Anaerobic ammonium oxidation coupled with sulfate reduction links nitrogen with sulfur cycle

[Display omitted] •Sulfammox process achieves the simultaneous removal of NH4+ and SO42-.•Candidatus Brocadia sapporoensis &Candidatus Brocadia fulgida dominate Sulfammox.•NH4+ and SO42- were converted into N2, S2- and S0.•Candidatus Kuenenia stuttgartiensis dominates sulfide-dependent denitrification.•Sulfammox is a critical process linking nitrogen and sulfur cycles. Sulfate-dependent ammonium oxidation (Sulfammox) is a critical process linking nitrogen and sulfur cycles. However, the metabolic pathway of microbes driven Sulfammox is still in suspense. The study demonstrated that ammonium was not consumed with sulfate as the sole electron acceptor during long-term enrichment, probably due to inhibition from sulfide accumulation, while ammonium was removed at ∼ 10 mg N/L/d with sulfate and nitrate as electron acceptors. Ammonium and sulfate were converted into nitrogen gas, sulfide, and elemental sulfur. Sulfammox was mainly performed by Candidatus Brocadia sapporoensis and Candidatus Brocadia fulgida, both of which encoded ammonium oxidation pathway and dissimilatory sulfate reduction pathway. Not sulfide-driven autotrophic denitrifiers but Candidatus Kuenenia stuttgartiensis converted nitrate to nitrite with sulfide. The results of this study reveal the specialized metabolism of Sulfammox bacteria (Candidatus Brocadia sapporoensis and Candidatus Brocadia fulgida) and provide insight into microbial relationships during the nitrogen and sulfur cycles.