High dosage of exogenous glycine in cross-feeding breaks the equilibrium of anammox system.

• TNRE increased to 87.89 ± 1.82 % after dosing low concentration exogenous glycine. • Candidatus Brocadia and Candidatus Kuenenia emerged as primary enriched genus. • Glycine modulated nitrogen metabolism by altering the content of Hzs & NirS genes. • High dose of exogenous gly in cross-feeding broke the equilibrium of anammox system. • Gly cleavage system could be the initiating point for the cross-feeding imbalance. Strategies to break the cross-feeding equilibrium by dosing essential metabolites and thus enriching and isolating anammox bacteria (AnAOB) have been proposed, but amino acids have not been investigated as important cross-feeding pathways in anammox consortia. In this study, long-term experiments were designed to verify the effect of exgenous glycine on anammox consortia and changes in the bacterial community and metabolic activity after the addition of glycine in a highly active anammox system were investigated. The results showed that the impact of glycine on the activity of anammox highly depended on glycine concentrations, which was manifested as a promotive effect at low concentrations (0–150 mg/L) and an inhibitory effect at high concentrations (300–600 mg/L). The addition of low concentrations of glycine not only enhanced the diversity and richness of bacterial communities but also promoted the enrichment of Candidatus Kuenenia. The qPCR results showed that the content of functional genes Hzs, NirS and anammox 16S rRNA increased while the expression of amoA and NrfA genes was suppressed when glycine acted positively on AnAOB; Hzs and amoA were suppressed when glycine acted negatively on AnAOB, while the expression of NirS and NrfA genes increased dramatically. Specific anammox activity (SAA) experimental results show that 50–150 mg/L glycine was the optimal amount for promoting the activity of AnAOB. Analysis of community metabolic functions indicated that the addition of exogenous glycine resulted in a imbalance of glycine cross-feeding and promoted AnAOB enrichment mainly by affecting pathways such as other glycan degradation and Lysosome. Overall, this study provided new insights into understanding the glycine cross-feeding, which is essential for improving anammox-based technologies. [ABSTRACT FROM AUTHOR]