[Diversity and PICRUSt2-based Predicted Functional Analysis of Bacterial Communities During the Start-up of ANAMMOX].

Bacterial communities are vital for efficient nitrogen removal in an anaerobic ammonium oxidation (ANAMMOX) system. However, the diversity and functional characteristics of a bacterial community during the start-up of ANAMMOX has not been reported. In this study, an up-flow anaerobic sludge bed reactor was used to start-up the ANAMMOX system, and 16S rRNA high-throughput gene sequencing, combined with PICRUSt2-based functional prediction analysis, was used to investigate the dynamic changes in diversity and function of the bacterial community at different times (d0, d30, d60, and d90) during the start-up. The results showed that 48 phyla, 111 classes, 269 orders, 457 families, 840 genera, and 1497 species were present during the start-up of ANAMMOX. Candidatus Brocadia and Candidatus_Kuenenia were the main detected ANAMMOX bacteria, and their relative abundance was significantly different at different times during the start-up of ANAMMOX (P<0.05). During the start-up, the alpha diversity indices of the bacterial community were significantly decreased (P<0.05), and the structure of the bacterial community exhibited significant spatial differentiation (R=0.846, P<0.01). Functional prediction analysis with PICRUSt2 revealed that the bacterial community was active in organic systems and metabolism at hierarchy level 1, implying abundant functional diversity. Further, the abundance of functional genes was significantly different at hierarchy level 2, during the start-up of ANAMMOX. Forty-nine functional genes involving metabolic nitrogen were detected. The abundance of functional genes, involved in nitrification, denitrification, ANAMMOX, and nitrate and nitrite assimilatory/dissimilatory reduction, changed significantly during the start-up of ANAMMOX.

[Microbial Community Structure and Diversity During the Enrichment of Anaerobic Ammonium Oxidation Bacteria].

To understand the changes in microbial community characteristics during the enrichment of anaerobic ammonium oxidation (ANAMMOX) bacteria, an ASBR reactor was used to culture the ANAMMOX bacteria. The composition, diversity, and species co-occurrence network of the microbial community were investigated under different cultivation times. The results showed that the ANAMMOX bacteria were enriched by gradually increasing the substrate concentration, with removal efficiencies for NH4+-N, NO2--N, and total nitrogen of 97.6%, 95.4%, and 84.9%, respectively. The high-throughput sequencing found that the dominant phyla (relative abundance>5%) were Proteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, Armatimonadetes, and Actinobacteria in the whole culture process. Candidatus Brocadia was the main ANAMMOX bacteria in the reactor, with its relative abundance increasing from 1.42% to 24.66%. During the cultivation process, the composition of the dominant microbial community did not change, while the relative abundance showed a significant difference (P<0.05). The alpha diversity of the microbial community significantly increased first and then decreased (P<0.05), and the beta diversity of the microbial community was significantly spatially differentiated (R=0.5672, P<0.01) during the culture process. Species network densities were 0.188, 0.068, 0.059, 0.18, and 0.0735 at different times during the culture process. Although the enrichment culture process resulted in weaker correlations between microorganisms, the related group of microorganisms in the phylum Aspergillus became the main node in the network. The enrichment process weakened the correlation between microorganisms; however, the microbial taxa related to the phylum Planctomycetes became the key node in the network.