrichment cultivation experiments, and it might play an essential role in the pathway of microbial nitrogen removal.