Responses of microbial structures, functions, metabolic pathways and community interactions to different C/N ratios in aerobic nitrification

The responses of microbial structures, functional profiles and metabolic pathways during nitrification to four C/N ratios (0, 5, 10 and 15) were investigated in four parallel SBRs denoted as S-0, S-5, S-10, S-15. Results indicated that microbial diversities were affected by C/N ratios, while the same dominant taxa were observed, mainly including Proteobacteria, Betaproteobacteria, Rhodocyclales, Rhodocyclaceae, Zoogloea. The unique biomarkers were identified in each sludge sample through LEfSe analysis. Functional genera/enzymes responsible for removing organics and nitrogen coexisted in four SBRs at different abundances, except for that ammonia oxidizing bacteria (AOB) Nitrosomonas (0.33%-0.66%) and ammonia monooxygenase (amo) (9.4 x 10(-7)-2.8 x 10(-6)) were only detected in S-0. Moreover, PICRUSt analysis indicated similar overall patterns of metabolic pathways in four sludge samples. The network analysis revealed that total nitrogen removal positively correlated with hcp (Spearman's rho of 0.853), and ammonia oxidizing rate was associated with amo (Spearman's rho of 0.096).